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BSAVA Manual of Small Animal Fracture Repair and Management Edited by

Andrew R. Coughlan BVSc PhD CertV A CertS AO FRCVS Animal Medical Centre 5 11 Wilbraham Road, Cha rlton Manchester M2 1 I UF, UK a nd

Andrew Miller BVMS DSAO MRCVS Willows Veterinary Centre, 78 Tanworth La ne Shirl ey, Solih ull B90 4DF, UK

Publ ished by:

Britis h Small An imal Veterina ry Association Kingsley House, Church Lane

ShurdinglOll, ChcllcnllHlll GL51 5TQ, United Kin gdom A Company Limited by Guarantee in England. Registered Comp;my No. 2837793. Registered as ,I eh"Tity. Copyright © 1998 BSAVA All rights reserved. No p.1rl Of lhis publication Inay be reproduced, stored in a retrieval system, or tr;msmittcd, in fonn or by any means, electronic, mechanic,ll , photocopying, recording or otherwise without prior wriucn permission of the copyright holder. All the colour illustrations in this book have been designed and created by Vicki Martin [X--sign, Cambridge, UK and arc printed with their pcnn ission. A cata logue record for this book is available from the Britis h Library

ISBN 0 9052 14374 The publishers ~nd cOlllributors cannot take responsibility for information provided on dosages and mcthods of applic3lion of dru gs mcntioned in this publication. Details o f this kind must be verifiL'd by individual uscrs from the appropriate litera ture. Typeset and printed by: Fusio n Design, Fordingbridge, Hampshire, UK _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __

C.OLl h

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iii

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Contents Contents

iii

List of Contributors

Foo'eword

Preface

vii

PART 1

Background to Fracture Management Fmcture Classification and Description

D. Gary Clayton Jones 2

History of Fracture T"eatment Leslie C. Vaughan Biomechanical Basis of Bone Fracture and Fracture Repair

Simon Roe

Fracture Healing

Tim M. Skerry

Imaging of Fracture Healing

D. Gary Clayton Jones

PART 2

Principles of Fracture Management

Evaluating the Fracture Patient

Ralph H. Abercromby 7

Non-surgical Management of Fractures

Jonathan Dyce

Instruments and Implants

John P. Lapish

Principles of Fracture Surgery

Andrew Miller 10

Complex, Open and Pathological Fractures

Chris May II

Fractures in Skeletally Immature Animals

103

Stuart Carmichael

PART 3

Management of Specific Fractures

The Skull and Mandible

115

Harry W. Scott 13

133

The Spine W. Malcolm McKee

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The Scapula Andy TorringTOn

161

The Humerus Hamish R. Denny

171

Radius and Ulna Warrick 1. Bruce

197

The Pelvis and Sacroiliac Joint Marvin L. Olmstead

217

The Femur A. Colin Stead

229

Tibia and Fibula Steven J. Butterworth

249

Carpus and Tarsus John E.F. HOltltoll

265

The Distal Limb Jonathan Dyee

283

Patella and Fabellae Ralph H. Abereromby

293

PART 4

Complications of Fracture Management

Fracture Disease John F. Ferguson

305

Implant Failure Malcolm C. Ness

311

Osteomyelitis Angus A. Anderson

317

Complications of Fracture Healing David Benneu

329 341

Index

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PART ONE - - - - - - - - - - - - - - -

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Background to Fracture Management

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CHAPTER ONE

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Fracture Classification and Description D. Gary Clayton Jones

INTRODUCTION A method for classifying fractures is needed to be able to describe fractures for a variety of reasons. An accurate descri ption of a fracture enables surgeons to discuss methods of diagnosis, treatment and prognosis and to compare results, thus providing easier verbal and written communi cation. The use of a

si milar fracture classification system for small animals and for humans could provide a basis for comparati ve studi es between spec ies. An accurate classification could assist in pl anning for patient requirements or ordering implants in quantity, which may be essential in a large hospital. Many of the terms in current usage are man y

centuries old and relate to outmoded or superceded practices and problems. Initially fractures had to be described verbally, as the only alternati ve would have been to draw diagrams. The difficulty with verbal descriptions is that there is no internationall y agreed definition for the terms that are commonly employed. For example, how angulated maya fracture plane be fo r the fracture still to be described as ' transverse'? The problem increases with the lack of a common lang uage, as similar terms may ha ve dif-

becomes for the user to classify each fracture in the same way as other workers and therefore the greater is the opportunity fo r va riation and subsequentl y reduction in value of the data. For this reason no single system of fracture classification or description has yet been adopted internationally for sma ll animals. A system of fracture classification (Muller, 1990; AO/ASIF, 1996) has been developed for use in human patients by the AO/ASIF (Arbeitsgemeinschaft fur Osteosynthesefragen/Association for the Study oflnternal Fixation) Group using alphanumeric classifications combined with electronically stored X-ray images. The central store can be remotely accessed but requires considerable computer power at the recording centre, although a PC, scanner and modem are the only requirements at the hospital. Both recording of data and the requesting of data and information can be made from a hospital office. A computer-based CD-ROM or diskette system is now available for equine fra ctures (Fackelman, 1993).

METHODS OF DESCRIPTION Earl y methods of describing fractures were based on

ferent meanings and therefore transmi ssion of data

va ri ous anatom.ical features or on using eponymous

between countries is made even more difficult. The value of exchange of data is obvious, as some fracture types are rare and individual ex perience may be very limited, apart from the important needs of educational exchange. Prior to the advent of X-ray exa mination, photo-

fracture descriptions, often named after the first observer (or sufferer) . The most commonly recognized of such names are probably Colles, Potts and Monteggia. These human medical terms are occasionally used in veterinary practice but are of little va lue unless the explanation is already known. Such eponymous descriptions should therefore probably not be used in veterinary practice. The discovery of X-rays in the latter part of the nineteenth century allowed a more acc urate form of description based on the radiological

g raph y, fax trans mission and scanning, th e use of

prepared diagrams would ha ve been very laborious it is becoming more possible to scan fracture images and transmit the information electronically to some central point for pictorial anal ysis and recording by computer, or possibly for rapid advice from a specialist. An alternati ve is to classify fractures into groups identified from a series of definitions that can be identified by various alphanumeric symbols. The problem is to decide at the outset how much information is required from the data and thence the complexity of any coding system. The more complex the system, the more difficult it and ineffici ent. C urrently

appearance of the fracture .

The earliest description of a fracture was whether or not the fracture was 'simple' (closed) or 'compound' (open). This stems from the period prior to antibiotic therapy when an open fracture carried a high risk of infection and potential loss of the limb or often of the patient. Today the words closed and open are more commonly used to refer to the same clinical features .

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Manual of Small Anjmal Fracture Repair and M anagement

The ex pression 'simple' was used to imply ease or difficulty of treatment, but this was related to the aspect of fracture infection. Some simple fractures may be very difficult to reconstruct, while some open fra ctures can be straightforward two-piece fractures that are mechanicall y easy tomend. Closed is now also used to describe a single circumferential disruption of the diaphysis. (Small cortical fragments of less than 10 % of the circumference are ignored as they probably ha ve little significance for treatment or prognosis.) Open (compound) fractures are now generally

Specific Greater trochanter

Tibial tuberosity Lateral condyle, etc.

Displacement of the fragments Greenstick Guvenile) Folded Fissure - undisplaced fragments which may displace at operation or under stress

classi fied into varioLis types which have a more modern clini ca l significance from the point of view of treatment and prognosis. 'Compound ' does not indi-

D epressed -

cate the number or type of fragmentation, though the wo rd is commonly misused to imply a difficult or fragmented fracture. Complex implies the difficulty or severity of the

cavity, es pecially parts of the slmll Compression - of cancellous bone, often vertebral body Impacted - cortical into cancellous bone.

fra gments in vade an underl ying

fra cture, and ca n be defined as desc ribing a

multifragmented fracture of the diaphysis in which there is no contact between the proximal and distal segments aft er reduction. Pathological (or secondary) fractures are a par-

Nature of the fracture line

which the fractures result from failure of bone strength

Complete - all of the cortices are broken with the separation of the fragm ents Incomplete - part of the bone remains

from an underl ying cause such as bone tumour, infec-

intact.

ticular form, not related to trauma in every case, in

lion or osteodystrophy . The initiating defect may not always be readil y identified by X-ray. Compl icated fractures are those in which there

Complete fractures ma y a lso be desc ribe d in

is major blood vessel, nerve or joint in vo lve ment. Th e description is not so commonly used in veteri -

terms of:

nary orthopaedics. These are often more serious in human patients, where loss of major arterial suppl y

Di,.ectioll offractu,.e !ille

may cause perman ent loss of functi on of a vital organ e.g. th e hand, or even result in an amputati on.

Closed (simple) fractures There are various criteria that can be used to define different types of closed fracture: Anatomical location The bone shaft (diaphysis) has been conventionall y divided into thirds: proximal (upper), middleanddistal (lower).

Transverse -

the angle of the fracture line to

a perpendicular to the long axis of the bone is less than 30" Oblique - the angle is equal or greater than 30". Spiral - the result of torsion Longitudinal, Y or T fracture, saucer.

Numbe,. 0,. type of fragments Two-fragment, three-fragment, comminuted (many fragments, i.e. more than two);

Anatomical feature

sometimes multi fragment is pre ferred. Wedge fragments - the main fragments have

General

some contact after reduction Segmental - large one or more complete or

Capital Subcapital Metaphyseal Diaphyseal (shaft) Sub trochanteric Physeal Condylar Articular.

almost complete fragments of shaft Butterfly (intermediate) fragment Irregular - a diaphysea l fracture with a number of intermediate fragments with no

specific pattern, usuall y accompanied by severe soft tissue lesions

Multiple - more than one fracture in same or different bones.

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Fracture Classificati on and Description

Stability following retiuction

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This has been termed the Charnley classification and was used to determine which fractures wo uld respond to closed reduction and fixation. Stable after reduction - tends to remain in place without force Unstable after reduction - fracture collapses as soon as reducing force is removed.

AccessOlY carpal bOlle (JOhIlSOIl, 1987) Type I - intra-articular avulsion of the distal margin Type II - intra-articular fracture of the proximal margin Type III - extra-articular avulsion of the distal margin Type IV - extra-articular avulsion of the insertion of fl exor carpi ulnaris at proximal palmar surface

Nature offractllre origin

Type V - comm inuted fracture of the body which may in vo lve the articular surface.

Avulsion/apophyseal - pulled by tendon or ligament Chip - small fragm ents at articular margin followin g hyperextension injury Slab - larger fragment with a vertical or very oblique fracture of a small cancellous bone which may extend into both articular surfaces.

Articular fractures

Extra-articular - not involving the joint surface but may be intracapsular Partial articular - involving only a part of the articular surface, with the remaining articular cartilage surface being attached to

the diaphysis Complete articular - disrupting the articular surface and separating it completely from the diaphysis (e.g. Y or T fracture) .

Special classifications Growth plate or epiphyseal fractures (separations) The most commonl y used is the Salter-Harris system (Salter and Harris, 1963) in which six types of injury are recogni zed (see Chapter II): Type I - complete, through the hypertrophied cartilage cell zone Type II - partially includes the metaphysis Type III - intra-articular fracture to the hypertrophied zone and then along the epiphyseal plate to the edge Type IV - intra-articular fracture that traverses the epiphysis, epiphysea l plate and metaphysis Type V - crushing injury that ca uses destruction of growing cells

Type VI - new bone bridges the growth plate. Classifications of special joint fractures Certain specific fractures (mainly because of their importance in the racing Greyhound) have been classified to aid prognosis and treatment.

Central tarsal bone (Dee et aI., 1976) Type I - small dorsal slab fracture with minimal displacement Type II - dorsa l slab fracture with displacement Type III - one-third to half of the bone fractured in the median plane and displaced mediall y or dorsa ll y Type IV - combination of Types II and III Type V -

severe comminution.

Various combinations of fractures of the tarsus (see

Chapter 20) are regularl y seen concurrently in the Greyhound, but are not classified, although they have been described as triads (Newton and Nunamaker, 1985).

Metacmpal/metatarsalfract"res (Newtoll allti NllIzamakel; 1985) Type I - painful on palpation at the junction of the proximal fourth/third and distal twothirds/three-quarters of the bone; endosteal and cortical thickening of the bone on X-ray Type II - hairline undisplaced fi ssure type fracture

Type III - complete fracture with palmar/ plantar displacement of distal fragment.

Open fractures Open fractures possess a wound which communicates

between the fracture bed and the outside environment. Usually tltis is via a visible surface wound but could describe a fracture of a skull bone which has penetrated the nose or a sinus cavity. Classification of open fractures is often he lpful in detennining optimal meth -

ods of treatment. Type I - a fractur!' produced from inside to outside by the penetration of a sharp fracture fragment end through the overlaying soft tissues. Such a fracture may become open

some time following the initiating incident as a result of uncontrolled or unsupported

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Manual of Small Animal Fracture Repair and Management

movement. There is usually limited soft tissue injury and the bone fragments are all present,

There is usuall y more soft tissue damage with contus ion around th e s kin wound and some

lag phase in which the bacteria become established, the organisms may begin to multiply, turning a contaminated wound into an infected one. This is the concept of a 'golden period' which should be taken into account but not relied upon implicitly. A system for classification of the soft tissue injury has been developed for use in humans (Muller el al ., 1992) (Table 1.1). Certain evaluations in human pa-

mainl y reversible muscle damage. Fractures may be more fragmented but there is little if any loss of bone or soft tissue.

system may be too complicated for animals, although it could probably be used with a little variation.

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often with out comminution.

Type 2 - a fracture caused from outside to inside by penetration of a foreign object.

Type 3 - the most severe form of open fracture in which loss of tissue fo llowing

penetration by an outside object has resulted. Loss of skin, soft ti ssue and bone material may have occurred and may be very severe. Some workers recognize a s ubdivision in

which loss of the main arterial suppl y to the limb has occurred, as this indicates mandatory amputation. Although not offi cially recognized, an estimate of the time elapsed since the injury may be helpful in classifying an open fracture. This acknowledges the dangers of bacterial invas ion of a wound where, after an initial

ti ents are not made in veterinary patients and so the

Fracture classification suitable for computer analysis The ability to classify fractures for computer analysis is clearly the best method: it would readily allow anal ys is and comparison of data as well as easily allowing worldwide cooperation. A number of meth-

ods have been attempted but currently no single method has gained acceptance. A method of classification of femur fractures was developed at the Uni versity of Michigan (Braden, 1995) following a general anal ysis of fractures by Brinker (Brinker el al., 1990). This system is on ly applicable to fractures of the femur and has a limited ability for fracture description. It is based on a paper

Illtegumellt Closed (IC) [CI [C2 [C3 [C4 [C5

No injury No laceration but contus ion

Circumscribed degloving Extensive closed degloving Necrosis from contusion

Illtegumellt Open (10) [01 [02 [03 104 [05

Skin breakage from inside out

Skin breakage from outside in > 5 em, contused edges Skin breakage from outside in < 5cm, devitalized edges, circumscribed degloving Full thickness contusion, abrasion, sldn loss

Extensive degloving

Muscle/ Telldoll (MT) MTl MT2 MT3 MT4 MT5

No injury Circumscribed injury, one muscle group only Extensive injury, two or more muscle groups

Avulsion or loss of entire muscle groups, tendon lacerations Compartment syndrome / crush syndrome

Neurovascular (NY) NVI NV2 NV3 NV4 NV5

No injury [solated nerve injury Localized vascular injury Combined neurovascular injury

Subtotal/total amputation

Table 1.1: A system /or classification a/soft fiSSile injuries (designed/or lise in hUl1Ians).

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Fracture Classification and Description fonn which can be an alysed by computer; thus no computer eq uipment is required at the hospital. General classification of fractures was developed by Muller and others of the AO/ ASIF group for human fractures (Muller, 1990; CCF, 1996) . Thi s has been modified by various workers to create similar methods for small animals and the horse. Two systems for small animals, the Prieur (Prieur et aI. , 1990) and the Unger (Ungeretal., 1990), have been described in the literature although neither has yet been accepted universally. These classifications describe the bone, th e location and the type of fracture . Each of the proposed systems creates a four-digit record in a similar way to the human AO system. The Prieur and U nger fracture classification systems can only be used for fractures of the long bones and are not used for fractures in vo lving the s kull, vertebral column, pelvis or small limb bones. Neither system discusses the soft tissue problems, which may well be of the greatest importance in determining

Transve rse ~

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.....

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J J

, ".

.....

({I)

(b)

J J

~ (e)

.. (d)

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Figure 3.3: Thefracture configuration is afunction oftlle/orces acting all tile bone. (a ) Compression: the minerat struclllre shears at 45 0 to the long axis, producing oblique fraclUre lines. (b) Tension: bone is weaker ill tellsion because the mineral crystals contribute little. failure occurs by separation ill a straight tille. (c) Rotation: shear fo rces create a spiral /racture pattern. (d) Bendillg: tension develops on the convex sill/ace alld compression on the concave surftlce as the bone bellds. Because the bOlle is weaker intension. Ihe/raclure begins transversely. As il travels across the bone, the forces change to compression Gild Ihe fracture often progresses ill bOlh 45 0 directions to create a 'butterfly' Jragmem. (e) Combined bending and compression: all increase in the compressive stress resulrs ill shear failure ear/ier and a larger 'butterfly' Jragmem results.

comminution. The highly comminuted femur fracture in Figure 3.4 occurred when the dog leapt from a truck travelling at 35 mph. When the dog's foot contacted the ground and stopped moving forward, his body continued, creatin g a massive torsional load in the limb. This was combined with a massive compressive load from the landing body and the contraction of the tlligh muscles in an attempt to prevent falling. Cancellous Fracture of cancellous structures follo ws some of th e patterns seen for cortical bone. In compression, however, collapse and compaction occur. It is important that this type of change be noted when evaluating a fracture as it will influence the ability to reconstruct th e bone and to appl y an implant to it. Tilis type of fracture is most commonl y seen in vertebrae.

MECHANICAL ASPECTS OF FRACTURE HEALING The various stages of callus maturation are influenced by local humoral and physical fac to rs. The

stress and strain ex peri enced by th e tiss ues wit11in the fracture influence the ir develo pment and d ifferentiation. The ty pes of tiss ue prese nt in vari o us regions of the ca llus are often dictated by their tolerance of the loca l deformation s. Early in the healing process, th e fracture gap fills wi th granulation tiss ue. The loose, fibrous nature of this tissue allows it to tolerate strains in the region of 40%. Because strain is calcul ated fro m the ori ginal length of th e tissue being loaded, one way that nature is able to reduce tissue strain is by increasing the width of the fracture gap. Resorption of fracture ends occurs when large motions are present (Fig ure 3.5). A5 the biological processes drive callus differentiation, regions with less strain become more fibrous and cartilaginous matrix is deposited. This tissue is stiffer less movement of the fracture frag ments will occur with the same load. However, it is also less tolerant of strain. Ifit is distorted by more than5 %, tissue injury will occur, differentiation will be reta~ded, and more granulation tissue will be laid down. If the stiffening of the callus does control movement, mineralization and woven bone formation begin. Again, this corrunences first in regions of the callus with the least motion. The tissue is stiffbutmore

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Manual of Small Animal Fracture Repair and Management

susceptible to injury - more than 0.2 %strain will damage the mineralized matrix. If tissue strain is minimal during the bridging period, the newly fomled bone can provide sufficient strength to join the fracture ends. The final maturation process is also influenced by the mechanical environment of the bone. Loading is sensed by the osteocytes of the inunature callus and remodelling by 'cutter cones' and the development of an Haversian system result in re-establishment o f cortica l structure. In a fracture in which the implant eliminates fracture fragment movement, the earlier phases of tissue differentiation may be bypassed, and primary bone healing by the cutter cones and gap filling will combine to repair the bone.

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Pelvis

Os Penis

MECHANICS OF FIXATION TECHNIQUES

Figure 3.4: Litle drawing oj a radiograph of a highly comminuted Jemurfraclllre that occurred when the dog leapt Jrom the back of a truck moving at 35 mph. When the fool lallded alld stopped and Ihe body comil1ued moving, massive torsionalJorces were applied. These com billed with Ihe compressive forces of body weight and of the thigh muscles. The fraclllre developed II/any cOlllminutions because of the large amoullt oj energy alld the rapid rale of loading. Narrow fracture gap

Large tissue strain

'>.,

(a) _ _....LL--_ _

Wide fracture gap

Smaller tissue strain

~ I-Ll-

i I-rr-

(b)

Figure 3.5: (a) Wh en the fracture gap is small, the tissues withill the gap experience a large amOUII! ojstrain because a smail all/oulll oj 1Il0vemel1f is distributed over a short length of tissue. (b) Wh en theJracw re gap is wider, the strain is reduced as the same amount oj de/ormation is distributed over a longer length.

An understanding of the mechanical characteristics of the implants commonly employed in fracture repair is necessary if a surgeon plans to minimize the strain in tile fracture callus so that healing can occur. TillS section will begin by presenting a method used by the author to assess implants in general and individual fracture repairs. TillS method simplifies the likely forces acting on an implant and provides a basis for evaluating stability of a repair.

Forces acting on an implant During a gait cycle, weight bearing and muscle contraction result in a complex array of forces within a bone or bone-implant construct. Studies of these forces are difficult and have provided limited data, but for improvin g clinical judgement in orthopaedics it is usually sufficient to take a much more simplistic approach. The forces acting on a bone or implant are a combination of ax ial compression, bending and rotation (Figure3.6) . In some specific instances, fragments associated with the origin or insertion of major muscle groups may experience mostly tension. This scenario will be addressed in a separate subsection. Axial compression is the component of the forces aligned down the shaft of the bone. When acting on a fracture, it causes collapse and shortening. Weight bearing and muscle contraction will contribute to this component. When evaluating an implant for its ability to counter this force, the purchase obtained in the major proximal and distal fragments must be considered. The ability of a fracture repair to resist compression will also be influenced by the completeness of reconstruction. Bending is present whenever a bone is bearing load and it is not perpendicular to the ground. Eccentric muscle contractions can also apply bending forces in any direction. An implant's resistance to bending is deternlined by the elastic modulus of the material it is made of and its area moment of inertia (AMI). Implants made from 316L stainless steel can be generally

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Biomechanica l Basis of Bone Fracture and Fracture Repa ir

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Axial compression

Torsion

Bending

It is also necessary to determine the AMI at the wea kest point of the structure that wi ll be loaded. It is easy to calculate the AMI for circular or rectangular structures but, if a hole in a bone plate or interlocking nail is bearing load, then this will be the weakest point. The AMI of the solid portion of a 3.5 mm plate is 29.9 mm' while tllrough a hole it is 14.8 mm' - a 50% reduction. If a screw hole in an interlocki ng nail is located close to a fracture, it should also be considered a weak point in the construct. For the 8 mm nail, the AMI drops from an impressive 201 mm' for the solid section to 64.7 mm' in the weakest di rection. Torsion is induced by changes in the direction of the body while the limb is bearing weig ht. Assessment of rotational stability is often more complex than compression or bending. The polar moment of inertia (PM!) of the implant is not usually a weak point in the construct. Stabi lity is estimated by how well the implant engages the primary fracture fragments. Rotational stability may also be im parted by interaction of the fracture fragments. The way in which different systems are assessed wi ll be discussed in the specific sections below.

External coaptation

Figure 3.6: Diagrammatic representation of the three force categories considered when evaluating a fracture. CljixCltioll method. or a repairedfractllre. Weight bearing alld muscle COl/tractions contribllte to compressive forces down the 10l/g axis. Wh ell the bone is at all angle to the ground or when the muscles pull more 011 one side thall 011 the other, belldillg will be indllced. This lIIay be ill allY direction. Torsion will occllr when the mass of tlte body changes direction while the lim b is bearing weight.

compared based on their AMIs. Titanium has a lower modulus and implants of similar AMI wi ll be less stiff. However, titanium resists fati gue damage under re-

peated loading better than stainless steel. Since most implants fai l by fatigue rather than from a single excessive loading event, this property must also be allowed for when assessing an implant's suitability to maintain fracture stability until healing has occurred. Because calculation of the AMI of a structure is based on the direction of bending, it is necessary to estimate this for a repair. In most bo nes, a primary

direction is not evident and the smallest AMI, which determines the weakest direction, is used to character-

ize the weakest point in bending. In the femur, the eccentric location of loading through the femoral head dictates a lateral to medial bendi ng direction.

Splints and casts provide immobi li zation of fracnIre ends by encasing the limb. They do not directly contact bone and so must act tllrough the skin and muscles of the limb. The cast or splint material is the most rigid portion and it must be built wit h sufficient strength to withstand the forces that will be applied to it for the appropriate duration. Bending forces are the most significant forces because casts span joints and there is a great propensity for the limb to want to bend at the level of the joint. There are a number of ways of improving cast design and construction to counteract

the bending forces. Thickness ofthe wall of the cast is the most obvious approach but the disadvantage is that the cast becomes heavier. If the primary bending direction is known , th e cast ma y be reinforced in that

specific plane. This wi ll increase the AMI (because the added dimension is in the plane of bending) without adding too much weight. It is also beneficial to form a cast that is relatively straight but this tends to lengthen the limb and is more awkward fo r the patient. The interface between the cast and the bone will also influence the ability of the cast to immobilize the fracture fragments. The greater the stiffness of this interface, the better wi ll the rigid cast material support the fracture. High stiffness is produced by using little or no cast padding and by applying the cast wrap with pressure. Both these approaches increase the likelihood of pressure injury to the skin and soft tissues between the cast and the bone. The surgeon must therefore judge the correct amount of padding and cast wrap pressure that wi ll avoid soft tissue injury but will still provide adeq uate immobilization of the fracture fragments.

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External skeletal fixators P in factors The strength of the purchase of the pins in the fract ure fragments is an important factor in the success of external fixation (Figure 3.7). Indi viduall y, smooth pins rely on compression of the bone against the pin shaft to resist pull-out. In most frames, multiple pins are placed and they are purposefull y angled to each other so that they brace each other. Threaded pins are more secure ly anchored in bone. Negative thread profiles were used initially because they are easier to manllfactllre~ however, they are weak at the point where the shaft and threads meet and pin breakage was frequently seen. The Ellis pin was designed with a short negatively threaded portion so that only the fa r cortex was engaged with thread and the thread-shaft junction was protected by being inside the bone. Breakage was seen occasionally following resorption of the bone of the near cortex . Positive profile threaded pins are now available. The threads are created by a lathing or ro ll ing process. The shaft diameter is not significantly reduced and therefore the bending strength of the pin is not compromised. Because the thread diameter is greater, the purchase of the pin is also greater than for negati ve profile pins. This larger diameter does make these pins a little more awkward to place as the tlueaded portion does not fit through the hole in the external fixator clamp. The surgeon must select the appropriate diameter pin for each situation. The larger the diameter, the stronger the pin wi ll be in bending and the stiffer the frame will be, overall. This must be countered by the size of the bone into which the pin must be placed. As a general ru le, the diameter of the pin should not exceed 30 % of the diameter of the bone so as not to weaken the bone. This may be difficult to comply with when placing pins in the mediolatera l plane of the radius or in the metacarpals or metatarsals. The rigidity of a fixator is increased by increasing the number of pins in each fragment. Two is a minimum and four is considered the maximum in most small animal applications. Obviously, pin diameter and frag ment size wi ll dictate what can actuall y be acllieved. Pins shou ld be spaced evenly over each fragment, as this increases torsional ri gidity of a fram e. They should be placed as close to the fracture as is considered safe. This is detennined by the possible presence of fissures and the size of the bone. If there are no fissures, an estimate of this safe dista nce is three times the diameter of the pin being used. Because stiffness of a structure is influenced by its length, the pins closest to the fracture should be angled towards each other so that the span of the connecting bar that bridges the fracture is minimized. A final factor that influences the stiffness of a fixator is the length of the pin. Clamps are oriented so

that the clamping bolt is closest to the skin. Sufficient distance must be left between the clamp and the skin to allow for some swelling. The surgeon can reduce the length of the pin by selecting a location with the least soft tissue. This also reduces the tissue irritation caused by the pin and appears to reduce the incidence of pin track drainage and infection. In the beginning of this section, the advantages of threaded pins in increasing the immediate strength of the pin-bone interface was described. It is of eq ual importance for the surgeon to consider the long-term stability of the pin -bone interface. Loosening o f pins is the most common complication of external fixation. It causes discomfort for the patient and ma y affect the hea li ng process. The mechanica l aspects of pin placement feature heavily in the maintenance of a stable interface. Threaded pins loosen less frequently, because they mechanicall y lock into the bone. The more pins that are present in a fragm ent, the less is the load at each interface and, therefore, the less likely is loosening. The amount of bone injury that occurs during pin place ment is also a major determinant of how the bone around the pin will change during hea ling. Significant thermal injury causes bone necrosis.

(a)

Weak p a i n t ,

c, (b)

\ 1 .1111 11111 , 111 .111" Weak point protected

.1 , 111 .1 11"

(e)

t (d)

.t \'.\ \ \ \ \\\\\' \\ \ \' .\ \\'

Shaft diameter-1 not reduced -

Lar9 er ma'or diameter

Figure 3. 7: Types oj pillS Jar external jixators. (a) Smooth pillS rely ol/frictioll \\lith rhe bone or bracing against other pillS in rheframe. (b) Negative-profile threaded pillS engage the bone more securely bw are sllsceptible to Jailure at the shaft- thread jUllction. (c) Ellis pins have a small length of negative-profile thread, designed to engage only one cortex. The \\leak point a/the pill is protectedfrom bending forces. (d) Positive-profile threaded pillS have a larger major diameter, so holdillg strength is increased. Becallse the sllaft diameter is flot reduced, (h ey are better able to resist tile cyclic bendillg forces associated witll weight bearing.

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Biomechanica l Basis of Bone Fracture and Fracture Repair

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t~ t -,(b)

(e)

Figure 3.8: (a) Axial compression dOlVn lhe shaft 0/ a/raclllred bone supported by a unilateral external fixator results ill bending 0/ llie pins and lhe connecting bar. (b) Axial compression 0/ a bilateraL /rame results ill bending o/the exposed lengths 0/ rlie pills. (c) Bending/orces directed Ollt 0/ the plane 0/ a bilateraLframe result in bending 0/ the cOllnectillg /XII"S. By addillg a third IXII' ill a nother plane, the frame is beller able 10 resislthese forces.

Microcracking reduces the strength of the supporting bone and stimulates a repair respo nse. Resorption

to re move the dead and damaged bone ma y reduce the strength of the interaction between the bone and pin . Movement at the interface wi ll prevent new bone formation and a fibrous interface will develop. Movement will al so injure these tissues, causing pain and stimulat ing an inflammatory res po nse .

Once it starts, the process often becom es self-perpetuatin g. To reduce thermal injury to bone, pin tracks should be pre-drilled with a drill onl y s lightly smaller than the shaft diameter, or pins with efficient cutting tips should be used. Pre-drilling also reduces the amount of microcracking in the s ur-

complex frame should be applied. A bi latera l frame e mploys connecting bars on each side of the bone. Axial compressive forces will now be resisted by the pins (Figure 3.8b): their diamete r, numbe r and exposed length will determine the stiffness . Bending in the plane of the fi xator is also well resisted because the connecting bars protect each other. Bending in the plane perpendicular to the fixator is resisted by the connectin g bars on ly: their exposed length and diameter are determining factors of ri gidity. Torsional forces also are better resisted by bilatera l frames as the connecting bars are distributed around the axis of rotation. Triangular configurations are selected to improve

the bending stiffness of a frame (Figure 3.8c). The

rounding bone.

connecting bar in the second plane imparts resistance

Frame configuration The forces that act on a fracture - axial compression, bending and torsion - must be considered when assessing the suitability of a fi xator fram e configuration. The simplest frame is a unilateral design. Compression will cause bending of the connecting bar (Figure 3.8a). Thediameterofthe bar and the size and number of pins will influence the performance of the frame. The inherent stability of the fracture must also be considered. If the fracture is transverse, it will not be able to collapse and the bone will reduce the load placed on the fi xator. Ifthe fracture fragments do not interact, the frame must bear all of the load through the limb. Bending forces will be resisted similarl y by a unilateral frame. To increase the res istance of a unilateral frame to bending, a second connecting bar

to bending perpendicular to the plane of the bilateral portion of the fixator. A multi-planar fixator may also be indicated when the primary fragments are small. When only two pins are possible in one plane, a third pin may be placed in a different plane to improve fragment purchase. Complex, multi-p lanar fixators have been criti-

cized as potentially being too rigid. They may significantly reduce the load being borne by the callus and thus reduce the stimulus for callus development and maturation. To counter this effect, destabilization of the frame should be considered once ca llus development has begun. The optimal time at Wllich to increase the load borne by the callus has not been detennined. In a large gap fracture model, s ix weeks of healing

will increase the AMI. Torsional forces are resisted by friction between the e1amp and connecting bar in a unilateral frame. Theelamp bolt must be very firm ly tightened to ensure that it is secure. If the surgeon feels that a unilateral fram e will not be able to provide sufficient resistance to the

seems most advantageous. The extent of the bone and soft tissue injury should be taken into account for each case. Destabilization is preferably achieved by removing connecting bars from a frame but can also be achieved by removing pins. Fixator frames can be constructed with acrylic or epoxy materials. They have the advantage that pins can

bending forces in a particular patient, then a more

be pos itioned in any plane; soft tissue interference can

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Manual of Small Animal Fracture Repair and Management

be minimized and wo unds can be avoided. This is particularl y helpFul for shearing injuries and for fractures of the jaw. Acrylic connections can also be used when the small metal system is too large, such as in toy breeds and birds. Polymethylmethacrylate is the most common material used. One commercial system supplies tubing and prepackaged methacrylate for connecting bars similar in strength to the small and medium metal systems. The acrylic can also be nnixed to its dough state and applied without tubing. Epoxy putty is of similar strength to the acrylics and is easier to use for small fi xators.

Points to remember Maximize pin diameter Maximize pin number per fragment Reduce pin length Add more cOIUlecting bars Reduce connecting bar span Use full pins and bilateral frames when possible.

Intramedullary pins and interlocking nails Pins Intramedullary pins provide little resistance to axial compression . If the fracture configuration is not inherentl y stable (i.e. simple, transverse), collapse will occur. Intramedullary pins are able to resist bending forc es because of the ir large AMI. They are not able to resist torsional forces and, again , must re ly on interdi gitati on of fracture frag ments to be stable as a single device. Stacked pinning increases the rotational stability only very sli ghtl y and should not be re lied upon if the fracture is not inherentl y stable. Because of these defici encies, intramedullary pinning as the only fi xa tion method is onl y indicated in simple fractures in which there is good interdigitati on of fragments. If this is not the case, adjunct fixati on must be added or another fixation method chosen. Pins can often be used for metaphyseal and epiphyseal fractures, particularly if they are placed dynamically. These fractures are often quite transverse and so they ha ve inherent resistance to collapse. Two small pins placed on either side of a fragm ent will impart rotational stability if they engage well proximally. Dynamic placement entails directing the pins into the medullary cavity and having them deflect off the inner wall of the cortex and continue up the medullary canal into the far metaph ysis. The interaction of the pin with the cortical wall provides a stable anchorage against rotational forces. The crossed pin technique can also be used: these pins begin on one side of the bone and penetrate the cortex on the other side. For optimal rotational stability, the pins should be directed so that the point at which they cross is above the fracture line.

Interlocking nails Interlocking nails resist a ll three of the forces acting on a fracture. The screws that lock the proximal and distal fragm ents to the nail prevent collapse under compressive forces and prevent rotation when torsional forces are app lied (Figure 3.9). The central location of the nail and its large AMI provide good resistance to bendin g. Interlocking nai ls are weakened at the screw holes and this weakening is not reduced by placing a screw in the hole. It is there fore important to position the nai l so that screw holes are not close to the fracture. In some situations, this ma y mean selecting a nail wi th onl y one lockin g screw. New nail systems are being developed for veterinary use. The influence of factors such as screw size, number of holes and nail diameter will need to be determined to guide the surgeon in the selection ofthe appropriate nail for each case.

Orthopaedic wire and cerclage Orthopaedic wire is malleable stainless steel that is formed into cerclage, henni-cerclage, interfragmentary or tension-band wires. The wire is often stressed during placement and tying, and is susceptible to fatigue failure. Small nicks and notches in the wire also weaken its resistance to repetiti ve loading.

t Figure 3.9: Interlocking nails provide good stability because lhe primary fraclurefragmel1ls are 'locked ' to lhe device. Compressive and rotational/orees are resisted by the screws. Because tlte naiL has a large area moment of inertia, it resists belldillg forces well.

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Biomechanical Basis of Bone Fracture and Fracture Repair Untwists Unbends ~

(b)

especially in conjunction with one or two skewer pins so that their line of action is directed more perpendicular to the fracture line. Hemi-cerclage is chosen when the cylindrical nature of the diaphysis can not be rebuilt. When used in

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conjunction with an intramedu llary pin , the wires Both unbend ~

===--

JBc::

(e)

should also encircle the pin. Interfragmentary wires are used to appose fragments in flat bone fractures, particularly those of the mandible. Twist knots are the most common.

Tension-band wires are employed to counter bending forces on pins or screws used to attach avu lsed bone

Figure 3. 10: The three COIIIIllOIl cerclage kllots. (a) ,/ivist knot. When loaded past its yield POilll, the kilO! Illltwists. (b) Single loop. Greater tension is generated thall for a {wist kllot. The loop yields at a similar load to twist kllots by the free arll1l1llbelldillg. (c) Double loop. A greater tellsioll is generated alld it resists a lIluch greater load before yield. Both arms unbend during this process.

fragments. They should be positioned opposite the direction of pull on the fragment. Although they are passive structures, the cyclic stresses are reduced if they are tightened firm ly. The wires are frequently placed in a figure-of-eight configuration and tied with one or two twist knots (Figure 3.11).

Full cerclage acts to compress fragm ents of the diaphysis together. The complete circumference must be rebuilt and fragments accurately reduced because the wire will no longer be tight ifthere is any reduction of the circumference around which they are tied. Cerclage comparisons are based on the tension that is generated when they are formed and the resistance of the knot to loosening.

Bone screws and plates

Twist knots must be formed by evenl y wrapping both wire strands around one another (Figure 3.10). This knot is used conun onl y because it can be formed with inexpensive equipment. When loaded past their yield point, the wires untwist The single loop knot is formed using a wire with a loop made in one end: the free end passes around the bone and through the loop. The wire

Screws Screws convert the torque of insertion into compression

along theirshaft. They are used individually to compress or hold fragments, or in conj unction with a bone plate. In most instances of individual use, they are applied in lag fashion so that fragments are compressed together. The near fragment is drilled to the diameter of the threads while the far fragment is drilled to the core diameter and, for most screws, threads are cut with a tap. As the screw is tightened, the head of the screw compresses the near fragment on to the far fragment. The amount of compression that can be achieved is dictated

~tl of the triceps ...

is tensioned in a wire tightener wit h a rotating

crank. Once tight, the free end is bent over, cut and fl attened. The single loop cerclage generates greater tension than the twist cerclage but has similar yield properties - the free arm unbends as the wire yields The double loop cerclage is formed from a piece of wire bent double in the middle: both ends are passed around the bone and back through the bend. Both anns are tightened using a w ire .. is countered by the tension band wire

tightener with two cranks and bent, cut and flattened in a similar fashion to the single loop cerclage. This cerclage generates three times the tension o f the single loop cerclage and resists

twice the distracting load. A minimum of two cerclages should always be used; otherwise bending forces are not countered. Long oblique fractures of two or three segments are the most suited to their use but they are not considered strong enough to be the only means of fixation of a fracture. They can be used in some shorter oblique fractures,

Figure 3.11: A tension bal1d wire is a passive structu re that resists the pull of a distracting muscle that is actillg all the \ i\.'. elld of a pill or screw. I/)

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...:!'

;:.-

.-,-

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Manual of Small Animal Fractu re Repair and Management

Thread s DO NOT engage in co rtex

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Line perpendicular to fracture lin e

I n a number of instances the screw must resist

Line perpendicular to long axis of the bone

bendi ng and the surgeon must select the appropri ate sized implant. The bending strength of a screw is determined by the AMI of its core diameter. This relationship involves raising the radius to the fourth power. A 4.5 mm cortical screw is 2.5 times as strong as a 3.5 mm screw .

Plates Bone plates are effecti ve in resisting all three of the forces that must be countered - compression, bending

Threads engage in far cortex

Figure 3.12: A screw placed illiag/ashion is used to compress two /ragmellls together. Screw threads engage the far cortex but /lot the /l ear cortex. As rhe screw is (igh/elled, compression is achieved. The optimal orielllarioli/or the screw ill sharrer oblique fractures is half way between a line drawn perpendiclliar to rhefracrure line alld a line drawll perpendiclliar to the long a.xis of the bone.

by the strength of the bone threads in the far cortex. For optimal compression, the screw is ideally placed perpendicularto the fracture line. When the fracture is short and oblique, this is not feasible and will often result in sliding of the fracture fragments. The optimal angle is then half-way between perpendicular to the fracture and perpendiculartothe axis of the bone (Figure 3.12) . (The same principle holds if skewer pins and cerclage wires are used for a similar purpose.)

(a )

(b )

and torsion. They are most susceptible to bending forces because of their eccentric position relati ve to the ax is of the bone. Their mode of placement dictates the level of risk associated with a repai r. If a fracture is anatomicall y reduced and the fragments are compressed by the plate, the bone and plate share the load, their combined AMI is large, and the construct is strong (Figure 3.1 3a) . If the bone is not reconstructed, particularl y the cortex away from the plate, the plate alone must resist bendi ng fo rces. The solid section of a plate is usuall y strong enough but if a screw hole is located within the fracture the screw hole is the weakest point. The AMI is greatly red uced and there is a concentration of stress (Figure 3. 13c). To reduce the stress concentration effect, the limited contact plate (LCP) was designed with a scalloped profi Ie to the surface that is in contact with the bone. Because the AMI is similar over the length of the plate, there is little concentrat ing effect of the stress. The solid section of the LCP is significantly weaker than the solid section of the regular dynamic compression

«)

(d)

'" 'C

··· 0S.~

" '-Complete bone contact

'" {(1

0,»

@~~

r3 ;&:; ~ .... /

Screw hole

hole

II '--

Some bone contact

No contact Plate alone

Pin supports the plate by increasing the AM I

Figure 3.13: The bending strength of a fractured bone repaired with a bone plate is affected by the integrity of the bOlle after tlie repair. (a ) If the bone is fulLy rebuilt, its dimensions call be inclllded ill the estimation 0/ the AMI at the weakest poim o/tlie repair. The bone protects the plate/rom belldillg loads. (b) I/th e/ar cortex makes comact, this will also cOllfribute 10 the AMI at the weakest poim. Because the bone comact is some distance from the plate, th is provides some mechanical advantage. (c) If there is no cOlllact between tile bonefragmellfs, the pfate mllst resist all the bending/orces. The AMI of the lVeakest point mllst be considered when assessing the stability 0/ the repair. (d) By com billing a plate with all intramedullary pill, the AMI of the comminuted area is greatly enhanced.

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Biomechanical Basis of Bone Fracture and Fracture Repair plate (DCP). LCPs rely on the presumption that, when the solid section is bearing the load alone, the bone will usuall y also contribute to the strength of the repair. If a hole does need to be left unfilled, the plate is only as strong as its weakest point and the reduced strength of the solid section will have little effect on outcome. Also, the original LCPs were made of pure titanium, which, though weaker and less stiff, has superior fatigue resistance. The scalloped contour also reduces the amount of cortical bone that is devitalized by the plate ' s interference with periosteal blood supply. Plates may still be used for repair in fractures in which it is not possible to reconstruct portions of the shaft or in which it is felt that the extensive dissection necessary to incorporate all fragments into a repair would compromise healing. Lengthening plates, which come with a range of lengths of the solid section, can be used in bones that are large enough to accommodate a 4.5 mm screw. Another approach that can be used in bones of all sizes combines a plate applied to the primary proximal and distal fragments with an intramedullary pin (Figure 3.13d). The plate effective ly prevents fragment collapse and rotation but, without the pin, the central span that is unattached to the bone is subjected to bending. By adding the intramedullary pin to the repair, the AMI of the implants is greatly increased and the risk of plate failure greatly reduced.

GLOSSARY This section gives more detail of terms highlighted in bold earlier in the chapter, in the order in which they first appeared.

percentage. Strain, like stress, is complex within complex structures and similar techniques are used to simplify their understanding. For example, if a piece of cortical bone 10 !TUn long is compressed, it will shorten as the load increases. Because we know that the failure strain of bone in compression is approximately 2%, we know that if the load applied reduces the height of our piece of bone to 9.8 mm, it will probably break.

Stiffness When a load is applied to a structure and it defonns, the relationship between tl,e load and deformation represents the stiffness of the structure. In most simple cases, stiffness is assumed to be linear and is denoted by a single number with ullits of Newtons/mm. It is represented graphically by the slope of the load versus defonnation curve. In fracture mechanics this is often an important parameter to consider: the stiffer the structure, the less motion will be present at the fracture site.

Modulus If the stress and strain are calculated for a structure that had a load versus deformation test, the slope of that curve is termed the modulus. It denotes the stiffness of the material, in contrast to the stiffness of a structure. Its units are the same as stress - Newtons/mm' or Pascals. Modulus is useful for comparing materials and making assumptions about how structures might behave based on their material. An example would be the comparison of a bone plate made of stainless steel versus one made of titanium. The modulus of steel is greater than tl,at of titanium; so, for a similar load and given that the plates have the same dimensions, there would be less movement with a steel plate.

Isotropic and anisotropic Stress When an external load is resisted by a structure, internal forces are generated. These internal forces are termed stress. In complex structures with complex forces (such as bones), the stress is also complex. Two approaches are used to simplify the understanding of stress. The forces can be simplified to a single important direction or the stresses can be considered only in certain important directions. One important point to remember is that stress is distributed over the cross-sectional area of a stmcture, and so the magnitude at anyone point will be influenced by this dimension. The usual units for stress are Newtons/mm' CN/mm') or Pascals (pa).

Strain When an external load is resisted by a structure, the structure defonns. Often, the internal defonnations that compound to produce the overall change in shape must be considered. These internal defonnations are termed strain. Because they describe deformation within a material, they are expressed as a ratio of the change in length to the original length; the usual terminology is

If a material is homogeneous, the expected response will be the same, no matter what is the direction of the applied load. This material is isotropic. The steel of

implants is isotropic. When a material or a structure has a direction in how it is put together, its response to a load will depend on the direction from which the load is applied. This material is anisotropic. Most biological materials are anisotropic and to appreciate the properties of the material fully it is important to denote its orientation relative to the forces impacting it.

Shear Shear is generated when an applied force causes two parts ofthe structure to want to slide past one another. This is most easily demonstrated at interfaces between two objects when one goes one way and tlle other another, but is also present within a stmctiire when the base is held firm and the top is pushed. Shear can refer to a way in which a force is applied and to tl,e types of stress that are present within a material. Shear stress is created when torsional forces are applied to bone.

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Area moment of inertia Area moment of inertia (AMI) is a structural param eter important in assessing resistance to bendin g. It quantitates not only the cross-sectional area, but also ho w the material is distributed. In pure compression or VetBooks.ir

tension, cross-sectional area alone provides an estimate of a stru cture's strength. In bending, one s ide of

a structure experiences tension and the other compression . There is a plane along the structural centre that ex peri ences no force; tllis is termed the neutra l plane. Material further from the neutral plane is better able to resist the forces in the structure, and so the fo rmula e for calculati on of this parameter emphas ize this distance. For a circul ar structure, the formula is (n .r')/4 , w here r is the radius. The influence of increas ing the diameter on a structu re's abili ty to resist bendin g is easil y appreciated. For a rectangular stru cture, the equation is (b.h3)/ 12 , where b is the width and It is the height. Because the terms width and height relate to the orientation of the rectangle re lative to th e bendin g

force, it is important fi rst to determine in which directi on bending will occur before computing this parameter. For example, a 3.5 mm bone plate (10 x 3 mm) on

the lateral aspect of the femur would be ex pected to fa il in medi olateral bending before crani ocaudal bending, because the AMI in the mediolateral directio n is 29.9 mm' and in thecrani ocaudal directi on is250 mm' . It is also important to realize that AMI is influenced by the plane chosen in measuring the dimensions. When analysing an implant o r fracture repair, consider the weakest po rti on. Using the 3.5 mm bone plate example, the AMI in th e medi olateral direction th rough a ho le is only 14.8 mm'.

Polar moment of inertia Polar moment of inertia is a similar concept to area moment of inertia except th at it defines the dim ension

of a structure at a certain plane relati ve to its ability to resist torsio nal forces. Tllis parameter quantitates th e way in which th e structure is distributed around th e centre of the torsional effect. This is obvio us ly easy for

circular structures but becomes more complex with complex shapes. For a hollow cylinder (li ke a bone) be ing twisted around its longitudinal ax is, the equatio n is '/2 .n.(r' - 1"'), where r is the outer radius and r' is th e

inner fadi us.

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CHAPTER FOUR

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Fracture Healing Tim M. Skerry

INTRODUC TION

Wounding

Fracture healing is a speciali zed fo rm of wound repair in which there is regeneration of the injured issue without scar formation. The mechanisms behind such a remarkable response involve bone growth, modelling and remodelling. The control of fracture repair therefore in volves the same loca l and systemic influences capable of affecting bone in other circumstances. The purpose of this chapter is to provide a brief introduction to the cellular processes that are acti vated when bone fractures, and to explain: The implications of concurrent injury, disease or treatment on the progress of a healing fracture The mechanisms behind the novel treatments for enhancement of healing which are begitming to appear in the clinics.

ACUTE EVENTS AFTER BONE FRAC TURE In addition to the local events that occur immediately after fracture, there is an acute inflammatory response to the injury. The major systemic effect of this inflammation is the acute phase response (APR), a process that appea rs to have a protecti ve fun ction for the organism (for reviews see Lewis, 1986; McGlave, 1990). Local inflammation associated with injury causes changes in the circulating concentrations of the acute phase proteins. These include proteins with coagulation and complement system functions, their inhibitors, transport proteins and C-reacti ve protein . The APR is also associated with changes in hormones (insulin, glucocorticoids and catecholamines), vitamins and minerals - primarily iron and zinc. There is also acti vation of proteolytic enzyme cascades connected with clotting, complement, kinin and fi brinolytic pathways, and a change in amino acid metabolism, with breakdown of muscle protein. Locally, the acute events after fracture follow the same initial sequence seen in other tissues, with bleed-

Coagulation Platelets PDGF TGF ~

ECF (TG Fo.)

Inflammation

(

Acute Phase Response IL-1 IL-6

IFGy

Lymphocytes TGFp IL·2 IL·S

Repair Fig ure 4.1 The inflammatory cascade. The consequences oj injury include tile dijferellf stages of the inflammatory process ;n which are expressed mOllY a/the same cytokines as those with effects 011 bone physiology.

ing, progressing through organization of tbe clot, angiogenesis and fibrosis. At this stage, events in bone begin to differ from other tissues, as the fibrous callus is replaced by cartilage which undergoes endochondral ossification and eventually remodelling. It is important to consider the mechanisms of these acute changes, because the so-called inflammatory cytokines (Figure 4.1) are in many cases regulators of normal bone fun ction (Table 4.1 ). This is entirely in accordance with the needs of an earl y inflammatory response to injury. However, persistent inflammation (as a sequel to infection, for example) may cause aberrant or inappropriate effects by direct actions on the cells that are attempting to repair the fracture.

TYPES OF FRACTURE HEALING Indirect fracture healing In normal circumstances after a fracture, there will be some degree of instability of the bone ends. The movement between the bones will not support imme-

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Cytokine

Osteoclast formation/activity

Osteoblast growth/activity

Resorption ill vivo

Formation in vivo

IL- I ~

+/ +

+/ -

TNFu

+ /+

+ /-

IFNy

-/ -

IL-6

-/-

-/ -/-

GM-CSF TGF~

+/+

-/-/-

FGF PDGF

Ta ble 4. 1: Cyrokilles implicated ill bone formation (Ind resorpliol1. Mas! of the cytokines ill rliis table are also implicated ill (lie

illjlallll/1atOlY response, showing rite pleiotropic actiolls of these agents. The compLex actions oj cytokilles are iilustrated by the divergence between actions of illdividual age Ills all specific cells in vitro, seell as - which denotes differem results by di/ferellf workers. /" additioll, the fack a/correlation ber-ween in vitro {md in vivo actiolls, or stimulatioll a/both/ormation Gild resorpri all by a sillgle agent, suggest tltat the p icture presellfed by these data are far /rolll complete. + = expression; - = 110 expression; space = 110 data.

diate formation of new bone, and a tissue with the ability to deform more than bone must be made as an intermediate. Fibrous tissue is therefore produced by fibroblasts in the organizing clot aro und the fracture. In the orga ni zation process, capillary invasion and angiogenesis occur so that the clot becomes accessible to other precursor cells via the circulation. The fibrous tissue stabilizes the fracture enough to permit cartilage surviva l, and a wave of metaplasia passes fro m each side of the periosteal cuff of the ca llus ac ross the fracture gap. The cartilage is then replaced by bone in endochondrial fas hion. Biologicall y, this indirect fracture hea ling is a sensible process. Since the clot forms a mass aro und the fracture site, the ensuing callus fo rms a large cuff around the bone enels so that, as the organization process occurs, the sequential stiffening of the tissues provides good mechanical stability. When the bones have uni ted, the fracture is stronger than the surrounding norma l bone, and remodelling (see below) reduces the superfluous mass so that eventually complete restoration of normal function and strength can occur.

ble for trabeculae to regenerate directl y. This can occ ur by axial growth of new elements along collagen alld elastin fibres which form within the defect (Aaron arlei Skerry, 1994). Direct fracture healing does not occur witho ut surgical intervention. The ASIF developed the ideas th at anatomical reduction, rigid fi xation and rapid return to normal function were the ideal goals of treatment (see Chapter 9). In many fractures, perfect anatomica l reduction is not necessary for good function, and ri g id fi xation can have adverse effects on the rate of healin g. Fractures flXed with plates, which heal by direct unio n, are wea ker than the surrounding bone and take mu ch longer to unite than those that heal by indirect union. It is tempting to assemble the 'jigsaw' in order to obtain a satisfactory postoperati ve radiograph, but the reducti on of use of plate fi xation in human orthopaedics, and tlle increase of use of intramedullary nai ls and extern al fixators, implies that other considerations may be more important (see Chapter 10).

Direct fracture healing

FRACTURE REPAIR, BONE GROWTH AND REMODELLING

There are circumstances in which the presence of fracture ca llus is a serious obstacle to a return to function. This is rarely the case in midshaft fractures of long bones, but where a fracture incl udes part of an articular surface, rapid anatomical realigrunent of the fragments is the primary consideration. If this is perfo rmed and the fragments are held ri gidly, direct frac ture healing can occur with littleornocallus fo rmation. In this circumstance, Haversian systems can cross the fracture gap and repair the cortical bone directl y without any endochondral processes. Where defects exist in cancellous bone, with sufficient stability, it is possi-

When the processes in vol ved in fracture repair a re dissected into their component parts, there are man y similarities with bone growth and remodelling (Tab Ie 4.2) . In both growth and fracture repair, endocho 11dral ossification occurs to convert a minerali zed cartilage template into new bone tissue, using th e same regulated chondrocyte differentiation pathwa y. Because of these similarities, understanding of fra cture hea ling is simpli fied if the controlling influenc es of the indi vidua l component processes are considered separate ly.

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Growth (endochondral)

Growth (apposition)

Remodelling

FractUl'e I·epair

Chondrocyte differentiation

Cartilage resorption

Bone formati on

Bone resorption

Table 4.2: Similar component cellula r processes are comhi/led differently to give rise to such diverse tissile actiolls as longiTudinal hone growth Qlldjraclllre healing.

Endochondral ossification and appositional growth During the no rmal endochondral ossification process, chondrocytes in the growth plate undergo an ordered developmental sequence. Chondrocytes in callus, prob· ably originating from cells within the periosteum or from differentiating cells in the organi zing haematoma, undergo th e same sequence of events. After mineralizati on of carti lage, there is capillary

invasion and recruitment of cells resembling osteoclasts. Since they resorb cartilage, not bone, they are termed chondroclasts, but there is no evidence that they are a separate cell type. The cells resorb crescent-shaped pieces of calcified cartilage matri x, analogous to the Howships' lacunae resorbed from bo ne by osteoclasts. New bone is then fonned in those defects. New bone formation at this stage is similar to the appositional formation that occurs with periosteal expansion durin g growth. Mature osteoblasts line the surfaces, and secrete matrix in a highly polarized fashion , so that it is deposited on the s ide nearest to the bone. This hi ghly regulated polarization is controlled by specific cytokines and moderators of their functi on at diffe rent levels in the periosteum. For example, transforming growth factor 6 (TGF6) is ex pressed by osteoblasts on th e bone surface and in a more periphera l zone two or three cell layers further away from th e surface. Interestingly, the zone between th ese two layers does not contain TGF6, and in th e more periph eral zone the act ions of th e peptide are moderated by expression of the latent TGF6-binding protein, which is absent on the bone surface. The new bone matrix differs from carti lage in that the predominant collagen is type I (type II is the predominant fibrill ar collagen in carti lage), although th e same chondroitin sulphate and some keratan sulphate proteoglycans are also present. Mineralization of this osteoid proceeds with focal calcifications occurring around matrix vesicles. While most osteoblasts advance with th e deposition of matri x, some remain and become incorporated in the new boneasosteocytes. It was tho ught that this was a passive process. However, durin g the development of fi sh bone, all the osteoblasts continue to advance with th e periosteal

surface, so that no osteocytes are formed. This suggests that mammalian osteocytes are osteoblasts that made a committed step to stop advancing by substituting polarized secretion with a generali zed secretion of matri x proteins. Bone fonnation during fracture healing, whether endochondral or appositional, results in replacement of the large mass of the soft periosteal and endosteal callus wi th bone. However, atthisstage,although there is restoration of function in that the bone is ab le to withstand loading, the mass of th e callus is excessive. In addition, the bulk of the callus may interfere with norm al muscle and tendon movements . To convert the relatively disorgani zed bony callus into a restored cortical tube, the callus must be remodelled - a process entailing bone resorption.

Bone resorption and callus remodelling Bone resorption is accomplished by osteoclasts, which must perform two roles: removal of th e hydroxyapatite mineral phase of th e bone wi th acid; and degradation of the collageno us and non-collagenous proteins with enzymes. Osteoclasts are hi ghl y polarized cells that initiate resorption after attaclling to the bone surface at the peri phery of th eir zone of contact. This sea ling or c lear zone contains contractile proteins including osteopontin, which are secreted by the osteoclast to faci li tate attachment. Osteoclast attachment to bone matri x is also facilitated by integrins - a class of cell matrix attachment mo lecules found in many tissues. Interestingly osteoclast attachment is mediated by an a.V63 integrin, whose 63 s ubunit appears to be exclusive to these cells and is different from the 62 s ubunit ex pressed by closely related cells of the monocyte macrophage lineage. This specificity may have therapeutic implications, as neutralizing antibodies to the osteoclast integrins inhi bit bone resorpti on (Horton et aI., 1991). Tight attaclunent allows the osteoclast to maintain specific conditions in the resorption space where the pH may drop as low as 3 (Sil ver et al. , 1988). Acidification of the resorpti on space is the res ult of secreti on of hydrogen ions, prod uced by the action of carbonic an hyd rase and transported across the osteoclast's ' ruf-

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Manual of Small Animal Fracture Repair and Management

fled border' cell membrane by a specific proton pump. This appears to be uniquely expressed in osteoclasts and different from the classical vacuolar and potassium ATPase pumps found in other cells. A chloride! bicarbonate exchanger in the basal membrane of the cell maintains the osteoclast's intracellular pH, which wo uld otherwise rise with acidi fication of the resorption space. Degradation of matrix proteins is accomplished by neutral protease enzymes such as cathepsins, which are secreted into the resorption space.

Bone resorption in remodelling is responsible for remova l of the now superfluous mass of periosteal and endosteal callus. At the same time, Haversian remodelling occurs in the intracortical callus to restore normal compact bone structure.

Haversian remodelling is an ordered process of bone resorption and formation within the cortex, which gives the classical histological appearance of concentric lamellae inadult bone. It is importanttodistinguish this from the primary osteonal bone seen in yo unger animals, which is a feature only of rapid growth and not previous resorpti on. Primary osteons arise w hen a periosteal bone sur-

face expands rapidly in young growing animals. The osteoblasts in periosteum form osteoid matri x, as de-

scribed previously, but in an irregular way so that some areas of the advancing front proceed faster than others. The conseq uence of this is that gaps lined with osteoblasts are left in the new bone surface and these fi ll in concentrically. Primary osteons are therefore characterized by concentric lamellae of bone, which do not interrupt the more linear lamellae that represent the line of the advancing mineralizing front (Figure 4.2). In appeara nce they are not dissimilar from knots in wood.

.. . ....... ... . ..... ........

,- 6 \.

3 2

... - .... - ...

lae of the Haversian system cut through the preex isting lamellae of the bone.

Increased understanding of the control of bone cells and the way that loca l interactions occur has led to some exciting new ideas w ith direct relevance to the

clinician. The idea of using biological materials to enhance fra cture healing or to stimulate filling of defects has progressed beyond bone graftin g, and may explain some of the mechanisms by which that technique can be so effecti ve. Experiments have shown the profound effects of deminera lized bone matrix in stimulating bone fonnation ill vivo (Syftestad et aI., 1984), and this appears to be due to stimulatory effects of some of the extracellular matrix components as well as mitogenic growth factors such as the insulin -like growth factors, transforming growth fac tor B (TGFB) and the bone morphogenetic proteins (BMPs) which are present in large quantities in bone. Direct application of exogenous TGFB or BMPs have been shown to stimulate profound bone formation in hea ling fractures (Bolander, 1992). The actions of these agents may be related to their roles in development, where limb morphogenesis is linked to BMP ex pression (Jones et al., 1991). Such therapies are not confined to the laboratory. Growth factor-loaded bone cements and bone substitutes are in development for clinical use, and may offer radical advances for treatment of inactive non-unions, where bi ologi-

continue to resorb bone, so that in cross-section a Haversian system, like a primary osteon, contains concentric lamellae. However, the concentric lamel-

ENHANCEMENT OF FRACTURE HEALING

Haversian remodelling

Secondary osteon s or Haversian systems are suo

perficially similar to primary osteons, but arise when a group of osteoclasts tunnel into a surface and proceed along the length of the bone (Figure 4.3). At the same time as the tunnelling is proceeding, capi llary growth occurs to maintain supplies to the cells, and to bring in osteoblast precursors. The osteoblasts fill in the tunnel concentrically as the osteoclasts

-..

-.~.

-'--

.....

cal activity has ceased. Finally, it is appropriate to consider mechanical loading as a method of effecti ng fracture healing. Bone cells are rapidly res ponsive to strain in the matrix (Skerry et aI., 1989), and interfragmentary movement has been shown to stimulate more rapid progression of indirect healing than totally rigid fixation (Goodship and Kenwright, 1985). It is of extreme importance to distinguish these micromovement re-

Figll re 4.2: As osteoblasts appose new bone 011 a periosteal sllrface, primary os/eolls result from concentric infilling of spaces left as the developingjront of/ormation advances unevenly. The lamellae between the primary osteons are continuous and are not imerrupted by the osteollS. Numbers show fhe order of deposition of lamellae.

gimes from the gross movements that occur at inadequatel y fixed fracture sites. The latter will not enhance hea ling! The use of controlled micromovement has become accepted to the degree that fixators are now dynamized to allow small movements at the fracture

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Fracture Healing

-A ____ ------ -------- __ _ ------ ~ ------------------------

~~----

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-------

- S --- - - - - --------- - - ---- -------------------'Cutting co ne' of osteoclasts

Osteoblasts laying down.~::::==-_ _+:-'I:-~ new bone :::

New osteocytes embe dded in

bone matrix

- - - - --.¥::t:(

Surface lining ce lls ------++,i.!.-::::c::~

-':;';~=\=;t:::::'" Classical co ncentric lamellae of Haversian

bone

Figure 4.3: Cel1lrai figure: Haversian or secondary osreolls are the result of tUl1nelling ilUO the bone cortex by a 'cutting cone' composed of osteoclasts. immediately behind the osteoclasts, populatiolls of acti ve osteoblasts lay dOlVll llCIV bone Gnd graduaiLy become less active as Lining cells which cover the swiaee. Some osteoblasts becollle incorporated illra the new bone matrix as osteocytes. (A)-(C) Cross-sections show progressive expansion oflhe resorbing Haversian cGnal as the clltting COile 0/ osteoclasts erode oul a/the plal1e o/the diagram. (D) - (F) Osteoblastsjill in the defect, resulting ill the classical cOllcentric lamellae o/secondarily remodelled Haversian bOl/e. These lamellae interrupt the original lamellae a/the primary bone.

site, in order to stimulate the cells and enhance the healing_Recent research into the earl y consequences of loading on bone cell gene expression has already led to the identification of a number of possible pharmacological targets which could mimic the effects of loading in situa ti ons where the application of

movement is imprac tical. The discovery that bone cells communicate via exCitatory amino ac ids, previ-

ously thought to be involved onl y in intercellular communication w ithin the eNS , is one example of a route by which the healing of fractures might be enhanced (Mason et at., 1997).

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CONCLUSIONS Fracture hea ling is a remarkable process in that it is one of the most successful repair mechanisms in the body. When one considers the immense complex ity of the cel lular interactions thatoccurto restore the continuity offractured bones, it is surprising that so few problems occur. Increased understanding of the fundamenta l physical and biochemical influences on bone is having a considerable im pact on clinical treatments, and will continue to do so. The relative ease of production of recombinant osteotropic biochemicals and the development of novel methods of app lication and delivery mean that fracture treatments are likely to advance beyond recognition in a short time. Since technological advances invariably appear to exceed predictions, the only certainty about the future is that it wi ll be even more exciting than anytiling which is currently perceived to be possible.

REFERENCES AND FURTHER READING Aaron JE and Skcrry TM (1994) Intramembranous trabecu lar gcnern~ tion in normal bone. BOlle alld MilleraI25(3), 211. Bolander ME (1992) Regulat ion of frac ture repair by growth factors. Proceedillgs ofthe Societyfor E:cperimelluli Biology and Medicine 200, 165. Currey JD (1984) What should bones be designed to do? Calcified Tissue IllIernalional 36(S I), 7.

Goodship AE and Kenwright J ( 1985) The innuence of induced micromovemelll upon the healing of experimental tibial fractures. JOl/rnal oj BOlle alld Joilll Surgery 678, 650. Horton MA, Taylor ML, Amell TR and Helfrich MH (1991) Arg-G lyAsp (RG D) pcptides and the anti-vitroncctin receptor antibody 23C6 inhibit dentine resorption ,lIId cell spreading by osteoclasts. £rperimellw/ Cell Research 195, 368. Jones eM, Lyons KM and Hogan BLM (199 1) Involvement of bone morphogenetic protein-4 (BMP-4) and Vgr-I in morphogenesis and ncurogcncsis in the mouse. Deve/opmelll Ill, 531. Lewis GP ( 1986) Mediators of IlIjl(//lIl11atioll , Wright, Bristol. Mason DJ , Suva U, Gencver PG et al. (1997) Mechanically regulated expression of a neural glutamate transporter in bone. A role for exci tatory amino acids as osteotropic agents. BOlle 20, 4-9. McGlave P ( 1990) Bone marrow transplants in chronic myelogcnous leukaemia: an overview of determinants of s urvival. Semillars ill HaelllGtology 27, 23-30. Nathan CF and Spom M8 (199 1) Cytoki nes in context. Journal oJCel! Biology 113, 98 1. Rosat i R, Homn GSB, Pinero OJ et al. (1994) Nonnal long bone growt h and dcvelopmen t in type X co llagen-null mice. Namre Genetics 8, 129. Silver lA , Murrills RJ and Etherington DJ (1988) Microclectro- -.-,

Greater tuberosity

A )) J7

~ O!::':: O f-/7

Caudal view

Proximal or

external fixator

region

Supratrochlear foramen t~1 (a) \ ......

Two-pin unilateral uniplanar

mid shaft

\r r-

t::;:~(Medial

......

Caudal View

~ Distat { third

--1~ \k '

Greater rW~ tuberosity

Alternative position for distal pin

condyle

Figure 15.20: (a) Intram edullary pin positioning ill humeral shaft fractures. (b) Extemaljixator used to minimize

rotation/allowing intramedullary pinning.

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Lateral view

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184 Manual of Small Animal Fracture Repair and Management

OPERATIVE TECHNIQUE 15.5 (CONTINUED) VetBooks.ir

Intramedullary pinning: humerus

The a lte rnative method of pin introduction is retrograde pinning. The pin is driven up the shaft from the fracture site, kee ping the shoulder flexed and the pin directed towards the lateral side of the greater tuberosity. Once the tip of the pin has emerged, it is grasped with th e Jacobs chuck and drawn up the shaft suffi cientl y to pennit reduction of the fracture . Reduction is maintained with the bone holding forceps wllile the pin is dri ven into the distal shaft. The position of the fracture influences the length of pin required. For fractures involving the proximal or mid-shaft region, the pin is dri ven down the shaft to a point just proximal to the supratroc hlea r forame n (Figure IS .20a). For fractures involving the distal third, a sma ller diameter pin is used. The pin should be directed towards the medial side of the shaft so the tip bypasses the supratrochlear foramen and is embedded in the medial condyle (Figure IS .20a). When the pin has been inserted to the correct de pth, it is broke n off flush with the bone. If it has not already been pre-cut, the pin is c ut with pin cutters (or a hacksaw) just proximal to the tuberosity. A two-pin ullilate raljuniplanar external fi xa tor (Fig ure lS .20b) can be used to supple ment the intramed ullary pin to mjnjmize rotation and the ris k of non-union. Alternatives to the extemal fixator for preventing rotational instability following intramedullary fixation include cerclage and hemi-cerclage wires or stack pinning. WOlllU[

Closure

As for Operative Teclmique IS.3. If exte rnal fixation pins have been placed, th ey are clamped to the ex ternal connecting bar and routine wound closure is undertaken.

Post-operative Care

Exercise restriction until fracture union is complete. The fixator is removed after about 3 weeks, before proble ms with soft tissues are encountered. The intramedullary pin can then be removed once fracture healing is comple te. Pre-cut pins in cats often remain in situ but in dogs the pins eventuall y have a tendency to nli grate dorsally because of the looser pin fit. If this happe ns, the pin is easi ly removed .

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OPERATIVE TECHNIQUE 15.6 VetBooks.ir

External fixation: humerus

Pre-operative Considerations The humerus is surrounded by muscle and, with the exception of two small areas on the proximal and distal ends of the bone (Figure IS.21), there are no safe corridors for the introduction of the pins (Marti and Miller, 1994). Transfi xion of large muscle masses by pins results in pain and stiffness due to muscle fib ros is. In addition, pin tract infections are more likely to occur. These problems can be minimized by using a standard craniolateral approach to the fracture. Once the fracture is aligned the pins can be introduced either through the main incision or, preferably, th rough stab incisions close to the main incision. The pins are then directed between muscle bellies, avoiding

suitable for positioning of external fixator pins

the radial nerve, and are dri ven into the bone, penetratin g both corti ces.

Lateral

view

frJ~ "'-:::/

Figure 15.21: Enemal fixaror: safe areas/or pin illfroc/uctioll. (After Marli and Miller, /994.)

Positiollillg Lateral recumbency - restraining band placed under axilla and secured to tabletop to help with traction. Tray Extras Appropriate external fi xator set; pin cutters; variable-speed drill ; chuck; pointed reduction forceps; bone holding forceps; drill bits and tissue guards if pre-dri ll ing pin holes. S urgical Approach A craniolateral approach is used as described in Operative Technique IS. 3. Reduction lind Fixation In comminuted fractures of the diaphysis, the intact shaft on either side of the comminuted area is grasped with self- lockin g bone holding fo rceps. Traction is exerted until satisfactory length and alignment of the bone are achieved. The fracture site is disturbed as little as possible, with the fragments being left ill situ (see Chapter 10). A unilateral external fixator is applied to the craniolateral surface of the bone generall y with three pins in the proximal fra gment and two in the distal fragment. The di stal pin is placed fi rst. If the distal segment is very short then the pin is placed in the transcondylar position; this pin can be safely introduced through a stab incision over the condyle (Figure IS .22a) . If the distal segment is long enough, the pin can be placed just prox imal to the supratrochlear foramen but this should be done as an open approach so as to identify the radial nerve (Figure IS .16b). The most proximal pin is placed just distal to the greater tu berosity (stab incision). Five clamps are placed on a connecting bar. The proximal and distal clamps are attached to the pins already in place (Figure IS .22b). Fracture alignment is re-checked and, once it is satisfactory, the clamps are tightened to maintain reduction. The three centre pins are then dri ven into the humerus, using the clamps as guides (Figure IS .22c) .

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OPERATIVE TECHNIQUE 15.6 (CONTINUED) VetBooks.ir

External fixation: humerus

PRACTICAL TIP The three central pins are introduced through the main incision or stab incisions adjacent to it, allowing the pins to be safely guided between muscle bellies into the bone. Final adjustment of the clamps is made and the wound is closed. In potentially infected grade 2 or 3 open fractures, after thorough wound debridement and application of the fi xatorthe wound is only partially closed to allow drainage. 2

Placement of distal &

proximal pins

Alternative

location for most distal pins

Placement of remaining pins

Attachment of connecting bar with clamps

view

1 (b)

(a)

(e)

Figure 15.22: Extemalfixator llsed;11 open Gild commillllfedJractures. WOUlld Closure As in Operati ve Technique 15.3.

Post-operative Care Exercise restriction while fixator is in place. Check the frame at weekly intervals to ensure that clamps and/ or pins ha ve not loosened and that pin tract infection has not occurred. A loose pin is accompanied by an increase in pin tract discharge and lameness. Replace or remove the pin if necessary. Radiography at 4 and 8 weeks. Remove fixator once healing is complete.

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OPERATIVE TECHNIQUE 15.7 VetBooks.ir

Supracondylar fractures of the distal humerus

Positioning Dorsal recumbency, with the fractured leg pulled cranially.

Assistant Yes. Tray Extras Appropriate intramedullary pins; K-wires; wire for cerclage; pliers/wire twisters; pin/wire cutters; drill ; chuck; self-locking bone holding forceps; pointed reduction forceps. Sllrgical Approach A medial approach is used to expose the fra cture (Operati ve Technique 15.4). WARNING Protect the median a nd ulnar nerves. The skin incision should be made towards the caudal aspect of the elbow to allow skin to be reflected fro m both sides of the joint.

Redllctioll alld Fixatioll The humeral condyles are grasped with pointed reduction fo rceps; the distal humeral shaft is held with self-locking bone holding forceps; the bone fragments are tilted caudally, toggled against each other, and then pushed cranially until reduction is achieved. If there is a medial oblique supracondylar fragment, small pointed reduction forceps can be used to hold this fragment in reduction with the shaft (Figure 15.23).

Intramedu llary pin

Having checked that reduction is possible, the fracture site is hinged open to expose the medullary cavity of the medial supracondylar ridge. An intramedullary pin is retrogradely introduced into the cavity and directed laterally up the humeral shaft to emerge on the lateral side of the greater tuberosity. The Jacobs chuck is then attac hed to the proximal end of the pin, which is pulled up until just the tip is visible at the fracture surface. The fracture is reduced and then, with the elbow extended, the pin is driven down into the medial condyle. Finally a K-wire is driven up through the lateral condyle obliquely across the fracture and into the medial cortex of the humerus (Figure 15.23). This second point of fixation prevents rotation. Both pins are cut close to the bone after insertion. Skeletally immature animals In skeletally immature animals, the medial cortex is usually fractured obliquely and a lag screw or Kwire can be placed proximal to the growth plate. Crossed K -wires are then inserted to complete fixation (Figure 15.24).

Figure 15.23: Supracondylar fracrure a/the humerus: fixation using an intramedullary pin and K-lVire,

Figure 15.24: Post-operative radiograph of tile case shown in Figure 15.8: three K-wires have been used/or fixation.

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OPERATIVE TECHNIQUE 15.7 (CONTINUED) VetBooks.ir

Supracondylar fractures of the distal humerus

Wound Closure The deep brachial fascia, subcutaneous tissue and skin are closed in layers. Post-operative Care Exercise restriction until fracture healing is complete and pins can be removed.

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OPERATIVE TECHNIQUE 15.8 VetBooks.ir

Lateral condylar fractures

Positioning Latera l recumbency - restraining band placed under axilla and secured to tabletop to help with traction. Assistant Optional. Tray Extras Appropriate sized bone screw set, drill bits, etc.; K-wires; pin/wire cutters; drill ; Gelpi self-retaining retractor; pointed reduction forceps; Vulsell um forceps. Surgical Approach A skin incision is made directl y over the lateral condyle. The lateral head of the triceps muscle is exposed and the deep fascia along its cranial border is incised (Figure 15.25a). The muscle is retracted to expose the fractured condyle (Figure 15.25b).

Lateral

head of Triceps m.

Extensor carpi Incision

into fascia

radialis m.

,\)(!.~\'P'---7""Anconeus II m.

Com mon digital

Ulnaris

extensor m. Lateral digital extensor m.

Figure 15.25: Su rgical approach/or exposure in/oterol cOlldylar fractures.

WARNING The radial nerve emerges between the lateral head of the triceps and the brachialis muscle just proximal to the incision, but provided dissection is limited to the soft tissues over the lateral condyle and its supracondylar ridge there should be little risk of nerve damage during exposure. Using a periosteal elevator, any remaining muscle attac hments are cleared from the adjacent surfaces of the fractured supracondylar ridge. The condyle is then rotated laterall y to allow removal of haematoma and granulation tissue from the intercondylar fracture site. Reduction mul Fixation The simplest method of reducing the condyle is to exert pressure on the condyle with finger and thumb and then maintain reduction with pointed reduction forceps (Figure 15.26a). The lateral condyle does have a tendency to rotate caudally and application of Allis tissue forceps across the fractured supracondylar ridge helps to prevent this (Figure 15.26b). Alternati vely, a K-wire can be used (Figure 15.26c,d).

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OPERATIVE TECHNIQUE 15.8 (CONTINUED) VetBooks.ir

Lateral condylar fractures

o Lateral view

Allis tissue forceps

Caudafview

Kirschner wire placed across supracondylar ~~=f'=t ridge

(a)

(b)

Figure 15.26: Methods ofmaintaining reduction oflateral condylar fractures during insertion ofthe transcondylar lag screw.

A transcondylar lag screw and anti-rotational K-wire are used for fixatio n. There are two methods of preparation of the dri ll hole for the transcondylar lag screw: outside-in, or inside-out. Outside-in method After reduction of the condyle, th e drill ho le for th e transcondylar lag sc rew is commenced from a point immediately below and just in front of the most prominent point on the lateral condyle and is directed at the corresponding spot on the medial condy le (Figure IS.27a). A cortica l screw is us uall y used; and with this type of screw, the hole in the late ral condyle must be overdrilled to the same diame ter as the screw to enSure that the lag effect is achieved as th e screw is tighte ned, giving compression of the fracture site (Figure IS .27b,c). In very yo un g puppies with soft bo ne, a partially threaded ca ncellous screw is used fo r fixation . With this type of screw, onl y a transcondylar pilot ho le is drilled. Provided all the threads of the screw grip in the medial condyle, th e lag effect will be achi eved (Figure IS .27d).

Position of Kirschner wire -----1f-:-El

Drill guide

1=~

Partially threaded cancellous

Cortex

Position of drill hole

(a)

Lateral view

(b)

Z . (c)

(d)

Cranial view

Figure 15.27: Lag screw fixation of lateral cOlldylar fractures (see text for details).

Inside-out method This is the most accurate. After exposure of the fracture site, completely rotate the lateral condyle out of the incision on its collatera l ligament to allow ex posure of the fractured trochlea surface. The glide hole forthe screw can then be accurately drilled " inside-out' , starting in the centre of the fractured trochlea and drilling from this point to the lateral surface of the lateral condyle (Figure IS.28b). The appropriate sized drill sleeve is introduced into the glide hole from the lateral side and the condyle is rotated back into position. A K-wire can now be placed across the supracondylar fracture to maintain reduction and prevent rotation while the lag screw is inserted (Figure IS.28c). The glide hole has already been prepared in the lateral condyle and the drill sleeve is ill situ. Next, the smaller drill bit, which will be used to prepare the pilot hole, is passed through the sleeve and used to drill the pilot hole in the medi al condyle (Figure IS.28c). Length of screw is assessed with a depth gauge, a thread is cut in tile pilot hole with a tap (unless a self-tapping screw is used) and then the appropriate size screw is inserted. The K-wire in the supracondylar portion of tile fracture is c ut off flush with the bone. It is important to have this second point affIXation to prevent rotation of the condyle on the screw (Figure 15.28d).

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Lateral condylar fractures

Cranial view

Collateral ligaments

Fig u.re 15.28: 'Inside-out' method a/preparing transcondylar screw hole. (a) Fractured condyle. (b) Condyle rotated out lateralLy 011 collateral ligament; glide hole drilled / rom medial to lateral. (e) Fracture is reduced Gild stabilized with a Kwire; drill sLeeve is inserted ill gLide hole to allow accurate placement of pilot hole through medial condyLe. (d) Postoperative radiograph a/fracture shown ill Figure IS./O:fixation with transcol1dylar fag screw (4.5 11111/ cortex screw) plus

K-wire across supracondylar fracture line 10 prevent rotation of the condyLe.

PRACTICAL TIP Provided the fracture of the supracondylar ridge is accurately reduced, it can be assumed that "eduction of the intercondylar fracture is also adequate. Wound Closure The deep fascia, subcutaneous tissue and skin are closed in layers. Post-operati ve Care A support bandage is applied for 5 days. Movement of the joint is important following repair of any articular fracture - to minimize stiffness and encourage nutrition and healing of articular cartilage. Gentle passive fl exion and extension of the joint and controlled exercise should be reconunended. Restrict exercise to 10minute wal ks on a leash only for 4 to 6 weeks. Implants are generally left ill situ.

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OPERATIVE TECHNIQUE 15.9 VetBooks.ir

Medial condylar fractures

Positioning Lateral recumbency with affected leg down. The upper fo relimb is pulled well caudally.

Assistant Opti onal. Tray Extras As for Operative Technique 15.8. Surgical Approach As for Operati ve Technique 15.4. Reduction and Fixation The comments for lateral condylarfractures apply here also. However, the medial f ragment

is often large enough to accept two lag screws placed from medi al to late ral; one transcondylar and one proximal to th e supratrochl ear foramen (Figure 15.29a,b).

Figure 15. 29: (a) Pre-operative radiograph of 4-year-old German Pointer with media l cOlldyiar fracture. (b) Follow-up rad iograph taken 3 mOl11hs after tliefracture was sta hilized \Vith t\Vo lag screws (4.5 cortex screws).

Wound Closure The deep brachial fascia, subcutaneous tissue and skin are closed in layers. Post-operative Care As for Operati ve Technique 15.8.

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Intercondylar fractures

Positioning Dorsal recumbency with the affected leg pulled cranially. Assistant Essential.

Tray Extras Appropriate sized plate and screw set, drill bits, etc.; K-wires; tension-band wire; pin/wire cutters; pliers/wire twisters; drill; Gelpi and Hohmann retractors; self-locking bone holding forceps; pointed reduction fo rceps; Vulsellum forceps; hacksaw or gigli wire. Surgical Approach A skin incision is made over the caudolateral aspect of the elbow; the subcutaneous fat and fascia are incised and undennined to allow reflection of skin from both sides of the elbow. Fascia along the cranial border ofthe medial head of the triceps are incised and the ulnar nerve is identified and retracted from the olecranon (Figure 15.30a). The crarual margin of the lateral head of the triceps is also freed from its fascial attachments. The proximal shaft of the u~la is exposed by separating the flexor carpi ulnaris and extensor carpi ulnaris muscles.

Extensor carpi ulnaris m. Pre-placed

wire

Flexi carpi ulnaris m.

~~~

Fascial inciSion to reveal ulna n.

Anconeus m.

Olecranon and Triceps ] m. reflected

Osteotomy of Olecranon

Figure J5.30: Transo{ecralloll approach/or reduction and fixatiol1 of imercol1dylar fractures .

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Intercondylar fractures

A hole is drilled tranversely through the ulna with a 2 mm drill just distal to the elbow; a length of orthopaedic wire (18 or 20 gauge) is passed through the hole, and fashioned into a loop. This wire will be used later as a tension band but at this stage it makes a usefu l handle for an assistant to exert traction on the ulna during exposure and reduction of the humeral condyles (Figure 15.30a). If a screw is to be used to repai r theolecranon osteotomy, the screw hole should be prepared and tapped prior to osteotomy. Transverse osteotomy of the olecranon is performed with a saw or gigli wire distal to the tendon of insertion of the triceps on the olecranon and proximal to the anconeal process. Protect the ulnar nerve during this procedure. The olecranon is reflected dorsally with the attached triceps muscle mass; remnants of the anconeus and joint capsule are refected from the caudal aspect of the e lbow to complete exposure of the condyles (Figure 15.30b). Rel/uctiOIl and Fixation The condyles are reduced, ensuring accurate reconstruction of the articular surface. The assistant exerts traction on the ulnar wire to steady the elbow. The medial condylar fragment is held wit h small bone holding forceps while the lateral condyle is aligned in its normal position with the medial condy le and held in reduction with pointed reduction forceps. The proximal ends of the condylar fragments are transfi xed with a K-wire (Figure 15.3 Ib). In fracture types I and II, a lag screw can be used instead, if the fragm ents are large enough. Once this area has been stabilized, the articular margins of the fracture can be checked again and final adj ustments in reduction made before inserting a transcondylar lag screw from lateral to medial (see lateral condylar fracture repair) (Figure 15.3 1c). Initial fixation of condyles with a Kirschner wire

Transcondylar lag screw

Condyles fixed to shaft with Kirschner wire or lag screw

Application of DCP plate

Lateral condyle

Fig ure 15.31: (a) -(e) Reductioll andfixatioll of a 'Y' jractu re using K-\Vire~.., transcondylar lag screw alld plate applied to medial supracol1dylar ridge of the humerus. (f) 771ree-montll follow-up cralliocaudal radiograph of a Sprillger Spaniel that fwd a 'Y'jracture. Fixation/wd been achieved usil1g a lrallscolldylar lag screw (4.5 cOr/ex screw), supracondylar lag screw (2. 7 c~r/ex) alld a plate (8-llOle 3.5 DC?) applied to medial supracol1dylar ridge.

The distal shaft of the humerus is grasped with self- locking bone holding forceps while the condyles are grasped with pointed reduction forceps. Reduction of the supracondylar portion of the fracture is then achieved by a combination of direct traction and toggling the fracture surfaces against each other. If possible, the condyles are temporarily attached to the shaft at this stage with a K-wire placed obliquely across the supracondylar fracture line (Figure 15.3 1d). A plate (3.5 or 2.7 DCP) is then applied to the caudal aspect of the medial supracondylar ridge. This is a flat surface and the plate should require little or no contouring (Figure 15.31e,f). If a K-w ire is not used: having ensured that it is possible to reduce the supracondylar fracture site, disengage the fragments and rotate the medial condyle latera ll y so that the medial supracondy lar ridge is easily visible. Attach the dista l end of the plate to the caudal aspect of the medial condylar ridge. It is usually possible to place three screws, especially if a 2.7 DCP is used for fixation , but take care that the most distal screws do not penetrate

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the articular surface. Having attached the plate, the free prox imal end of the plate can be used as a lever arm to complete reduction of the fracture site: hold the plate against the bone with self-locking bone holding forceps while the first two screws are inserted proximal to the fracture site. Once stability is achieved, the forceps can be removed and the rest of the screws placed. In large dogs a second, smaller plate can be applied to the lateral supracondylar ridge to improve stability (Figure 15 .32). In youn g puppies, pins or K-wires can be used to attach the condyles to the shaft, but plate fixation gives the best results.

Figure J5.32: Post-operative crolliocouJaf radiograph oj a 4-year-old German Shepherd Dog with a "T'jracfllre. The jracflIre has been stabilized with a IrclIlscolldylar lag screw (4.5 11/111 cortex screw) and two plates all the supracondylar ridges (6-/lOle 2.7 DCP medially, 4-//O/e 2.7 DCP /a{erally).

Wound Closllre The olecranon osteotomy is repaired with a lag screw (Figure 15.33) or two K-wires are used in combination with the pre-placed ulna wire which is used as a tension band. The lag screw is preferred as it causes less soft tissue interference and can usually be left in situ. The K-wires, by contrast, may loosen - causing local soft tissue problems - and will require remo val. The olecranon is reduced and the lag screw is inserted down the long axis of the olecranon, using the prepared drill hole. The screw is not full y tightened at this stage. The proximal end of the ulna wire loop is cut off; the two ends of the wire are crossed in a figure-of-eight and brought over the caudal edge of the olecranon. One end of the Fig ure 15.33: Lateral view of Figure J5.32 wire is passed through the insertion of the triceps, keeping close to showing a 4 1/1111 cancel/oils screw + the bone and taking care to ensure that the wire wi ll be anchored tellsiOIl -bolld wire Ilsed for repair of the under the screw head. The wire is then brought down to one side of olecranon osteotomy. the olecranon, where it is twisted tight with the other free end of wire to complete the proximal loop of the tension band. (Because the wire tension band is bridging such a short osteotomy, it is possible to get good tension by placing twists in one side only rather than placing twists on either side of the olecranon.) Afterthe tension band has been completed, the lag screw is tightened. The triceps fascia is repaired on both latera l and medial sides (avoid the ulnar nerve in sutures on the medial side). The rest of the wound closure is routine.

Post-operative Care A Robert Jones bandage is app lied for 5 days post-operati vely to provide support and to control post-operati ve swelling; otherwise management is as descri bed for lateral condylar fractures. Implants are generally left ill situ unless loosening causes soft tissue problems. The proximal ends of K-wires used. for repair of olecranon osteotomy are the most common problem but once these wires have been removed any associated lameness tends to resolve.

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CHAPTER SIXTEEN

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Radius and Ulna Warrick 1. Bruce

INTRODUCTION Fractures of the radius and ulna constitute 8.5% to 17.3 % of all fractures seen in the dog and cat (SumnerSmith and Cawley, 1970; Phillips, 1979). They result from many types of trauma, including road traffic accidents, gunshot accidents, falls from heights, kicks, bites and crushing injuries. In some small breeds, they can be seen following minimal trauma. Pathological fractures secondary to neoplasia or metabolic bone disease may also occur.

Fractures of the radius and ulna are associated with a relatively high incidence of complications (Vaughan, 1964; DeAngelis et aI, 1973). These include delayed union, non-union, malunion, osteomyelitis, and angulardeformities due to growth plate damage. The radius and ulna account for around half of all cases of long bone fracture non-union recorded in the dog (Vaughan, 1964; Sumner-Smith and Cawley, 1970; Atilola and Sumner-Smith, 1984). Toy and miniature breeds have a disproportionately high incidence of delayed and non-unions (Sumner-Smith, 1974). Problems are also encountered in large and giant breeds of dog due to the large forces placed on fractures and fixation devices in the antebrachium. '

Lateral view

Figure 16.1: Simple/rae/ure through the semi-ilillar notch of

the ulnG.

PROXIMAL ULNA All fractures in this area require open reduction and internal fixation to counteract the powerful traction

of the triceps group of muscles. These forces are equalized by use of the tension -band principle (Chapter 9).

Simple fractures through the semi-lunar notch See Figure 16.1 and Operative Technique 16.1.

Avulsion fracture of the olecranon See Figure 16.2 and Operative Technique 16.1.

Comminuted fracture of the proximal ulna with fracture of the anconeal process See Figure 16.3 and Operative Technique 16.2.

Lateral view Figure 16.2: A vllisioll/racture of the olecranon.

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Manual of Small Animal Fracture Repair and Management the radial head occurs as a result of tearing of the annular ligaments and contracture of the biceps brachii and brachialis muscles. In some cases separation of the radius and ulnar diaphysis occurs secondary to rupture of the interosseous ligament.

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In recent injuries, where the interosseus ligament

remains intact, a closed reduction and closed nonnograde insertion of a pin in the ulna may be attempted. However, this is frequently difficult to achieve and open reduction with internal fixation is required (see Operati ve Tecllnique 16.3).

PROXIMAL RADIUS

Figure /6.3: Comminutedfractllre o/the proximal ullia.

Fractures of the ulna with concurrent dislocation of the radial head Fracture of the proximal third of the ulnaand anterior dislocation of the proximal epiphysis of the radius (Figure 16.4) was first described in humans by Monteggia (1814). A spectrum of injuries (Monteggia lesion) can result in dislocation of the elbow joint and fracture of the ulna and these ha ve been classified on the basis of direction of the dislocation and the angulation of the ulnar fracture (Bado, 1962; Schwarz and Schrader, 1984).

These fractures are uncommon as the wea ker lateral humeral condyle often fractures first, thus sparing the proximal radius. When they do occur, they are often articular and can be associated with fra ctures of the ulna and dislocation of the elbow joint.

Salter-Harris Type I fracture Fractures throug h thi s me taph yseal grow th plate (Figure 16.5) require open reduction if there is significant fracture displacement and reduction cannot be accomplished by closed means (Operative Technique 16.4).

Luxated radial head

Torn annular ligament

Figure 16.5: Salter- Ha rris Type J fraclure a/the proximal radius.

Articular fractures Interosseous ligament Lateral view

Figure 16.4: Type I Monteggiajracfure.

All fracture-dislocations of tilis nature are rare, but cranial dislocation of the radial head, with cranial angulation of the fractured ulna (type I Monteggia lesion) was found to be the most common in dogs and cats (Schwarz and Schrader, 1984). It has been proposed that this injury is caused by a direct blow to the olecranon when the antebrachium is extended and weightbearing (Wadsworth, 198 1). Displacement of

These generally require accurate anatomical reduction and fi xation with lag screws and K -wires, depending on the size of the fracture fragments (Operati ve Technique 16.4).

Comminuted fractures of the proximal radius Comminuted fractures in this area are difficult to manage and require a wide dissection (Bloomberg, 1983). Salvage procedures such as ostectomy of the radial head (prymak and Bennett, 1986) and elbow joint arthrodesis have been advocated for non-reconstructable fractures of the radial head (Bloomberg, 1983).

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Radius and Ulna The prognosis depends on the type of fracture and the accuracy of reconstruction. Metaphyseal growth plate fractures heal quickly and carry the best prognosis. However, premature closure of the growth plate and short radius syndrome is a potential complication. Elbow joint osteoarthritis is a common sequel to fractures of the proximal radius.

RADIAL AND ULNAR DIAPHYSES These fractures most commonly affect the middle and distal third and frequently involve both bones. Isolated fractures affec ting the shafts of either bone are less common (Philli ps, 1979; Ness and Armstrong, 1995). Table 16.1 suggests appropriate treatments.

Procedure

Comments

Casts or splints

Treatments with casts or splints should be reserved for closed fractures involving only one bone, incomplete fractures, or minimally displaced transverse, spiral or oblique fractures that are relatively stable.

Bone plating Operati ve Technique 16.5

Plate fixation can be used for most radial diaphyseal fractures in dogs and cats. It is the preferred method of treatment fo r non-unions, delayed unions and distal fractures in miniature and toy breeds of dogs.

External fixation The external fi xator is appropriate for the repair of Operati ve nearly all diaphyseal Technique 16.6 fractures of the radius and ulna. It is particularl y suitable fo r the treatment of severely comminuted fractures and open fractures with soft tissue loss. Intramedullary pinning

This method of fi xation is not recommended for fractures of the radius.

Table 16,1: Decisiol1 makil1g ill the management o/radial alld uinar diaphyseal fra ctures.

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E xtern a l support Many fractures of the radius and ulna of the dog and cat are amenable to treatment with casts or splints if adequate closed reduction can be attained and maintained. The surgeon should aim for at least 25 %end-toend fracture segment contact with no angulation (Lappin er al., 1982). In some cases a limited open approach may be required to align the fragments adequately. Best results are achieved in youn g (less than 1 year) medi um-sized dogs (Lappin er al., 1983) . WARNING Casts and splints should not be used as the sale means of support in giant breeds, nor should they be used for distal fractures of the radius a nd ulna in miniature and toy breeds of dogs. Care must be taken in small dogs and cats as fracture alignment is often difficult due to small bone diameter, poor soft tissue support, and tension in the carpal and di gital flexor muscles which tend to displace the frag ments. In addition there are technical difficulties in applying lightweight casts of suitable strength that do not slip distally in these animals (Chapter 7). Bone plating Bone plating is a popular method of fi xation for fractures of the radius and ulna. The natural flattening and cranial curvature of the radius make its dorsal (tension) surface ideal for plate application. Both compression and neutrali zation plates have been used with success (Lappin er aI. , 1983). In most dogs and cats only the radius is plated and fi xation of the ulna is unnecessary. Platin g both the radius and ulna is recommended in large and giant breeds of dog because of their large size and the extreme forces placed on the fixation devices (Lappin er al., 1983; Brinker er aI., 1990). External fixation The extern al fi xator can be applied following closed or limited open reduction. It may be used alone or as an adjunct to some form of internal fixation such as lag screws or cerclage wires. All configurations (unilateral, bilateral, biplanar) have been used successfull y in the antebrachium. The unilateral uniplanar design is the simplestto apply, has the lowest complication rate and is adequate fo r the majority of cases. Intramedulla ry pinning Intramedullary pinning of the radius is not recommended due to the high complication- rates associated with this technique (Lappin er aI., 1983). The radius is less amenable to pinning compared with the ulna and other long bones as it has a relatively straight oval-shaped medullary canal which is bounded by articular carti lage at both ends.

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This means that both the elbow and the antebrachiocarpal joints are endangered when pinning and only small diameter pins may be used. An intramedullary pin poorly

resists rotational instability and axial compression and potentially damages the endosteal vessels to a bone with a tenuous distal blood supply. There are bettermetilOdsof radial fracture fi xation available.

Fractures of the distal third of the radius and ulnar diaphyses in miniature and toy breeds These fractu res are associated with a disproportionately high incidence of delayed and non-unions (SulllilerSmith, 1974). The main reason for this phenomenon is thought to be inadequate immobilization, but factors such as infection, delays in fracture stabilization and the tenuous blood supply to the bones may also be contributory (Sumner-Smith and Cawley, 1970; Hunt ef ai., 1980; Bartels, 1987; Eger, 1990). Rigid stabilization is mandatory and plating with mini plates or mini T-plates is recOlllinended (Figure 16.6). Bone plate removal is also recommended as a number of cases have been observed where the radius has refractured at the proximal end of tile plate several years later as a result of local loss of bone strength. It is the author's policy to remove these plates between 6 months and I year post-operatively. Earlier plate removal and cancellous bone grafting has been recommended (Lesser, 1986). The limb must be supported in a Robert Jones bandage for I to 2 weeks following plate removal and the dog 's activity restricted for 4 weeks.

bonded together on either side of the limb. Staged disassembly may be performed from 9 to 12 weeks post-operatively.

DISTAL RADIUS AND ULNA Fractures of the distal radius and u~la are common and frequently occur following fa lls from heights. Open fractures tend to occur in this area as there is little soft

tissue protection. Many fixation methods have been used to repairdistal antebrachial fractures, including extemal coaptation alone or in combination with lag screws, crossed K-wires or pins and cerclage wire (Gambardella and Griffiths, 1984), internal fixation with Rush pins, T-plates, hook plates (Bellah, 1987) and extemal fixation. The ultimate choice of fixation techrtique depends on the size of the bone, the nature of the fracture, the facilities available and the financial resources of the owner.

Salter-Harris Type I fractures Fractures of the distal radial and ulna metaphyseal

growth plates are common in the immature animal and can result in premature closure of these growth plates (Chapter II). Fracture through the distal radial growth plate is usually accompanied by fracture of the distal ulna or its growth plate (Figure 16.8). Early closed reduction should be attempted and stable fractures can

An effective and economica l alternative to bone plating is to use transfixation pins and acrylic cement (F igure 16.7) (Eger, 1990; Tomlinson and Constantinescu, 1991). To ensure accurate reduction, a limited open approach is recommended. K-wires are driven transversely through the radius above and below the fracture and the exposed ends of the wires are

Figure 16.8: Salter- Harris Type l/racture a/the distal radius lVith concurrellt fracture 0/ the distalllilla.

Figure 16.6: Distal amebrachialjractllre ill a 1.2kg Chihuahua repaired with a 5 hole 2 mm plate 011 the cranial radius.

Figure 16. 7: Distal antebrachial fracture in a 4.5kg Poodle repaired with a bilateral external jixator comprising /1l111l01lthreaded pillS alld methylmethacrylate connecting bars.

be managed with external coaptation for three weeks. Less stable or irreducible fractures require open reducti on and the fracture should be stabilized us ing cross or parallel pinning teclmiques (Operative Technique 16.7).

Styloid fractures Avulsion fractures of the radial or ulnar styloid processes give rise to instability of the antebraclliocarpal

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Radius and Ulna

Collateral ligaments '-----1/~..--,./

Figure 16.9: A vulsioll fracture ofradiaL styloid process with resu ltalll instability of the alllebrachiocarpal j oint.

joint as the collateral ligaments originate on the styloid processes (Figure 16.9). These fractures may occur in association with subluxation or luxation of this joint and should be accurately repaired by internal fixation (Operati ve Technique 16.8).

Articular fractures Articular fractures require perfect anatomical reduction to minimi ze secondary osteoarthritis. The articular surface is repaired with lag screws or K-wires, depending on the size of the fragment(s). In commi nuted fractures the distal fragm ents are then aligned and reattached to the radial metaphysis by means of a bone plate. Hook and T-plates are most useful in this location. A cranial approach is used as described in Operative Technique 16.7.

REFERENCES AND FURTHER READING Atilola MAO and Sumner-Smith G ( 1984) Non-uni on fractures in dogs. JOllmal of Veterinary Orthopaedics 3, 2 1. Bado JL (1962) The Monteggia Lesion. CC Thomas, Springfield. Bartels KE (1987) Non-uni on . Veterinary Clinics of North America 17, 799. Bellah JR ( 1987) Use of a double hook plate for treatment of a distal radial fracture in a dog . Velerinary Surgery 16, 278.

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Bloomberg MS (1983) Fractures of the radius and ulna. In: Currem Techniques ill SlIIall AI/ima! Surgery, 2nd edn, cd. MJ Boj rab. Lea and Febiger, Philadelphia. Brinker WO, Piermaltei DL and Fl o GL (1990) Fractures of the radius and ulna. In: Handbook oj Small Animal OrlllOpaedics alld Fra cture Trealmellf, 2nd edn . WB Saunders, Philadel phia. DeAngelis MP, Olds RB, Stoll SG et 01. (1973) Repair of fractures of the rad ius and ulna in small dogs. Journal oJthe American Animal Hospital Associatioll 19,436. Denny HR ( 1990) Pectoral limb fractures. In : Canine Orthopaedics, 2nd edn, ed. WG Whinick. Lea and Febiger, Philadelphia. Eger CE (1990) A techniquc for the management of radial and ulnar fractures in miniature dogs using transfixation pins. JOllrnal of Small Animal Practice 31, 377. Egger EL (1990) External skeletal fi xation. In: Cu rrellt Techlliques ill Smal/ Animal Surgery, 3rd edn, cd. MJ Bojrab, SJ Bri chard and JL Tomlinson Jr. Lea and Febiger, Philadclphi a. Gambardella PC and Griffiths RC (1984) A technique for repair of oblique fractures of the distal radius in dogs. Journal of the American Animal Hospital Associmioll 20, 429. HuntJM, Aitken ML, Denny HR andGibbsC( 1980) Thecom plications of diaphyseal fractures in dogs: a review of 100 cases. Journal oj Smal/ Allillla! PraClice 21 , 103. Lappin MR,Aron ON, Herron HL and Malnati G ( 1983) Fractures of the radius and ulna in the dog. Journal oj the Alllericall AI/imal Hospital Association 19, 643. Lesser AS (1986) Cancellous bone graft ing at plate relllovalto counteract stress protection. Journal oJtlle Alllericall Veterinary Medical Associatioll 189, 696. Marti JM and Miller A ( 1994) Delimitation of safe corridors fo r the insertion of external fixator pins in the dog. 2: Forelimb. Journal oj Small Anima! Practice 35, 78. Miller A (1994)Thecarpus. In: Manllal of Small Animal Arthrology,ed. JEF Hou lton and RW Coll inson, pp. 211-233. British Small Animal Veterinary Association, Cheltcnham, Gloucestershire. Monteggia GB (18 14) Illstituzioni Chirurgiche, 2nd cdn. G. Maspcr, Milan. Ness MG and An1lStrong NJ ( 1995) Isolated fracture of the radial diaphysis in dogs. Journal oj Sma/l Allimal Practice 36, 252 . Phillips IR (1979) A survey of bone fractu re in the dog and cat. JOl/mal oj Small AI/ima! Practice 20, 661 . Picnnattei, DL (1993) An Arias oJSlIrgical Approaches to the Balles and Joillls oJthe Dog and Cm, 3rd edn . WB Saunders, Philadelphia. Prymak C and Bennen D (1986) Excision arthroplasty of the humcroradial joint. JOllrnal oj Small Allima! Practice 27, 307. Schwarz PO and Schrader SC (1984) Ulnar fractu re and dislocation of the proximal radial epiphysis (Monteggia lesion) in the dog and cat: a review of28 cases. Journal oJthe Americall Veterinary Medical Associatioll 184, 190. Sumner-Smith G (1 974) A comparative in vestigation into the heali ng of fra ctures in miniature Poodles and mongrel dogs. Journal ofSmall Animal Practice 15, 323. Sumner-Smith G and Cawley AJ (1970) Non -union fractures in Ihedog. Journal oj Small Anima! Practice 11, 3 11. Tomlinson JL and Constantinescu GM (199 1) Acrylic external skeletal fi xation of fractures. Comilluillg Education Article No.6, 13,2, 235. Vaughan LC ( 1964) A cl inical study of nOll-union frac tures in the dog. Journal oJSmall Animal Practice 5, 173. Wadsworth P ( 1981 ) Bi omechanics of the luxation of joints. In: Pathophysiology in Small Animal Surgery, ed. MJ Bojrab. Lea and Febiger, Philadelphia .

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Fractures through the semi-lunar notch and avulsion fractures of the olecranon

Positioning Dorsal rec umbency with the affected limb extended craniall y (Figure 16.10). Assistant Ideall y.

Tray Extras K-wires; chuck; air or electric drill and bits; pin/w ire cutters; pliers; Kern bone holding forceps (or po inted reduction fo rceps); periosteal elevator; ± appropriate bo ne plating and screw set; ± ASIF 2.0 mm parallel drill guide. Surgical Approach Making a caudomedial incIs Ion over the olecranon has several advantages: it allows for identificati on of the ulnar nerve; the skin is thinner in this area and therefore heals with less scarrin g; and th e incision is hidden from view. The s kin is reflected laterall y and the underlying flexor carpi ulnaris, anconeus and ulnaris lateralis muscles are elevated from the ulna (Figure 16. 10).

Flexor carpi uJnaris m.

Ulnar n.

Superficial digital flexor m.

Fig ure 16. 10: Caudal exposure of the proximal tllna.

Reductioll lllld Fixatioll The proximal ulna is held with Kern bone holding forceps and the first pin is dri ven in a retrograde fashion from the fracture surface to emerge at the point of the elbow (Figure 16.11a). The pin is then backed out until its ti p is level with the fracture surface. With the patient's elbow held in extension, the fracture is accurately reduced and the pin is driven in a norrnograde direction to anchor in the cranial con ex of the ulna (Figure 16. 11b). A second, more caudal pin may be placed parallel to the fi rst using a parallel drill guide (Figure 16.1 Ic).

(a)

(b)

(e)

(d)

Figure 16.11: Repair proximal ulnar

0/0

jracflire usillg pillS alld

a tellsion balld wire (see teXT for details).

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Fractures through the semi-lunar notch and avulsion fractures of the olecranon

PRACTICAL TIPS It is easiest to power-drive small diameter arthrodesis or K-wires using an air or electric drill.

Larger Steinmann pins may be placed by hand, using a Jacobs chuck. When placing larger diameter pins by hand it is often easier, and more precise, to pre-drill a pilot hole using a smaller diameter drill bit. A hole is then drilled transversely through the ulna 1 to 2 em distal to the fracture. A length of stainless steel wire is passed through the hole and its free ends are crossed. Similarly, a length of wire is passed around the caudal aspect of the olecranon cranial to the pins. The ends of the two wires are then twisted together alternately until the tension band is tight. WARNING The proximal loop of the tension-band wire must pass as close as possible to the bone to avoid pressure necrosis at the triceps tendon insertion. Finally, the pins are bent in a caudal direction close to the end of the olecranon and are cut, leaving a small hook. Each pin is twisted 180 0 cranially so that the bent end of the cranial pin lies over the tension-band wire (Figure 16. lld). The diameter of the pins is based on the size of the animal and the ability to place two pins parallel to each other in the ulna. In small dogs and cats, a single pin placed within the intramedullary canal and a wire tensionband is often sufficient. However, if this technique is used, the fracture should be oblique and interlocking to prevent rotational instability, and the pin should extend the length of the proximal third of the ulnar diaphysis. Stainless steel wire of 0.8 mm diameter is sufficient in cats and toy dogs; larger dogs require wire of 1- 1.2 mm diameter. WARNING Note the lateral curvature and narrow intramedullary canal of the proximal ulna. Care must be taken to avoid exit ing through the side of the ulna or entering the elbow joint when driving pins in this area. Care must be taken to identify and protect the branch of the ulnar nerve that courses near the medial humero-ulnar articulation.

Wound Closure Routine. Periosteum and deep fascia can be closed as one layer. Post-operative Care A light dressing is applied for a few days and passive elbow flexion/extension exercises should be encouraged post-operati vely. Exercise should be controlled for 4 to 6 weeks. On occasions the pins may loosen, or their protruding ends may cause soft tissue irritation; this would necessitate removal once fracture healing is complete. • Alternative Technique In medium-sized to large breeds of dogs, place the fragments under compression using a lagged cortical or cancellous screw in combination with a pin and tension-band wire (see Figure 15.33).

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OPERATIVE TECHNIQUE 16.2 VetBooks.ir

Comminuted fractures of the proximal ulna and fractures of the anconeal process

Positioning Dorsal recumbancy with the affected limb extended craniall y. The contra lateral limb is pulled caudall y and secured. Assistant Idea ll y.

Tray Ext,.as Air or electric drill and bits; Kern bone holding forceps; pointed reduction forceps; periosteal elevator; West or Gelpi self retaining retractors; Hohmann retractor; semitubular plate or DCP (3.5 for large and mediumsized dogs, 2.7 for small breeds, 4.5 for giant breeds); appropriate bone plating and screw set; plate benders.

Approach A caudomedial approach to the ulna is made (see Operative Technique 16.1). The incision may need to be extended distall y to allow plate application to the ulnar diaphysis. Reduction mul Fixation The anconeal process should first be reduced and fixed to the olecranon in cases complicated by its fracture. A screw is placed in a lagged fashion, either from the caudal aspect ofthe olecranon into the anconeal process, or by countersinking an intra-articular screw cauda l to the articular surface of the anconeal process. Alternatively it may be excised if it cannot be lag screwed back (Denn y, 1990).

A DCP or semi tubular plate may be applied to the caudal aspect, or tension-band surface of the ulna. In this position, the plate acts as a tension band and resists the pull of the triceps muscle. In cases where acc urate anatomical reduction is impossible, the plate acts as a buttress preventing fracture collapse. Bone plates can be applied to the caudolateral surface in cases where the width of the ulna is too small to accollUnodate bone screws. A bone plate is then contoured and applied to the proximal fragment first. At least two bone screws should be placed in the proximal fragm ent (see Figure 16.14). Where there is a small proximal fragment, the plate is contoured around the point of the elbow. In giant breeds a hook plate may be useful. The fracture is reduced with the elbow joint extended and bone holding forceps are used to fi x the plate to the distal fragment prior to screw placement. Smaller fragments are held in position with lag screws or small K-wires.

Accurate anatomical reduction of any articular components is essential to minimize secondary osteoarthritis. WARNING Care must be taken to avoid placing screws through the articular surface of the semiluna,' notch.

WOllnd Clos",.e Routine. Periosteum and deep fascia can be closed as one layer. Post-operative Ca,.e A Robert Jones bandage is used for a few days to limit swelling. Early use ofthe elbow should be encouraged with passive range of motion exercises and controlled walking. If fixation is tenuous or bony defects remain at the fracture site then it is safest to maintain elbow motion without weight bearin g by using a carpal flex ion bandage.

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OPERATIVE TECHNIQUE 16.3 VetBooks.ir

Fractures of the ulna with concurrent dislocation of the radial head (Monteggia lesion)

Positioning The patient is positioned in dorsal recumbency with the affected limb extended cranially.

Assistant Ideally. Tray Extras Periosteal elevator, pointed reduction forceps, Gelpi self-retaining retractors, Hohmann retractors; chuck; K-wires, pliers, pin cutters, ± drill, ± appropriate plate and screw set, drill bits etc.

Surgical Approach A combination of a lateral approach to the elbow joint (see Operative Technique 16.4) and caudal approach to the ulna (see Operative Technique 16. I) is made to expose the fracture-dislocation. Reduction and Fixation The radial head is reduced by sliding it medially over the lateral humeral condyle with the elbow held in flexion. Reduction of the radial head is frequently complicated by the interposition of soft tissues, bone fragments, or an organized blood clot. Reduction is maintained using pointed reduction forceps (Figure 16.12). Where possible, the torn annular ligaments are sutured with polydiaxanone. In adult animals, the author prefers to fix the radial head securely to the ulna using a bone screw (medium to large size dogs) (see Figure 16.13a) or small pin (small dogs and cats) (see Figure 16.13b). An alternative means of fixation is to use a full or hemicerclage wire to maintain anatomical reduction of the radius. The ulna may be stabilized by a number of methods depending on the location and type of pin; more proximal fractures require pin and tension-band wire fixation (see Figure 16.13b). Comminuted fractures usually require bone plate fixation (see Figure 16.14).

Section A-A Radius

Ulna

Reduction forceps

Figure 16.12: Managing Monteggia/ractures. Once reduced, the radial head call be temporarily held in position using pointed

reductioll forceps. The cross-section shows the position of a transfixing screw to maintain the reduction during healing.

WARNING Neurological injuries are commonly associated with this type of fracture in man and have been reported in dogs (Schwarz and Schrader, 1984). WARNING Transfixing the radial head to the ulna in an immature animal may interfere with the independent growth or the radius and ulna and result in elbow joint incongruity and angular limb deformities.

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OPERATIVE TECHNIQUE 16.3 (CONTINUED) VetBooks.ir

Fractures of the ulna with concurrent dislocation of the radial head (Monteggia lesion)

Figure 16.14: Repair of a Type I MOllleggia fracture ill a 35 kg DeerllOulld. The radius has been secured to the ui lla using transfixion screws (most

proximal). The commit/Illed ui llor shaft /racfIl r e has been

partially reconstru cted lVith lag screws and buttressed with a cauda/ateral plate.

16.13: (a) Repair of a Type I MOflfeggia fracture ill a 16 kg Border Collie llsing a trallsfixillg screw to maimain reduction of the radial head. The oblique fracture a/The ulllar diaphysis was repaired with a lag screw. (b) Repair of a Type I MOllfeggia!racture ill a cat. The radius lias been secured to the uilla llsing a K-wire alld fhe /l/Ilo r shaft has been repaired using all

i1l1ramedullary pill alld a tellsion band wire wirh two additional cerclage wires.

Wound closure Routine. Periosteum and deep fasia can be closed as one layer. Post-operative care The limb should be supported in a padded dressing or cast in slight fl exion for 2 to 3 weeks post-operati vely. Transfixing screws and pins should be removed 3 to 4 weeks post-operati vely. Prognosis Guarded due to the high incidence of post-operati ve complications, such as non-union of ulna, reluxation of radial head, traumatic periarticular ossification, osteoarthritis, reduced elbow joint range in motion, nerve damage, osteomyelitis, implant migration and synostosis (Schwarz and Schrader, 1984). The prognosis is better in cases where the interosseus attachments of the radius to the ulna are preserved.

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OPERATIVE TECHNIQUE 16.4 VetBooks.ir

Fractures ofthe proximal radius

Positioning Dorsal recumbency with the affected limb extended caudally. The contralateral limb is pulled caudally and secured (Figure 16.15).

Figure 16.15: Repair a/proximaL radial fractures: patient positioning.

Assistant Ideally. Tray Extras Periosteal elevator; pointed reduction forceps; Hohmallllll retractor; Gelpi self-retaining retractors; chuck; pin/wire cuners; pliers; wire benders; ± air or electric drill and bits; K -wires; ± appropriate bone plating and screw set.

Approach A lateral approach to the elbow joint is used to expose the radial head (Figure 16.16). The origin of the common digital extensor muscle may be incised and retracted and the supinator muscle may be elevated off the radius for bener exposure. For articular fractures, the origins of the three extensor muscles may be included in an osteotomy of the lateral humeral condyle (piermattei, 1993). Transection of the annular and collateral ligaments may also be necessary to gain adequate exposure.

Lateral humeral epicondyle Supinator m. Radial nerve

Radial head

Extensor carpi radialis --H'Hf-

Cormninuted fractures require a wide dissection and a bilateral approach to the elbow joint can be used. Gelpi retractors

Figure 16.16: Repair a/proximal radial fractures: lateral exposure a/the proximal radius.

Reduction and Fixation Fractures in this area are reduced with the elbow flexed. Metaphyseal growth plate fractures are stabili zed with a K-wire driven from the proximolateral surface of the radial head near the articular surface, across the fracture, to anchor in the medial cortex of the radius. A second K-wire inserted in a similar direction or from the medial side may further improve stability (Figure 16.17).

Figure 16.17: Repair o/a SaiterHarris Type I fracture a/the proximal radius Ilsing crossed K-wires.

'it""'o;I;L-Growth plate

1i'~±:"Kirschner wires

Cranial view

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Fractures of the proximal radius

Si mple articular fractures are repaired with lag screws and K-wires. For more complex fractures, the articular surface is repaired first with lag screws and then aligned and reattached to the radi al metaphysis by means of a bone plate . Small non-reducible articular fragm ents, which would otherwise cause mechanical irritation to the joint, should be removed. WARNING The radial nerve lies deep to the supinator muscle and must be protected during surgery.

Wound Closure Routineseparate layer closure. Transected portions of the collateral liga ment are s utured with polydioxanone. Transected extensor muscles areslltured with a hori zontal mattress or cniciatesliture pattern . A n osteotom ized

lateral humeral epicondyle is reattached wit h a lag screw or pins and tension-band wire.

Post-operative Care Proximal radial growth plate fractures requiresupport in a Robert Jones bandage for I to 2 weeks and exercise is restricted for 3 t04 weeks. Hea ling is usuall y rapid and K-wiresare removed from 4 weeks post-operatively. Artic ular and more complicated fract ures may require support in a Robert Jones bandage or cast for 2 to 6 weeks depending on the rigidity of fixation and the speed of healing.

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OPERATIVE TECHNIQUE 16.5 VetBooks.ir

Bone plating diaphyseal fractures of the radius

Positioning Dorsal recumbency with the limb pulled either caudally (see Figure 16.5) or cranially depending on the approach. The contralateral limb is pulled caudally and secured.

PRACTICAL TIPS Use a beanbag to support the patient rather than a high-sided plastic cradle as a beanbag is more compliant and tends to be less intrusive. Hanging the animal frolll the affected limb whilst preparing for surgery fatigues the muscles and aids ill fracture reduction. Assistant Ideall y.

Tray Extras Periosteal elevator; Hohmarmn retractor; Gelpi self-retaining retractors; pointed reduction forceps (or bone holding forceps of choice); bone cutters; plate benders; air or electric drill and bits; appropriate bone plating and screw set.

Approach The craniomedial approach is classically used to expose the diaphysis of the radius (Figure 16.18). For fractures of the proximal to middle radial diaphysis, a lateral approach between the extensor carpi radialis muscle and the common digital extensor muscle is preferred (Figure 16.19) (piermattei, 1993). The diaphysis of the ulna is exposed by a caudal approach. Pronator

teres m. Flexor carpi radialis m.

Extensor carpi

radialis m.

Superficial

digital flexor m.

Shaft of radius ,,-;--

-I./..L

Extensor

carpi radialis m.

Ill-- - r

Common

digital

extensor m.

.\.\---/-- - Lateral digital

extensor m. Abductor

policis longus m. Gelpi retractors

Figure 16.18: ,Craniomediai exposure a/the radial diaphysis. Fig ure 16.19: CranioiareraL exposu re of the radial diaphysis .

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OPERATIVE TECHNIQUE 16.5 (CONTINUED) VetBooks.ir

Bone plating diaphyseal fractures of the radius

RetiuctiOIl allti Fixatioll Fracture reduction may be accomplished by bending the limb caudally at the fracture sitc, toggling the bone ends against each other and then straightening the limb. Where there is significant overriding of the fracture a Hohmannn retractor may be used to lever the distal fragment into alignment. Sometimes the radius cannot be reduced without first reducing the ulna. In these cases, it is useful to cut back the ulnar fragment.

PRACTICAL TIP Beware of soft tissue intel·position at the ulnar fracture site preventing accurate I·adial fracture alignment. When a plate is applied to the cranial surface of the radius (see Figure 16.20), it should first be prestressed to allow for the natural cranial curvature of the radius and to ensure compression at the transconex (see Chapter 9). It is best to apply the plate to the distal radial fragment first so that it may be used as a lever to aid in reduction. Once the fracture is reduced, bone holding forceps are used to fix the plate to the proximal fragm ent prior to screw placement. Oblique fractures are stabili zed with pointed reduction forceps, and where possible a lag screw, or alternati vely a K-wire, is placed across the fractnre. TIllS will prevent the fragments from slipping past each other during plate application.

Figure 16.20: (a) Obliquejracture o/the radial shaft with a commilillfed ulnar fracture. (b) Tltejraclured radills was repaired /Ising an illlerjragmelltary lag screlV and a craniaL nelltralizatioll plate. Open reduction 0/ tile radius had realigned the uillar diaphysis and the radial fixa tioll should provide sufficie nt support for IIncomplicated healing o/ the IIlna.

PRACTICAL TIP When using a craniomedial approach, the extensor muscles are forced laterally during plate application, which often results in varus angulation of the distal fragment. A cranial approach (see Figure 16.22) to the distal screw holes may help to avoid this. WARNING When drilling holes in the proximal radial diaphysis, care must be taken not to burst through the transcortex and strike the side of the ulna. This would inevitably result in a broken drill bit. Screws should not he allowed to penetrate both the radius and ulna. In the young animal this will interfere with the normal growth and may result in elbow incongruity and angular limb deformity. In older animals it may result in complications such as implant failure and synostosis.

Wound Closure Routine. Periosteum and deep fascia can be closed as one layer. Post-operative Care A Robert Jones bandage is applied for a few days to limit swelling. Exercise should be controlled for 4 to 6 weeks.

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OPERATIVE TECHNIQUE 16.6 VetBooks.ir

External fixation of radial diaphyseal fractures

Positioning Dorsal recumbency with the contralateral limb pulled caudally and secured. When working alone, or in cases where a closed or limited open approach is planned, it is easiest to suspend the patient from the affected limb throughout the operation.

Assistant Ideally.

Tray Extras Appropriateextemal fixator set; Ellis pins (2 mm for cats and small dogs, 3 mm for medium dogs, 4 mm for large and giant breeds); clamps; connecting bars; large pin cutters (or hack saw); spanners; air or electric drill and bits; chuck and key; drill guides; periosteal elevator; pointed reduction forceps; Gelpi self-retaining retractors. Approach A craniomedial approach to the fractured radius is used, if required. Reduction and Fixation The fracture is reduced using similar techniques to those described in Operative Technique 16.5.

External fixation is usually applied to the medial radius as the distal two-thirds of the medial aspect of the radius represent a safe corridor for pin insertion (Marti and Miller, 1994). However, the radius is flattened in the mediolateral plane, making pin insertion from this direction more difficult. Maximum bone purchase is achieved by directing pins in an oblique craniomedial to caudolateral plane.

(a) Figure 16.21: (a) Schematic view a/the radius to show placement of Q unilateral mediaL exrernaLjixator. A lag screw has also been placed across the oblique radialfracIIlre. This lVould be inserted/allowing/racture reduction via a limited

craniomedial approach. (b) Repair of a comminuted radills alld ulllar fracture in a 20 kg Border Collie. The radills was reduced via a limited craniomedial approach and interJragmentary lag screws inserted. The two major

fragments were then supported with a bilateralul1ipJal1ar jixator (modified type II, see Chapter 9).

Open pin placement is recommended for the medial aspect of the proximal radius as pin insertion in this area can be difficult and unsafe (Marti and Miller, 1994). The pins should be placed between the flexor muscle bellies and this is achieved by directing the pins slightly obliquely in a caudomedial to craniolateral plane.

A unilateral external fixator is applied to the medial aspect of the radius generally with three pins in the proximal fragment and three pins in the distal fragm ent (Figure 16.21a). If the proximal fragment will not accommodate three pins then the proximal part of the connecting bar may be bent caudally so that pins can be placed in the proximal ulna. Where there is a short distal fragment a biplanar frame may be constructed and distal pins may be driven between the extensor tendons in a cranial orientation. Bilateral uniplanar frames may also be used with this type of fracture. .' Unstable comminuted or open fractures often require bilateral (Figure 16.21b) or biplanar frames. Other designs, such as lateral frame orientation for proximal radial fractures and cranial orientation for small bones, ha ve also been advocated (Egger, 1990).

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External fixation of radial diaphyseal fractures

Wound Closure Routine. Post-operative Care Non-adhesive, semi-occlusive dressings should be placed around the fixator pins. The area between the skin and connecting bar is padded out with cotton wool and a Robert Jones bandage is applied over the limb and fixator, including the foot. The bandage is left in position for2 to 3 days to contro l swelling. When the bandage is removed the clamps and pin ends should be protected with Vetrap. Controlled exercise is required while th e fixator is in place. Th e frame should be c hec ked wee kl y and the limb rad iograp he d at 6 weeks. The fixator may be removed or destaged at this time, depending on fracture healing (see Chapter 5).

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OPERATIVE TECHNIQUE 16.7 VetBooks.ir

Salter-Harris fractures of the distal metaphyseal growth plates

Positioning Dorsal recumbency with the affected limb free and the contralateral limb pulied ca udaliy and secured. Assistallt Not essential. Tray Extras Pin/wire cutters; chuck and key (or air/electric drili and bits); wire bender; Gelpi self-retaining retractors; K-wires. App/'oach A cranial approach to the distal radius is made (Figure 16.22). Common digital extensor m.

Abductor policis longu s m.

Extensor carpi rad iali s m.

Figure 16.22:

Crallial exposure of the distal radius.

R eduction and Fixation The antebrachium is grasped whilst the carpus is fl exed and is used as a handle. Traction is exerted and the fracture ends are toggled together and manipulated until alignment is achieved.

WARNING Care should be taken to minimize trauma to the growth plate during reduction.

(a)

(b)

Figure 16.23: Two configuratiolls/or K-\Vire repair ola Type J Salter- Harris/racture o/the distal radius: (a) crossed; (b) parallel.

The fracture is stabi lized with a smali K-wire driven from the medial styloid process, across the fracture, to anchor in the lateral cortex of the radial metaphysis. Often tlus is sufficient to provide fracture stability. However, when the ulna is involved, a second K-wire directed across the fractu re from the lateral styloid process may further improve stability (Figure 16.23a). An alternative method is to place the K-wires paraliel and perpendicular to the fracture surface (Figure 16.23b) .

•

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Salter-Harris fractures of the distal metaphyseal growth plates

Wound Closure Routine. Post-operative Care The limb should be supported in a Robert Jones bandage for I to 2 weeks and exercise is restricted for 3 to 4 weeks. Healing is usually rapid and K-wires are removed from 4 weeks post-operatively.

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OPERATIVE TECHNIQUE 16.8 VetBooks.ir

Styloid fractures

Positiolling Dorsal recumbency with the affected limb free and the contralateral limb pulled caudally and secured. Assistant Not essential.

Tray Extras Pin/wire cutters; chuck and key (or air/electric drill and drill bits); wire bender; Gelpi self-retaining retractors; K-wires~

cerclage wire for tension band; ± plating equipment.

Approach A lateral or medial approach is made depending on the fracture site. Reduction and Fixation These fractures are usua lly reduced easil y by applying a varus or valgus ang ulation towards the

«(/)

(b)

fracture site.

Pin and tension-band wire techniques are lI sed to stabi li ze these fractures. One or two K-wires are used, depending on the size of the avulsed fragment. The Kwires are hand- or power-driven across th e fracture

site into the far cortex . For ulnar avulsions a single Kwire is either inserted into the ulna or directed

obliquely into the distal rad ius (Figure 16.24). Forthe radi us, pins are dri ven obliquely to engage the lateral

cortex. The tension-band wire is placed around the pin end(s) and through a hole 1 or 2 cm proximal to the fract ure site. The wire is tightened and the pins are cut, bent over, and buried in the collateral ligament.

~ (rj \ ~ ~ ~

'I'

Figure 16.24: Two options/or pill positioning ill tlte repair o/ulnar styloid fractures: (a) imo the ullla; (b) obliquely illto the distal radius.

If the fragments are too small to permit pin insertion, the li gament may be reattached to the bone using a screw and spiked plastic washer. Alternatively, the small fragments are removed and the ligament is sutured to a screw and washer placed in the styloid process. The ligament repair is further buttressed with wire or nonabsorbable suture placed through bone tUlIDels or around screws and washers in the styloid processes and ulnar/radial carpal bones (Miller, 1994).

Woulld Closure Routine.

Post-operative Care The limb should be supported in a Robert Jones bandage for 1 to 2 weeks, or longer, depending on the strength of the repair. Exercise is restricted for 4 to 6 weeks. Pin and wire removal is indicated if they become loose or irritate the soft tissues once the fracture has healed.

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CHAPTERSEVENTEEN---------------------------------

VetBooks.ir

The Pelvis and Sacroiliac Joint Marvin L. Olmstead

CONSIDERATIONS IN PATIENT EVALUATION

INTRODUCTION About 25 % of all fractures in dogs and cats involve the pelvis (Brinker, 1975). The high prevalence of fractures involving thi s bone means veterinary surgeons must be ab le to select satisfactory treatment opti ons for many different types of fracture. The choices range from non-surgical patient management to the recon-

structi on of specific pelvic fractures. The treatment plan adopted will depend on: The convalescent care needed The comfort of the patient The severity of fragment displacement The location of the fracture The degree of pelvic canal compromise present. Pelvic fractures are most commonly associated with moto r vehicle trauma (Betts, 1993; Denn y, 1978). The forces creating a pelvic fracture can come from many different angles and ha ve va ri ed magnitudes; therefo re pelvic fractures can occur with many different configurat ions. It is almost impossible to have a single fracture in the pelvis because of its intercon nected, box-like configuration. An animal hit directly from behind may have shear fractures in both ilial wings or bilateral sacroiliac luxations, or a combinati on of an ilial fracture and a sacroiliac lu xa ti on. A fo rce from the s ide may drive the head of the fem ur into the acetabulum, creating fractures in the acetabulum, ilium and pelvic floor with medi al dis placement of the fra gments. Since the possible combinations of

fracture configurations are many it is critical to assess the pelvis fully , through physical and radiographic examination . However, total pati ent eva luation is

paramount . WARNING Almost half of all dogs with pelvic trauma caused by a motor vehicle will have thoracic injuries.

Dogs and cats with pelvic fractures generall y present with a history of an acute onset ofiameness, usually nonweight-bearing, in one or both hindlimbs (Betts, 1993; Brinker ef ai., 1990). In some animals the lameness is mild even though the fractures appear radiographically to be moderate or severe. Following a general physical examination to establish the patient's current health status, a complete orthopaedic examinati on should be performed. Careful digital rectal palpation of the pelvic canal is indicated when a pelvic fracture is suspected. This should be performed as an isolated examination and in conjunction with a passive range of moti on manipulations of the coxofemoral joint. The degree of canal narrowing and the location of fractures and bone frag ments should be carefull y assessed throughout the canal 's circumference.

External palpati on may also provide useful info rmation. Sacroiliac lu xat io ns and iliac fractures may be palpated as unstab le bone segments or may cause disruption of normal anato mica l re lations hips between the spine, pelvis and proximal femur. If an acetabular fracture is present, the relationship between the ischium and greater trochanter is often abnormal. The femoral head may have been driven into the acetabulum, displaci ng the trochanter medially, orif a concomitant ilial shaft fracture exists there may be cranial displacement of the trochanter. WARNING An acetabular fracture can be present without a pain response to manipulation of the hip joint. Definitivediagnosis is established through radiographs of the pelvis. The two standard rad iographic views of the pelvis for evaluating fractures are the ventrodorsal and lateral views. Sometimes, an oblique view of the hemi-pelvis is necessary for better definiti o n of fracture lines and fragment positio n. It may reveal fragment displacement not seen on standard views.

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MANAGEMENT Surgical or non-surgical?

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The decision to treat these injuries non-surgically or surgically is based on: Factors relating to the fracture The effect that malpositioned fragments will ha ve on the patient The length and quality of the expected convalescent period The patient's comfort. Fractures that are relatively non-displaced, stable and not painful, and that do not affect a vital structure or body function , may be treated with cage rest and proper nursing care. Compared with the surgically treated patient, a non-surgically treated patient might have more exte nsive nursing care needs, require addi-

tional physical therapy and have a prolonged recovery period. The objectives of surgical treatment of pelvic fractures are:

To re-establish normal load transmission pathways between the limb and the spine To restore the pelvic canal To re-establish the acetabulum's articular surface To shorten the patient's convalescent time.

after 2 or 3 weeks of cage rest. If the ilial wing is markedly displaced the locomoti ve capability of the hindlimb and the load transmission between the pelvis and spine can be directly affected (Figure 17.1). The patient's convalescent period will be greatly reduced if an unstable or painful sacroi liac luxation/fracture is surgica lly stabilized. Either a lag screw or a trans-ilial pin can be used to stabilize a sacroiliac luxation (Operative Technique 17.1).

ILIAL SHAFT FRACTURES Ilial fractures are more frequently treated surgically than are sacroiliac luxation/fractures. The ilium is

often displaced mediall y, compromising the pelvic canal and endangering the sciatic nerve and other structures in the canal (Figure 17.2). The ilium is important in transmitting loads between the hindlimb and the spine during weight bearing. Repair of ilial fractures decreases pain and thus reduces convalescent

time (Operative Technique 17.2). Patients will recover locomotor function more quickly if fractures of the ilium or acetabulum are stabilized. Only in patients with minimal or non-displaced ilial or acetabular fractures and already walking should non-surgical treatment be considered.

SACROILIAC LUXATIONS Sacroiliac luxations are treated surgically if they are very unstable, markedly displaced or painful (Tarvin and Lenehan, 1990). A minimally displaced sacroiliac luxation will stabilize adequately with fibrous tissue

Figure 17.2: Ventro -dorsal pelvic radiograph showing bilateral ilialfractures in a dog. The pelvic canal and limb load trallsmissiollfrom the pelvis to the spine have both been compromised. The dog could IlOt bear weight on either limb. 111 the post-operative radiograph, the fractures have been reduced via lateral approaches and stabilized using bone plates. Although 011 this view the left-hand plate appears to be compromising the acetabulum, the lateral view showed th is was not the case.

Figure 17.1: A pre-operative ventrodorsal pelvic radiograph showing bilateral sacroiliac luxation and a right acetabular fractu re. There is marked displacement of the iliac wings. The dog was unable to bear weight 011 either limb. The postoperative radiograph shows reduction of the sacroiliac luxatiolls alld stabilization using lag screws and a trans-ilial pin. The acetabular fracture was stabilized with a dorsally positioned bone plate.

ACETABULUM The acetabulum contains one of the articular surfaces of the coxofemoral joint. The principles of joint fracture repair dictate that the joint surface must be anatomically reconstructed to minimize the risk of the joint developing osteoarthritis (Figure 17.1). The weight-bearing

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surface of the acetabulum (its cranial two-thirds) must be reconstructed if its integrity is to be maintained (Operati ve Technique 17.3). Repair of fractures in the caudal one-thi rd of the acetabulum is controversial. Although unrepaired fractures in this area will result in coxofemoral osteoarthritis (Boudrieau and Kleine, 1988), it has not been defini ti vely proved that repairing frac-

219

that generall y hold any bone fragments in re lati ve position. Fragments are seldom displaced in a ma nner that compromises vital structures. If there is marked ischia l fragment rotation or displacement due to muscle pull or wide separation of pubic fragments with an unstable pelvic floor, surgical stabilization with wire, pins and/or lag screws may be needed.

tures in this area will improve the patient 's recovery.

Osteoarthritis may be present but limb function may be unaffected. Due to their small size, fractures of the caudal one-third of the acetabulum can be difficult to stabilize adequately. Wi th a caudal fracture the sciatic nerve is at greater risk of injury during surgery than when the fracnlCe is located more cranially.

CONCURRENT ILIAL AND

ACETABULAR FRACTURE When a fracture of both the ilium and the acetabulum are present, it is pre ferable to repair the ilial shaft first. Repair of the ilium is often done with a stronger fixation system than is used on the acetab ulum because usually more screws and a longer, stronger plate can be applied to the ilium. The reconstruction of the ilium does not have to be as anatomically exact as reconstruction of the acetabulum . When the acetabulum is repaired last, it will be fixed to a solidly stabilized ilial segment. Also, its fi xation will not be subjected to addi tion loads that would be generated during manipulation ofthe ilial fragments if the ilium were fixed last.

ISCHIUM AND PUBIS The pubis and ischi um do not directly transmit loads during weight bearing and are surrounded by muscles

REFERENCES AND FURTHER READING BcttsCW ( 1993) Pelvic fra ctures. in: TexlbookojSmall Animal Surgery. 211d cdll , ed. D Slatter, p. 1769. WB Saunders, Philadel phia. Boudricau RJ and Kleine U (1 988) Nonsurgically managed caudal acctabularfracturcs in dogs: 15 cases( J979- 1984). Joumal a/the American Veterinary Medical Associalioll 193,70 1. BrinkcrWO ( 1975) Fract urcsofth c pelvis. In: Ca nine Surge ry,2 I1dedll , cd. J Archibald, p. 987. American V eterinary Publications, Santa

Barhara . Brinker WO and Braden TO ( 1984) Pelvic fractu res. In: Mallllal of Internal Fixatioll ill 5111011 Allilllals, ed. WO Brinker, RB Hahn and WD Prieur, p. 152. Springer Verlag, Berlin. Bri nker WO, Piemlallei DL and Flo GL ( 1990) Fractures of the pelvis. In: Halldbook of Small Allimal Orthopedics alld Fracture Treatmel/t, 211d edll, p.76. WB Saunders, Philadelphia. Decamp CE and Braden TO ( 1985a) The anatomy of the canine sacrum for lag screw fi xation of the sacroi liac joint. VeterillarySurgery 14, 13 1. Decamp CE and Braden TO ( 1985b) Sacroiliac fracture-sepurations in the dog. A study of 92 cases. Veterinary Surgery 14, 127. Denny HR (1978) Pelvic fractures in the dog: a review of 123 cases. Jou rnal of Small Allimal Practice 19, 151 . Olmstead ML (1 990) Surgica l rcpairofacetabular fractu res. ln: C/l rrem Techlliques in Small Allimal Surgery, 3rd edll , ed. MJ Bojrab, p. 656. Lea and Fcbigcr, Philadelphia. Piennatlci DL (1993) The hind limb. In: All Atlas of Surgical Approaches of the BOlles of the Dog alld Cat, 3rd edn, p.264 . WB Saunders, Philadelphia. Slocum Band Hohn RB ( 1975) A surgical approach to the caudal aspect of the acetabulum and body of the ischium in the dog. Journal ofthe American Veteril1ary Medical AssociQ[ion65, 167. Tarvin GB and Lenehan TM (1990) Management of sacroiliac dislocalions and ilial fra ctures. In: Current Techniques ill Small Allilllal Surgery,3rd edll, ed. MJ Bojrab, p. 649. Lea and Febigcr, Philadelphia.

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OPERATIVE TECHNIQUE 17.1 VetBooks.ir

Sacroiliac luxations

Positioning On the sternum with hind limbs straddling sandbags or a positioning pad (Figure 17.3). Positioning the animal in this manner makes manipulation and visualization of the bone fragments easier in most cases. Figure 17.3: Patiellf positioning/or surgical repair a/sacroiliac luxation/fracture. The hindquarters Gre elevated by the pads. A dorsaL midline approach is used to expose the sacroiliac area.

Assistant Essential for maintaining exposure of the sacrum with a Hohmann retractor while the surgeon drills the thread hole for the lag screw (see below). The rest of the surgery can be done with either self-retaining retractors or assistant-held retractors. Tray Extras For lag-screw technique: appropriate screw set and necessary drill bits ± tap; drill; periosteal elevator; Hohmann retractor. For trans-ilial pin technique: appropriate size pin; chuck; large pin cutters. For both techniques: Kern bone-holding forceps; hand-held or self-retaining retractors (e.g. Gelpi). Surgical Approach A dorsal midline approach is used to expose sacroiliac luxation/fractures. The dorsal back muscles are reflected laterally off the spinous processes of L6, L7 and the sacrum. The lateral surface of the sacrum is exposed and the dorsal aspect of the displaced ilium is identified. Alternatively, the lateral sacrum can be approached via an incision over the iliac spine, with subsequent dissection down between the epaxial muscles and the medial aspect of the ilium (piermattei, 1993). The midline approach is the author's preference for both of the repair tecJmiques described below, but either approach is equally satisfactory. The midline approach facilitates trans-i1ial pinning. Reduction and Fixation

Lag screw The thread hole is drilled in the body of the sacrum before the i1ial segment is reduced. The lateral surface of the sacrum is exposed and the ilial wing is displaced ventrally by placing the tip of a Hohmann retractor under the ventral point of the sacrum. The thread hole in the sacrum should be placed in the centre of the exposed sacral surface, thus placing the screw in the ma ximum available bone. A slight ventral angulation of the thread hole's position ensures the screw 's position in bone and out of the neural canal (Figure 17.4) (DeCamp and Braden, 1985a,b).

Drill and drill guide

Hohmann retractor

Figure 17.4: POSitioning the screw hole duril1g repair of sacroiliac luxatiolls. Th e thread hole is started in the cenrre of the sacrum and angLed sLightly ventrally to miss the neural callal. The lateral surface of the sacrum is exposed by levering the ilium ventrally.

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OPERATIVE TECHNIQUE 17.1 (CONTINUED) VetBooks.ir

Sacroiliac luxations

The caudal portion of the middle glutea l muscle is reflected off its origin along the caudal dorsa l ili ac spine and the lateral s urface of the ilium is exposed. The sacral articulation on the medi al iliac surface is identified visuall y and/or with palpation. A glide hole is drilled from lateral to medial, exiting the centre of the ilium's sacral arti culatio n. The ilium is reduced by grasping the cauda l dorsal iliac spine with a bone reducti on forceps with fixati on teeth, such as a Kern bone clamp, and manipulat ing the ilium into near anatomical position. A space is left between the ilium and the sacrum so placement of the screw in the thread hole can be visual ized. The appropriate sized screw is inserted through the glide hole. The screw is manipulated into position until its tip is in the thread hole. Tightening the screw will red uce the luxation (Figure 17.5) . If the sacrum is large enough, a second lag screw orsmall pin is inserted into the sacrum to prevent rotation of the fragments .

............ .,

\.. ~fttt11J:!tt;;;::_.-J"1 ...........

Figure J 7.5: Screw position/or fixQrion of sacroiliac luxarions. Drill a glide hole through tlte ilium. Digital palpation of the articular surface on the medial ilial wall guides the position oj the glide hole. Th e screw is pushed partially through the glide hole be/ore the luxation is reduced, so tllat its engagement with the thread hole in file sacrum can be visualized. Fully tightening the screw reduces the luxation.

WARNING Positioning the thread hole outside the sacrum 's centre Dlay place the screw in a thin part of the bone Ot· in the neural canal. T r ans-i1ial pin To reduce the ilium, pointed reduction forceps are positioned with one point in the caudal sacrum and one point in the lateral ilial surface and the clamp is ti ghtened. The fu lly tightened clamp will hold the ilium and sacrum in reduction willie the trans-ilial pin is applied. Because this reduction technique closes the space between the ilium and sacrum it call1ot be used with the lag screw technique described above. Once the lu xation/fracture is reduced, the trans-i lial pin can be inserted. The pin selected for fixation should be easil y bent and no larger than 3 mm in diameter. The selected pin is dri ven by hand lateral to medially through the ilium on the side of the injury. The pin should pass dorsal to the 7th lumbar vertebra at the level of the base of the dorsa l spinous process. It can pass either through the dorsal spinous process or just caudal to it. Once the pin is pastthedorsal spinous process, the hand chuck dri ving the pin is elevated, which lowers the pin's point. The pin is driven medial to lateral through the opposite ilium and the nUddle gluteal muscle until just enough of its point is exposed to be grasped. The pin should not penetrate the skin . The pin is bent dorsa ll y as it is advanced. When the pin is advanced far enough, it is bent 900 and is cut off, leaving a bend at the end. The pin is pulled back until the bend is buried in the gluteal muscle over the ilium opposite the injured side. The pin on the injured side is bent dorsally 900 and cut off. The pin now has hooks on both ends that prevent migration (Figure 17.6). If desired, a second trans-ilial pin can be inserted in the same maImer. Figure 17.6: Tralls-iliaL pill stabilization 0/ sacroiliac [uxations. Th e tralls- iliai pill passes through the wing ofeach iliulII and dorsal to the 7th lumbar vertebra. The ends o/the pill are hem TO prevellf migration.

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Sacroiliac luxations

Post-operative Care The animal should be placed on limited activity for 4 to 8 weeks. No activity more strenuous than a walk is allowed during this period. Towel or sling support of the hindquarters is provided as necessary. Supply soft bedding to prevent pressure sores developing. Urine and faecal soiling of the patient are cleaned as required.

PRACTICAL TIP If the sacroiliac luxation/fractUl'e is accom panied by an ilial fracture on the opposite side, the ilial fracture should be stabilized first as this alone may result in reduction and adequate stability of the sacroiliac joint, because of the box configuration of tbe pelvis,

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OPERATIVE TECHNIQUE 17.2 VetBooks.ir

lIial shaft fractures

Positioning Lateral recumbency . Assistant Helpful for maintaining ex posure and reduction of the ilium while the surgeon implants the bone plate. Tray Extras Appropriate bone plate and screw set including drill bits ± taps; drill; bone-holding forceps; self-retainingand hand-held retractors; periosteal elevator. Surgical Approach A lateral approach is used. The ventral margin of the middle and deep gluteal muscles is isolated and the muscles are elevated off the face of the ilium to the extent needed in the fracture repair (Figure 17.7).

Superficial gluteal m.

Cranial gluteal artery, vein and nerve

Figure 17.7: Exposure a/ the lateral surface a/the ilium .

Deep gluteal

~~i~~~~il-C~ Iliacus m.

Biceps femoris m.

Sartorius m.

Tensor fascia latae m.

Reduction WARNING I1ial fragment reduction ean be the most dimeult part of the surgery. Often the free segment of the pelvis is displaced cranially and/or mediall y. The fragment should be lateralized first and, if necessary, moved caudally. If the fracture segments are collapsed mediall y, either a Lahey retractor or a pair of Kern bone forceps is helpful in repositioning the fragments laterally. A Lahey retractor, which.is blunt, strong, and bent 90° at its end, is passed along the medial wall ofthe free segment. The retractor's tip is maintained on the bone's surface as it is passed along the medial wall to avoid compromising the sciatic nerve. Pulling laterally with the retractor's handle moves the fracture segments laterally (Figure 17.8) .

•

Sciatic nerve

Figure 17.8: Reduction of ilial shaft fractu res. Medialiy displaced pelvic fracture fragments can be moved laterally by placing the blunt blade oj a Lahey refractor along thefragment's medial walL alld pulling laterally.

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Lahey retractor

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I1ial shaft fractures

If the fragment is large enough, Kern bone-holding forceps can be clamped along the ventral edge of the free ilial shaft, allowing the fragment to be manipulated (Figure 17.9) . If an ilial segment is cranially displaced then a self-centring reduction clamp can be placed with one holding surface of the clamp on the secure cranial frag ment and the other holding surface on the free caudal fragment. Closing this clamp will move the free fragment caudall y (Figure 17.10). Some reduction techniques discussed for reducing acetabular fractures are also helpful in reducing ilial shaft fractures when no acetabular fracture exists. I1ial shaft alignment can be slightl y off and still give a satisfactory final result. Reduction of the ilial fracture can almost always be maintained temporarily by positioning self-centring or Kern bone clamps dorsal to ventral across the fracture segments.

Figure 17.9: Reductiol1 ofilial shaft fractures. The Kem bone clamp '5 configuration provides tlVO points of fixation in the caudal free ilia/fragment. This allows the

fragment to be manipulated into proper alignment.

PRACTICAL TIP After the ilial fracture has been reduced, the most effective way of stabilizing the fracture is bone plating,

Figure 17.10: Reduction ofilial shaft/ractures. A self-

centring clamp call be llsed to reduce free ilial segmellfs. One blade a/the clamp is placed 011 the ilium '5 dorsal rim while the other blade is placed all the ventral rilll a/the freefragmem. Closing the clamp will brillg the/ree

segment to the fixed segmem. Reduction is maintained with the self-centring clamp while a bone plate is applied.

Fixation Several types of plates developed by the AO{ASIF group can be used, depending on the size of the animal and the degree of comminution of the fracture. For ilial fractures, mini-fragment T or L plates or standard Dynamic Compression Plates, which accept 3.5, 2.7 or 2.0 mm screws, are available. The size offragments will govern the size of implant used. For ilial shaft fractures the plates must be contoured to the concave shape of the lateral surface of the ilium. If possible at least three screws should be placed in each fracture segment. If the screws are placed in the caudal fragment first, the plate will aid in reduction of the fracture when the screws are tightened in the cranial segment (Figure 17.11) (Brinker and Braden, 1984). If the fra cture is reduced and minimal collapse is present, the screws nearest the fracture line are placed first, one each in the caudal and cranial fragments. The remaining screws are inserted alternately on either side of the fracture from nearest to furthest from the fracture line. Figure 17.11: Platefixatioll ojiiialfractures. Screws placed ill the bone plate in the order il/dicaled willlllove thejree caudal ilial segment laterally.

Post-operative Care As for Operating Teclmique 17.!. The activity levels of these patients must be strictly limited to reduce the chance that the fragments will change position during the convalescent period.

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OPERATIVE TECHNIQUE 17.3 VetBooks.ir

Acetabular fractures

Positioning Lateral recumbency.

Assistant In most cases, an assistant is required to maintain exposure and reduction of the acetabular fracture while th e surgeon implants th e bone plate.

Tray Extras Appropriate bone plate and screw set, including drill bits ± taps; drill; bone-holding forceps; self- retaining and hand-held retractors; periosteal elevator.

Sllrgical Approaches Acetabular fractures are approached either by a trochanteric osteotomy or by a ca udal approach (S loc um and Hohn, 1975; Olmstead, 1990; Piermattei, 1993) . T he author o nl y uses the trochanteric osteoto my when wider ex posure o f the cranial pelvis is needed for fracture repair, as when the i1ial shaft and the acetabu lum are both fractured on the same s ide.

WARNING The sciatic nerve must be protected. Trochanteric osteotomy The superfi cial gluteal muscle is isolated, incised at its insertion and refl ected dorsally. The osteotomy of the greater trochanter is perfonned starting at the level o f the third trochanter and extending dorsally to the junction of the greater trochanter and the femora l neck. The middle and deep g luteal muscles, still attac hed to th e greater trochanter, are refl ected dorsally (Figure 17.12). T he caudal portion of the deep g luteal and the gemellus muscles are elevated with a periosteal elevator from their origin over the dorsal rim of the acetabulum, exposing the fracture site.

':~~~;:;;::~::::r gluteal superfiCial m.

,..

~-f~__----1r-t- Deep

& middle gluteal m.

Osteotomy of greater

--'lM-'I~tt~-J-+- lIium

trochanter f+----/-,f-I+\-ff~~~~\1;:;;\\i_1-Sciatic nerve

Vastus Rectus femoris m.

lateralis m.

Biceps femoris m.

(retracted)

Figure 17.12: The trochallleric osteotomy exposes/raclllres 0/ the acetabulum. The sciatic lieI've should be isolated be/ore the osteotomy is performed. Following repair a/ the acetabulum, the trochanter is reattached with two pillS and a tension-band wire (Figure J i. J 7) .

•

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Acetabular fractures

Caudal approach Superficial Usually, the caudal approach is prefergluteal m. able. It provides exposure ofthe acetabuInternal Deep obturator & lum eq ual to the trochanteric osteotomy, & middle gemelli m. does not require creation of a fracture site gluteal m. in the femur and is more quickl y closed. ~~\f-~-+-+" Fracture The caudal approach also starts with Tensor fascia tenotomy of the superficial gluteal musSciatic n. lalam. cle at its insertion point on the third trochanter. The muscle is tagged with suture and retracted dorsally. The internal obtuBiceps rator and gemelli muscles are incised at their insertion in the trochanteric fossa, ~f?::.....if-J_ femoris m. Vastus tagged, and retracted caudodorsally, prolateralis m. viding exposure of the caudal acetabulum and protection for the sciatic nerve. The caudal portion of the deep gluteal and gemellus muscles are elevated until the entire dorsal rim of the acetabulum is exposed. The caudal aspect of the ilium Figure 17.13: Caudal approach to rile can be exposed by inserting the tip of a acetabulum. The externaL rotators oj Hohmann retractor just cranial to the ven- the hip are incised at their trochanteric tral border of the ilium under the middle fossa insertion. These muscles are and the deep gluteal muscles. The retrac- retracted caudally to protect the sciatic tor displaces the middle and deep gluteal nerve. Extension and internal rotation a/the/emur enhances the exposure. A muscles distally. Maintaining the hip in Hohmann retractor placed under the an extended and internally rotated posi- middle alld deep gluteal muscles alld tion provides maximal exposure to the hooked 011 the ventraL edge of the iLium retracts these muscles ventrally. acetabular rim (Figure 17.13).

7....

Reductioll Because the acetabulum is a joint surface, it must be completely reduced anatomically if a successful outcome is to be achieved. In addition to the techniques discussed below, some of the techniques used for reducing ilial fractures (Operative Technique 17.2) can also be used for reducing acetabular fractures. The caudal bone segment of an acetabular fracture is often displaced cranially. The fragment can be brought into a more caudal position by two different methods. These methods are also used to provide traction on an ilial fragment that is being difficult to move when the acetabulum is not fractured. In the first method, an intramedullary pin is driven with a pin chuck ventral to dorsal through the ischium just cranial to the ischial rim. During this procedure, the hip joint should be fl exed. The pin should penetrate the s kin on either side of the ischium. If a second pin chuck is attached to the portion of the pin exposed dorsally, the two pin chucks can be used as handles to pull the fracture segment caudally (Figure 17.14). Rotation of the segment can also be provided with this method, although s ince there is only a single point offixation in the fragment the amount of rotation achieved is limited.

Intramedullary

Hip flexed

Figure 17.14: An intramedullary pin drivell through the ischium is used to apply caudal traction to a free pelvic segment. Flexing the hip while driving the pill moves the hamstring muscles out of the way.

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Acetabular fractures

The second method for providing caudal traction uses a large Kern bone-holding clamp. An incision wide enough to allow insertion of the end of the Kern bone-holding clamp is made parallel with the ischial rim. Because the fixation teeth of the Kern clamp prov ide four points of fixati on, this instrument can be used for both caudal retraction and Kern rotation of the segment (Figure 17.15). Large Kern Forceps clamps are used in most moderate and all large dogs because small Kern clamps do not have a long enough lever arm to manipulate the fracnlfe segment easily. Figure 17.15: A Kern bOlle-holding clamp is applied Acetabular fracture reduction is maintained with to [he ischium through all incision over the tuber pointed reduction bone forceps, or by manuall y holdischia allowing the free segmem to be rotaled and retracted caudally. ing the fragments in place until the permanent stabilization procedure is completed. Reduction of an acetabular surface can be checked by placing ventral traction on the greater trochanter. This will pull the femoral head out of the acetabulum enough for the articular rim of the acetabulum to be observed through an incision in the joint capsule or an existing tear.

Fixation Although non-plating surgical techniques have been described for repair of acetabular fractures, none ofthem has proved to be as effective as bone plates or has provided the clinical results that bone plates have. Two different sizes of C-shaped acetabular plates from the AO/ASIF group (S ynthes Ltd) are effecti ve in the treatment of simple acetabular fractures. Miniature fragment plates and standard Dynamic Compression Plates® (Synthes, Ltd) have been used to stabilize acetabular fractures. Some surgeons prefer to use the reconstruction plate for acetabular fractures because it can be bent in several different planes. PRACTICAL TIP The bone fragments will shift in position as the screws are tightened if the plate is not perfectly contoured to the dorsal surface of the acetabulum. The C-shaped acetabular plates are easy to contour to the acetabulum's dorsal bone surface because of their shape. Mini plates are easy to bend because they are thin. However, this makes them relatively wea k and limits the size of animal in which they can be used. The dorsal surface is used fo r plate placement because adequate bone is present there and this is the tension surface of the bone (Figure 17.16). In all acetabular fractures at least two screws should be located on either side of the fracture line, and they should be angled so that they do not penetrate the articular cartilage surface (Figure 17.16). It is sometimes helpful to bend the plate before surgery, using a model of an intact pelvis that is approximately the same size as the pelvis that needs repair. The pre-bent plate can be sterili zed and minor contouring adjustments made during surgery. TI,is tecllnique reduces surgical time.

Figure 17.16: BOlle plates are p laced over the dorsal rim, wh ich is the most accessible area oj the acetabulum, has the largest visible bone surface alld is the acetabulum's lension surface. The clit-away view shows the bone screw directed properly through the plate so thar the a rticular surface is nor violated.

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Acetabular fractures

One of the most difficult fractures to stabilize is one that has a component of the medial wall of the acetabulum fractured out. If a large section of this wall is involved, the femoral head will displace medially into the pelvic canal. If the fracture segment containing the medial wall extends far enough cranially, lag screw and/or intramedullary pin fixation of the ilial segment should be done to stabilize the fragment. If the fragment cannot be stabilized, a slight over-bending of the plate closing the diameter of the articular surface makes it more difficult for the femoral head to displace medially. If the femoral head cannot be prevented from displacing medially, a salvage procedure, the excision arthroplasty, should be considered. Excision arthroplasty may also be performed for severe fractures where reconstruction is not possible. This procedure is done only as a last resort as it sacrifices joint function but is intended to save limb function. If an acetabular malunion from an untreated acetabular fracture has resulted in osteoarthritis in a dog over 14 kg, a total hip replacement may be considered.

Acetabular

plate

Tension band wire

Intramedullary

pins

Figure 17.17: Fixation of a trochanteric osteotomy using two pins and a tension-band wire.

Closure If osteotomy was performed, the greater trochanter is reattached to the proximal femur with the tension-band technique (Figure 17.17). After caudal approach, the internal obturator and gemelli muscles are sutured to fascial tissue near their original insertion point. The remaining tissues are routinely closed. Post-operative Care As for Operative Technique 17.1.

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CHAPTER EIGHTEEN

VetBooks.ir

The Femur A. Colin Stead

INTRODUCTION

may be a consequence. However, several reported seri es of fracture repairs in this area have indicated no cases of avascular necrosis (Daly, 1978; De Camp et aI., 1989; Jeffery. 1989) but thinning and remode lling of the femoral neck is common. The proximal femoral growth plate or physis closes between 6 and 12 months in the dog (Sumner-Smith, 1966) and between 7 and 10 months in the cat (S mith. 1969). Early closure of this growth plate may cause a varus deformity of the hip, while closure of the greater trochanteric growth plate may lead to a valgus deformity of the hip and s ubluxation. Daly (1978) reported cases of early closure with no apparent clinical problems.

Femoral fractures are common in small animal practice. mostly the result of road accident trauma and less commonly as pathological fractures in juveniles with nutritional osteodystrophies and mature animals with bone tumours.

PROXIMAL FEMUR An appreciation of the blood supply of the femoral head and neck is vital to treatment of fractures in this area (Figure 18. 1). Fractures within the joint capsule will disrupt the blood supply and avascular necrosis

Fractures ofthe femoral head and neck These fractures can be classified into five types (Figure 18.2): epiphyseal, physeal, subcapital, intertrochanteric and trochanteric. Epiphyseal The treatmentforthis is surgical (Vernon and Olmstead, 1983) and should be done promptly to minimize damage to the hip joint and the risk of avascular necrosis (Operative Technique 18.1). Physeal, suhcapital and intertrochanteric Prompt surgical treatment is necessary and various techniques have been used: Lag screws (2.0 mm) inserted retrograde from the articular surface (Kuzma et aI., 1989; Tillson et al.. 1994). In a small series reported by Miller and Anderson (1993) some dogs

Figure 18.1: Arterial blood supply to thejemoral head and neck of a dog. A, femoral artery: B, lateral circumflex femoral: C, mediaL circumflex/ellloral; D, caudal gluteaL.

Attachment of joint

Growth plate

capsule Cranial view

Cranial view

Attachment of joint

capsule

caps ule

Cranial view

Figure 18.2: Fractures ofthejemoral head and neck. From the Left, epiphyseal, physeal, subcapital, intertrochanteric and trochanteric.

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Intramedullary pinning (Operative Technique 18.4) Bone plating (Operative Technique 18.5) External fixatio n (Operative Technique 18.6)

Simp le transverse or short oblique fractures in cats and small to med ium sized dogs Selected comminuted shaft fractures in cats

. Fractures of the femoral diaphys is from the subtrochanteric area distally .

which are either comminuted, long oblique, oblique spiral or segmental. Transverse or short oblique fractures in medium to larger dogs

As with the humerus, the femoral shaft is not idea lly suited for using 3n external fixator because of its muscle coverage. However, in situations where anatomical reconstruction is decided against and in open fractures, external fixation ma y be used as part of a minimall y in vasive strategy (see Chapter 10)

Table 18.1 ,' Decision making ill the surg ical management offemoral diaphyseal fra ctures.

remained lame and required an excision arthroplasty Three K-wires inserted from th e subtrochanteric area, described by Jeffery (1989) Lag screws with or without an anti-rotation K -wire from a similar approach (Nunamaker, 1973; Hulse et aI., 1974). Lambrechts et al. (1993) showed ex perimentally that the latter two techniques were th e strongest of th e subtrochanteri c tec hniques. In skeletally mature dogs, th e preferred technique is a subtrochanteric lag screw. In cats and skeleta ll y immature dogs, K-wires are used [Operative Technique 18.2].

Trochanteric Trochanteric fractures are uncommo n and they usually occur in association with separation of the proximal femoral epiph ysis or dislocation of the hip. The technique of choice is two K -wires and a wire tens ion-band (Operative Technique 18.3).

FEMORAL DIAPHYSIS Fractures of the femoral diaph ysis are common and normall y require interna l fi xatio n, th e exceptions being undis placed and impacted shaft fractures and pathologica l fractures associated wi th nutritional bone dystrophies in immature animals, which will heal with rest alo ne. The method of fixation depends on the age and s ize of the animal and th e nature of th e fracture (Table 18. 1).

DISTAL FEMUR Three fracture types occur in this area (Figure 18.3): Fractures involving the distal growth plate Fractures of the distal femoral metaphysis or epiphys is Intercondylar fractures.

Fractures involving the distal femoral growth plate These fractures are common; they are normall y SalterHarris type II in the dog and type I in the cat. Surgical treatment is necessary. Various treatments have been used, but the recommended technique employs either two Rush pins (Lawson, 1959) or crossed K-wires (Milton et at., 1980) (Operative Technique 18.7). Raiha et at. (1993) described the use of biodegradable pol ylactic acid rods used as cross pins, but the technique is not widely used at present. There is a chance that if the implants are removed within 4 weeks an open growth plate may continue to grow, especially if Rush pins are used (Stone et aI., (981). In some instances where early growth plate closure has occurred, compensatory length ening of other bones in the affected limb has been reported (Alcantara and Stead, 1975).

Comminuted diaphyseal fractures in cats In many instan ces, the use of buttress and neutralization plates is indicated; however, Denny (1993) advocates the use of an intramedullary pin plus cerclage wire to tie in the fragments for most comminuted fractures (see Figure 18. 12). An external fixator may also be used.

Salter Harris

Single

Bicondylar

Type I fracture

condylar

fracture

of distal femur

fracture

Figure 18.3: Fractures of the distalfemur.

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A fracture of this type may also be treated with Rush pins or crossed K-wires, as above. An alternative is to use a lag screw into the medial condyle (Denny, 1993) (Operative Technique 18.7).

WARNING A lag screw should not be used in an immature animal.

Intercondylar fractures These are rare. Single or bicondylar fractures occur, and are articular fractures requiring anatomical reduction. If the fracture involves one condyle, or a part of one, fixation is by a single lag screw and anti-rotation K-wire (Carmichael et al., 1989) (Operative Technique 18.8). With bicondylar fractures, the articular fracture is fixed first using a lag screw and then the condyles are re-attached to the femur using two Rush pins or crossed K-wires (Operative Technique 18.7).

REFERENCES AND FURTHER READING Alcantara Pand Stead AC (1975) Fractures of the distal femurin the dog and cat. Journal of SlIIal/ Animal Practice 16, 649- 659. Bassell FH , Wilson J, Allen 8 and Azuma H (\969) Nonna! vascular anatomy of the head of the femur in puppies with emphasis on the inferio r retinac ular vessels. JOllmal of Bone alld i oillf Surgery

5lA, 1139-1153. Cannichacl S, Wheeler SJ and Vaughan LC (1989) Single condylar fractures of the distal femu r in the dog. l oufllal of Small Animal Practice 30,500-504. Chaffee VW (1977) Multiple stacked intramedullary pin fixation of humeral and femoral fractures. lournal of the American Animal Hospital Association 13, 599-601. Dal y WR (1978) Femoral head and neck fractures in the dog and cat. A review of 115 cases. Veterinary Surgery 7, 29-38. De Camp CE, Probst CW and Thomas MW ( 1989) Inte rnal fixati on of femoral capital physeal injuries in dogs, 40 cases 1979-1987. lournal of the American Veterinary Medical Association 194,

1750-1754. Denny HR ( 1971) Simultaneous e piphysea l separation and fracture of the neck and great trochanter in the dog. Journal of Small Allimal Practice 12, 613-621. Denny HR ( 1993) Orthopaedic Surgery ill the Dog alld Cat, 3 rd edn.

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Blackwell Scientific . Hulse DH, Wilson JW and Butler HC (1974) Use of the lag screw principle for stabilization of femoral neck and fe moral capital epiphyseal fractures. lournal of the American AI/imal Hospital Association 10, 29-36. Hulse DH, Abde lbaki YZ and Wilson, J (1981) Revascularisation of fe moral capital physeal fractures following surgical fixation.Journal of Veterinary Orthopaedics 2, 50-57. Jeffery ND (1989) Inte rnal fixation of femoral head and neck fractures in the cat . Journal of Small Animal Practice 30, 674-677. Kaderly RE, Anderson BG and Anderson WD (1983) Intracapsularand intraosseous vascular supply to the mature dog's coxofemo ral joint. Americall Journal of Veterillary Research 44, 1805 - 181 2. Kuzma A, Sumner-Smith G, Mille r C and McLaughlin R (1989) A technique for re pair of fe moral capital epiphyseal fra ctures in the dog. Journal of Small Animal Practice 30 444 -448. LambrechtsN E, Verstraete FJM , Sumne r-Smith G etal. (1993) Inte rnal fixation of femoral neck fractures in the dog - an in vitro st udy. Veterinary and Comparative Orthopaedics alld Traumatology 6,

188- 193. Lawson DD ( 1959) The technique of Rush pinning in fracture repair. Modern Veterinary Practice 40, 32-36. Lee R (1976) Proximal femoral epiphyseal separation in the dog. Journal of Small Allimal Practice 11, 669-679. Marti JM and Miller A (1994) Delimitation of safe corridors for the insertion of external fixator pins in the dog. I: Hindlimb. J Ol/rnal ofSmal! Animal Practice 35, 16-23. Mille r A and Anderson TJ ( 1993) Complications of articular lag screw fixat ion offemoral capital epiphyseal separations. Journal ofSmall Animal Practice 34, 9- 12. Milton JL, Home RD and Goldstein GM (1980) Cross pinning. A simple technique for treatment of certain metaphyseal and physea l fractures of long bo nes. Journal of the American Animal Hospital Association 16, 891-906. Nunamaker DM (l973) Repair of femoral head and neck fractures by illterfragmenta ry compression. Journal of the American Veterinary Medical Association 162,569. Olsson SE, Poulos PW Jr and Ljungre n G ( 1985) Coxa plana vara and femora l capital fractures in the dog. Journal of fhe Americall Animal Hospital Association 21 , 563-57 1. Pie rmallei DL ( 1993)AnAtlas ofSurgical Approaches tolhe BOlles and loints of the Dog and Cat, 3rd edn. WB Saunders, Philade lphia. Raiha IE, Axelson P, Skutnabb K et al. (1993) Fixation of cancellous bone and physeal fractures with biodegradable rods of self reinforced polylactic acid. J Ollrnal ofSmal! Animal Practice 34, 13 1- 138. Smith RN (1969) Fusion of ossification centres in the cat. JOllrnal of Small Allimal Practice 10, 523-530. Stone EA , Betts CW and Rowland GN ( 1981) Effect of Rush pins on the distal fe moral growth plate of young dogs. American lournal of Veterinary Research 42, 261 -265. Sumner-Smith G ( 1966) Observations on epiphyseal fu sion of the canine appendicularskeleton.JollrnalofSmallAnimal Practice 7, 303-3 11 . Tillson DM, McLaughlin RM and Roush JK (1994) Eva luation of e xperime ntal proximal femoral physea l fractures repaired with two cortical screws placed from the articular surface. Veterilla ry and Comparative Orthopaedics alld Traumatology 7, 140- 147. Vernon FF and Olmstead ML (1983) Femoral head fractures resulting ill epiphyseal fragm entation. Resultsofrepairin 5 dogs. Veterinary Su rgery 12, 123- 126.

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Epiphyseal fractures of the femoral head

Positioning Lateral recumbency with affected leg uppermost. Assistant Often desirable to ha ve two assistants - one to manipulate limb and one to retract. Tray Extras 1.5 or 2.0 mm bone screw set; drill bits; Langenbec k retractors; large and small Hohmann retractors; Gelpi self-retaining retractors; small pointed reduction forceps; chuck; K-wires; pin/wire cutters; hammer and flatended pin. Surgical Approach Either a craniolateral approach or a dorsal approach via a trochanteric osteotomy can be used. The craniolateral is regarded as the least traumatic and should be used for all fracture fix ations except where retrograde K-wires are used in the cat. However, Hulse el al. (1981) claimed that trochanteric osteotomy did not disrupt the blood supply to the femoral head and neck. Craniolateral Approach Centre the skin incision over the greater trochanter and continue one-third of the way down the femoral shaft (Figure 18.4). The fascia lata is incised along the cranial edgeofthe biceps femoris muscle. Incise the insertion of the fascia lata over the femur and proximally along its junction with the s uperficial gluteal muscle. Retract the fascia lata cranially and bluntly dissect along the cranial aspect of the femoral neck to clear the joint capsule. The joint capsule is incised longitudinally to minimjze vascular damage, continuing into part of the origin of the vastus muscle below the greater trochanter. Reflect part of the origin of the vastus distally to expose the third trochanter. Tenotomize the crania l one-third of the deep glutea l tendon and incise along the cranial third of the muscle to reflect it and improve the exposure of the femoral neck and head (piermattei, Lateral 1993). Outward rotation of the stifle williaterali ze circumflex femoral the intact portion of the femoral head or neck. vessels Preserve the teres ligament if possible. If it is Articularis essential to cut the Ligament, it may be done with coxae m. fine curved scissors or a Ilip disarticulator. PRACTICAL TIP Applying pointed reduction forceps to the g.'eater trochanter is helpful in manipulation,

Greater trochanter Vastus lateralis m.

Figure 18.4: Exposllre olrlie flip regiol1 via a cral1iolareral approach.

Trochanteric osteotomy approach (See Chapter 17.) After refl ecting the trochanter and the gluteal muscles dorsally, the remains of the deep gluteal muscle are cleared from the joint capsule. Incise the capsule longitudinally to ex pose the femoral neck and head.

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Epiphyseal fractures of the femoral head

Reductioll alld Fixatioll An assistant should rotate the stifle and femoral shaft outwards to laterali ze the femoral head so that the damage can be inspected. One or two Hohmann retractors are placed under the femoral neck to hold it up (Figure 18.5a). If the fragment is large enough, fixation should be done using 1.5 or 2.0 mm lag screws inserted if possible from the dorsal femoral head/neck junction. The fragment needs to be manipulated into position with a small Hohmann and grasped with forceps (on the round ligament if it is attached to the fragment) and held in place with small reduction forceps (Figure IS.5b). It may be necessary to sever the teres ligament in some cases to achieve this. The gliding hole for the lag screw is drilled from lateral to medial, angled as necessary from the femoral head/neck junction. The thread hole is drilled using a centring insert sleeve through the gliding hole. The hole is tapped and a countersink is used so that the head of the screw will be placed below the cartilage surface. Careful drill and screw measurement is necessary to avoid penetration of the articular surface. An anti-rotation K-wire should be inserted, either parallel to the screw or at an angle, also with its head countersunk (Figure 18.5c). This can be done with a hammer and a pin with a flat end. If the fragment of bone is a narrow slice, it will be necessary to insert the lag screw retrograde from the medial surface, if possible via the fovea capitis, ensuring that its head is countersunk. Small fragments may need to be removed, but assess the impact of removal on hip joint func tion. If it will be severely compromised, salvage surgery may be indicated (excision arthroplasty or total hip replacement). WARNING It is most important to minimize joint capsule damage to preserve blood supply. It is also essential that the sciatic nerve is identified and protected from damage. Do not apply pressure to it with a retractor!

•

Middle gluteal

Deep glutemar.U

-H--t'e

Articularis

coxae

Insertion of vastus lateralis m. Vastus lateralis m. (retracted)

(a) Countersunk

Thread hole

glide hole

for lag screw

view (b) Lag screw

Kirschner wire

(e)

Cranial view

Figure 18.5: Exposureandfixatiollojaproximaljemoral epiphyseai fracture (capital/racture ill adults) .. (a) The femur is externally rotated alld Hohmanll retractors are used to elevate the distal segment to allow inspection of the fracture site. (b) Pointed reduction forceps are used to maintaill reductiol/. (c) Lag screw and K- wire!lXarion .

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Epiphyseal fractures of the femoral head

Closure The joint caps ule should be repaired with interrupted sutures of absorbable material. The greater trochanter is re-attached using two K-wires and a wire tension-banel. The gluteal tendon is sutured with mattress sutures ofPOS and the vastus origin is similarly sutured to the deep gluteal. The superfi cial gluteal tendon is repaired with hori zontal mattress sutures ofPOS. The fascia lata is repaired with a continuous suture. The remai nder of the closure is routine. Post-operative Care Six weeks of house confinement and a phased return to acti vity.

0.;.; _

_ __

_ _ _ __

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Physeal, subcapital and intertrochanteric fractures

PositiOllillg

Lateral recumbency with affected leg uppermost. Assistant Often desirable to have two assistants - one to manipulate limb and one to retract.

Tray Extras Appropriate bone screw set; drill bits ; Gelpi , Langenbeck and small Hohmann retractors; small pointed reduction forceps; chuck; K-w ires; pin/wire cutters.

Surgical Approach Craniolateral approach as described in Operati ve Technique 18. 1. Reduction and fixation Skeletally mature dogs Assess the state of the femoral head and neck. In more chronic cases, damage due to abnormal rubbin g of bone and cartilage may dictate an excision arthroplasty or hip replacement. Rotate the femoral neck out laterally and support it with Hohmann retractors (Figures 18.5 and 18.6). Drill the gliding hole for the lag screw retrograde from the neck to the subtrochanteric area (Figure Hohmann 18.6). (An alternative method is to drill the hole fro m lateral Drill bit retractor to medial, usi ng a C-shaped dri ll guide with the point of the guide centred on the lateralized femoral neck and the drill positioned over the third trochanter.) Reduce the fracture using small reduction forceps from fovea to greater trochanter after rotating the fragment into place with the aid of a small Hollmann retractor. A pair of small reduction forceps applied to the greater trochanter is also a useful aid in reduction as it allows easier mobilization of the bone. It isa lso possible to hold the fracture reduced by pressure against the acetabulum. Drill the thread hole for the lag screw using a Femur rotated to centring insert sleeve through the gliding hole (Chapter 9). lateralise femoral neck Before this hole is drilled, measure the depth of the fragment Figure 18.6: Retrograde drilling a/the glide hole from the X-ray, add this to the depth of the gliding hole and ill the Lag screw fixat ion 0/fe morall1eckfracltires. set an adjustable stop on the drill bit to the required length. A Hohmann retractor thin piece of plastic tube which can be slid into place on the drill bit will suffice. This avoids penetration of the articular cartilage. An alternative is to set the drill bit in the dri ll to the Kirschner wire measured total length of the gliding and thread holes. When measuring for screw size, do not add 2 nun to the screw length as is done with cortical bone. If a partially threaded cancellous bone screw is used, a gliding hole is unnecessary but careful measurement is needed to ensure that the screw threads are all within the fragment. Tap the hole. When the lag screw has been inserted, an anti-rotation K-wire of s imilar

length, or slightly less, is inserted parallel to the screw, using a chuck or power dri ver (Figure 18.7). Bend over the K-wire, with the chuck attached well away from tile bone, and cut it short so that the bend prevents medial migration of the wire. An alternative technique is the use of three K-wires (helow).

•

Figure 18. 7: Femoral lJeckfracture repaired with a lag screw alld a mi-rOTational K-wire. Pointed reductionforceps can be Ilsed to maintain redu ction oj ajemoral Ileck!racwre jollowing the drilling ojthe screw glide hoLe (see text jar detaiLs) .

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Physeal, su bcapital and intertrochanteric fractures

Cats and skeletally immature dogs Two or three K-wires are used. The pins are placed retrograde from the fracture surface. Following reduction of the fracture, they are inserted the measured distance into the epiphysis before being cut (Figure IS.S). It is also possible to insert the K-wires normograde after reducing the fracture but this involves more guesswork in optimally positioning the pins.

Figure 18.8: Femorai neckj'racture repaired with three K-wires.

Allemative Technique Use a trochanteric osteotomy approach. After reducing the fracture, hold it reduced by pressure aga inst the acetabulum. Then insert two orthree K-wires from the margins of the epiphysis into the femora l neck in a cruciate pattern and punch them below the articular surface using a hammer and small flatended pin (Figure IS.9).

Figure 18.9: Repairo/aproximal/e moralphysealfracture in a dog using collntersunk K-wires insertedfrom the articular margin (a trochanteric osteotomy was repaired with a Jag screw). This is an alternative technique for the repair 0/ physea/ and neek/ractures (see text/or details).

Closure See Operati ve Technique IS. 1. Post-operative Care See Operative Technique IS. 1.

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Fracture of the greater trochanter ,

Positioning Lateral recumbency with affected leg uppermost. Assistant Optional.

Tray Extras Gelpi self-retaining retractors; chuck; K-wires; pin/w ire cutters; wire for tension-band; drill and bit; pointed reduction forceps; pliers/wire twisters. Surgical Approach Incision is made over the greater trochanter directly on to the fracture. RelilictiOIl and Fixation The fracture is reduced by grasping the trochanter with small reduction forceps and pulling it, complete with its gluteal muscle insertions, back into position. Two K-wires are then inserted diagonally from lateral to medial through the trochanter and across the proximal femur, angled about 50 0 distall y (see Figure 17.1 7). The tension-band wire should not be applied in a skeletall y immature animal as it wi ll close the growth plate.

Alternative tech1lique It is also possible to use a lag screw for this fixation in mature animals. The screw is inserted at an angle of 50 0 towards the medial cortex (Figure 18.9).

Post-operative Care See Operati ve Teclmique 18.1.

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Intramedullary pinning

Pre-operative Planning The pin length is measured from the dista l end of the medull ary canal to the top of the greater trochanter. In a fat animal, an extra allowance for the depth of soft tissues above the trochanter has to be made. Pin size may also be assessed us ing a radiograph of the contralateral femur. The author prefers to pre-cut the pin to length and round off one end to make that end as atraum atic as possible; this end will be exposed to soft tissues and is less li kely to cause irritation. The pin should be slightl y narrower than the narrowest part of the medullary canal. Positioning Lateral recum bency with affected leg uppermost. Assistant Optional.

Tray Extras Chuck; bone holding forceps; appropriate s ize intramedulla ry pin; wire for cerclage; pliers/wire twisters; pin/ wire cutters; large pin cutters; drill and bits; Gelpi self-retaining retractors; +/- appropriate external fixator kit if type I fixator to be used as adjunct.

Surgical Approach Make a s kin incision over the cranial border of th e bone from th e subtroc hanteric area to the femoral condyles. Retract the skin and make a small incis ion in the fascia lata in the same line w here it is thi ckest, to find the muscle divis ion between the biceps femoris caudally and the vastus latera lis cranially. The incision should lead into the gap between the two muscles. If th e gap is not found , the incis ion is usually too ca udal. Once found, extend the fascial incision with scissors and retract the biceps ca udally to expose the shaft of the bone (Figure 18.10). The vastus has loose attachments to th e femoral shaft which must be cut to allow its cranial retraction. The adductor muscle has firm attachments to the caudal border of the bone which include part of the femoral blood suppl y: these attachments sho uld be disturbed as little as poss ible. This exposure allows access from the subtrochanteri c area to the condyles. Should access to th e greater troch anter be necessary, the insertion of the s uperfi cial gluteal muscle may need to be tenotomized and the origin of the vastus muscle on the third trochanter has to be incised and reflected subperiosteall y and distall y to ex pose the trochanter.

Biceps femoris

m. Vastus lateralis

Adductor magn us

m.1"lr--cfIL---L Tensor fasciae lata m.

~~~~l-1-tr-rT Tearing ~ of muscle

Femoral shah

Gelpi retractors

Figure 18.10: Lateral exposure of a femoral diaphyseaL fracture.

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Intl'amedullary pinning

Reduction alld Fixation Examine the fracture ends to ensure that there are no fi ss ure lines running longitudinall y. If there are. it is essential to place cerclage wires around them before proceeding further to avoid the ris k of spl itting the bone durin g fracture reduction. PRACTICAL TIP It is easier to insert the pin retrograde from the fracture site up the proximal segment.

WARNING This must be done with the hip in extension to avoid damage· to the sciatic nerve.

PRACTICAL TIP When using the larger pins, it is easier to drill a pilot hole with a narrower and sharper pin first. The pin is dri lled up the medullary canal until the point is fe lt to penetrate the trochanteri c fossa, withdrawn and reversed to pass the blunt end up until il tents up the skin over the trochanteric fossa . Make a small incis ion over the head of the pin and re·attach the chuck to it. Withdraw the pin proximall y to leave I cm protruding from the prox imal fragment at the fracture site. Angle the fragments laterally (bone holding fo rceps may be required on the distal fragment) and hook the distal fragment on to the point of the pin (Figure l S. lla). Flatten down the fracture and dri ve the pin down the requisite distance (Figure I S. llb). When the chuck is removed, the pin should be at or just above the level of the trochanter and lying under the skin without tenting it up.

Jacobs chuck & pin

Pin nearly impacts

medullary ]

PRACTICAL TIP Alignment of the edge of the adductor muscle on the caudal border ofthe femoral shaft is a useful check for correct alignment.

PRACTICAL TIP If the canal is too wide for the largest pin (curTently 6.25 mm), use two or three smaller pins to 'stack' the canal (C hapter 9). However, a better alternative is plate and screws (Operative Technique 18.5).

•

Fiss ure line

canal at narrowest point

Figure 18.11: (aJ Reducingfracluredfemur usillg illltameduflary pill. Note cerc:lage wire pre-placed around afissllre line. (b) Fractured/emur reduced lVilll illt,:ameduJlary p ill.

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Intramedullary pinning

P,-eventing rotational insta bility in tra nsverse a nd s hort oblique fr actu res If there is rotati onal instability, a two- pin extern al fi xa tor should be applied with the prox ima l pin in the subtroc hanteri c area and the distal in the lateral condyle, joined by a single connectin g bar (Chapter 9) (Figure 18.12). An alternati ve in short oblique fractures is to use hem i-cerclage wire which has been pre-placed by drill ing a hole through both corti ces of one fragment and then tightened around the other after pin placement.

Figure 18.12: COllllllilllltedfracruredfemur ill a cat repaired with WI illtramedullary pill, three cerclage wires alld all antirotatioll, tlVO pill external fixator

Clos"re The wo und is closed by a contin uous suture of absorbable suture in the fasc ia lata; thereafter closure is ro utine. If a wider approach has been made proximally, the ori gin of the vastus is sutured to the gluteal tendon inserti ons on the greatertrochanter and the superfi cial gluteal is re-attached to its tendon with mattress sutures of PD S or VicryL Post-operative Care Dogs: lead exercise only for 6 weeks. Phased return to acti vity_ Cats (a nd sma ll dogs): room confinement; cage confinement in some cases.

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Bone plating

Pre-operative Planning Plates may be positioned from the distal femoral condyles to the top of the greater trochanter. Plates are appli ed to the lateral surface of the femur, which is the tension side. As a plate is positioned more proximally and distally, it has to be contoured more to allow for the bone curvature. Positioning Lateral recumbency with affected leg uppermost.

Assistant Useful. Essential for some fractures (see below). Tray Extras Appropriate size bone screw set; drill and bits; Gelpi self-retaining retractors; +J- orthopaedic wire; +Jdistract or; bone holding forceps; small pointed reduction forceps; Hohmann retractors; curette for bone graft. Sltl'gicai Approach As for Operative Technique 18.4. Redltction and Fixation Oblique and spiral fractures are difficult to reduce. Assistants are essential to aid in traction on the limb and the use of several pairs of bone holding forceps is usually necessary to apply the traction and rotation manoeuvres needed to reduce the fractures. Use a distractor. Avoid glove puncture on sharp spikes of bone. Where comminution involves the subtrochanteric area, it will be necessary to contour the plate to the top of the greater trochanter with probably two short screws angled distaUy through the plate and into the trochanter. (The useof a dynamic compression plate is recommended as its oval holes allow easier positioning of oblique screws.) In addition, a longer screw passulg through the plate and along the femoral neck from the third trochanter area is needed (Figure 18.13). Where an intertrochanteric fracture is also present, the screw along the femoral neck has to be a lag screw. This can be supplemented by an anti-rotation K-wire, which is inserted first to hold the fracture after its reduction and before the lag screw is inserted. It is also possible to use hook plates in this situation, but this requires some special instruments and they are not widely used in small animals.

Figure 18.13: Subtrochanteric comminuted fracture of jemur repaired using fag screws alld llellTralizafioll plate.

Closltl'e As for Operative Teclutique 18.4. Post-operative Care As for Operative Technique 18.4 .

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OPERATIVE TECHNIQUE 18.6 VetBooks.ir

External fixation

Positioning Lateral recumbency with affected leg uppermost. Assistant Optional.

Tray Extras Appropriate size external fixator set; bone holding forceps; Gelpi self-retaining retractor; chuck/drill ; large pin cutters. Surgical Approach When a fixator is used as the sole means of fracture stabilization (Figure 18.14), the pins can be inserted through stab incisions following closed reduction of the fracture. Alternatively a limited lateral approach is used (Operative Technique 18.4). Refer to the concept of a minimally invasive strategy for fracture repair discussed in Chapter 10.

Figure /8.14: Severely cOlI/mintlfed femoral diaphyseal fracture in a cat. The fracture was stabilized /Ising a lIlIilateral Illliplallar external skeletal jixClror alld healed uneventfully.

Post-operative Care See Chapter 9.

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OPERATIVE TECHNIQUE 18.7 VetBooks.ir

Fractures involving the distal femoral growth plate

p,.e-operative Pla1lliing Rush pins may be purchased ready made, but most are too thick. It is easy to make you r own from K-wires with the help of a vice and a triangular file (Figure 18.15). For cats, 1.0- 1.5 mm diameter pins are used; and for dogs, 1.5- 2.0 mm. The length, measured from a pre-operative radiograph, is a distance that will extend from the base of the condyle to approximately one-third to one-half the length of the diaphysis. Cut to make hook

(a)

Kirschner wi re bent over

(b)

Hook end

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PARTFOUR - - - - - - - - - - - - - - -

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Complications of Fracture Management

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CHAPTER TWENTY THREE

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Fracture Disease John F. Ferguson

INTRODUCTION Fracture disease is the term used to desc ribe the complication where a limb remains with no function, or suboptimal function, after treatment of fractures. The phrase was used by Muller (1963) to describe the syndrome of muscle atrophy or cont racture, joint stiffness and osteoporosis resulting from prolonged immobi lization of a limb. Functional disability may persist long after the fracture has healed. Complications arising as a consequence of prolonged periods of limb immobilization stimulated the formation of the AOIASIF group. This group developed instruments and implants to facilitate accurate fracture reduction and stabilization, which ensures earl y limb use so that controlled ambulation can be encouraged in the earl y post-operati ve period, reduc-

development of joint sti ffness. Immobilization of the stifle joint fo rthree weeks with and without concurrent muscle trauma in growing dogs did not lead to a permanent reduction in range of joint motion (Shires et at., 1982) . However, immobilization of distal femoral fractures treated by external splintage resulted in a stiff stifle joint after a period of 3-7 weeks. The e lbow and stifle joints appear most susceptible to post-traumatic stiffness. The number of joints that a muscle group crosses affects its tendency to atrophy by virtue of the extent of immobili zation the muscle group experiences. With elbow inunobili zation, for

ing the chance of fracture disease occurring.

AETIOLOGY Immobilization of a limb can lead to many stmctural, biomechanica l, biochemical and metabolic changes in the affected tissues. It is well known that bone in an immobilized limb undergoes atrophy. The fact that other limb tissues - including muscles, ligaments, articular cartilage and synovium - atrophy as well has probably received less recognition. This is an important consideration as changes in articular cartilage and joint capsule may be irreversible and progressive (Akeson el aI., 1987). Fracture disease usually occurs in association with surgical treatments and immobili zation methods that do not provide optimal stability or that limit or prevent earl y acti ve movement and limb use (Figure 23 .1a,b). Non-union, de layed union, osteomyelitis and improper treatment of articular fractures all predispose to fracture disease (Figures 23.2a,b and 23.3). Fractures close to joints cause reduced range of joint movement due to the healing resp·o nse and the development of adhesions in periarticular connective tissues. Fibrous adhesions between joint capsule, muscle, tendon and bone limit the normal sliding between these structures. Effects of muscle trau ma seem to playa limited ro le in the

Figure 23.1 : (a) A 2-year-old Jack Russell terrier, 2 weeks after surgical treatll/elll of a closed comminll1ed diphyseal tibialjraclIlre. Note the loss of.soft tissue around the jracIllre site. Two cerclage wires are visible. (b) Medio/ateral and craniocaudal radiographs o/tfle tibia ojthe same dog. Gross ill.stability at the fracture site lias resulted/rom the inappropriate use ojimplallts. A Robert Jones dressing had been applied post-operatively to help to 'stabilize' the jracture.

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in joint range of motion may be evident. Manipulation of the joints may elicit pain. Ligamentous laxity after prolonged support is common, especially in immature animals. Joint hyperextension at the time of cast removal in young dogs results in abnormal joint posture (Figure 23.4a) . This usually resolves as muscle tone returns fo llowing limb use and exercise. Animals with fracture disease after intra- or peri-articular fractures may have a severe or non-weightbearing lameness,

marked muscle atrophy and decreased or loss of joint range of motion. Radiography may reveal osteoporosis (Figure 23.4b). Animals with severe quadriceps muscle contracture show characteristic signs and this

condition will be discussed later in the chapter. Figure 23.2: (a) Craniocaudal radiograph a/a Saluki-cross with a lateraL humeral condylar fracture 8 weeks postoperatively. A lion-union has resulted due to/ailure to reduce thefracrure alld gain rigid stability. (b) The same dog, showing signs 0/ 'fracture disease' 0/ the right forelimb. Note the presence of severe muscle atrophy.

Figure 23.3: Post-operative lateral radiograph of the right elbow ofa 5 year-oLd Springer Spaniel. One o/rhe K-wires used to re-attach the olecranon is placed intra-articuiarly. The dog did /lot use the limb ulltil the K-wire was removed 3 weeks post-operatively.

example, the effect on the triceps brachii muscle is greater than that on the elbow flexors because the triceps is closer to being a 'one joint' muscle than the elbow flexors (Anderson, 1991). Immobilization of the limbs of animals during their rapid growth phase may have especially dramatic consequences on the entire limb. Fracture disease in the young animal may result in disturbances in the growth of bones, joint subluxation, bone hypoplasia and limb shortening (Bardet and Hohn, 1984). The atrophy of muscles, ligaments, articular cartilage and synovium is not caused by decreased blood flow. Richards and Schemitsh (1989) showed that blood flow to the affected limb actually increases during fracture healing and limb immobilization.

CLINICAL SIGNS The clinical signs of fracture disease depend on the duration and severity of the condition. Immediately after cast removal, mild muscle atrophy and reduction

Figure 23.4: (a) A 12-week-old Labrador's hindlimb after being ill a cast/or 3 weeks to treat a tibial fracture. Note the severe hyperextension of the digits due to laxity of the associated soft tisslles. The signs resolved 4 weeks later. (b) Dorsopalmar radiograph of the /001 of the same dog, showing osteoporosis o/the bones in the distal limb.

PATHOPHYSIOLOGY The effects of experimental immobilization on limb tissue has been studied in various species, including

the dog and cat. Changes in bones, muscles, articular cartilage, synovium, ligaments and other peri-articular structures have been demonstrated.

Muscle atrophy Elimination of normal weightbearing forces and muscle activity leads to flaccidity and atrophy of skeletal muscles within 3-5 days of inunobilization. This decrease in muscle size results in decreased muscle

strength. Braund et ai. (1986) found muscles composed of type I fibres ('slow' fibres) atrophy to a greater extent than muscles composed of type II fibres (,fast' fibres). Half of the total muscle mass lost during long-term immobilization occurs in the first 9 days (Booth, 1987). Anti-gravity muscles atrophy to a greater extent than their antagonists. Disuse muscle atrophy is generally reversible: unlike disuse osteoporosis, it appears that atrophic muscle maintains its regenerative

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Fracture Disease

capacity even after long periods of immobilization. However, the recovery period varies between two and four times the duration of the immobilization.

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Disuse osteoporosis Disuseosteoporosis is characterized by decreased bone mass resulting from muscular inacti vity and reduction in weight bearing. Osteoporosis after immobilization can be di vided into phases. Uhthoff and Ja worski (1978) examined limbs of Beagles that had been immobilized and found the bone mass responded in three stages : it declined rapidl y fo r the first 6 weeks but returned almost to control values during the following 8-12 weeks of immobilization; a second phase of slower but longer-lasting bone loss ended 24-32 weeks after immobilization; the third stage was characteri zed by maintenance ofthe bone mass by some 30- 50 % of original values. The distal limb bones lost more bone than the proximal limb bones. The initiating cause of disuse osteoporosis is not well understood. Lack of muscular acti vity, increased vascular supply to the affected limb and absence of weightbearing, wllich decreases the piezoelectric action of crystals on bone cells, are important factors in inducing bone atrophy. The production of new bone after immobilization occurs 10 times more slowly than bone removal. Also, there is evidence that osteoporosis in young dogs and in limbs immobilized longer than 12 weeks may not be totally reversible (Bardet, 1987).

Articular and periarticular changes Cartilage and menisci depend on synovial fluid for their nourishment and lubrication. Motion is important in producing circulation of synovial fluid and thus the flow of nutrients throughout the joint. Articular changes can occur within a few days of inunobilization and are more pronounced in joints that are not subject to intermittent load bearing (Jurvelin, 1986; Bardet, 1995). Substantial reduction in cartilage proteoglyca n synthesis and content with subsequent cartilage softening occurs. Intra-articular fibm-fatty connective tissue fo rms within a month of immobilization, and between 1 and 2 months adhesions can occur between this tissue and the underlying cartilage. With time, major cartilage alterations occur including fibrillati on, deep erosion and cleft fo rmation. Fibrous and sometimes cartilaginous or bony ankylosis between adjacent joint surfaces may take place. Biochemical and morphological changes are rarely irreversible before 4 weeks of immobilization, but after 7 weeks changes in articular cartilage may be permanent and even become progressive despite remobilization (Akeson et at., 1987). Mechanica l restriction in motion leads to peri-

307

w as less than w hen immobili zed in ex tens ion

(Ouzounian 1986). Thickening of the joint capsule occurs, due to fibrous hyperpl asia, and type B synoviocytes proliferate in the synovial lining. Stress deprivation weakens articular ligaments due to alterations in the glycosaminoglycan and collagen fibre relationship. Bone reabsorbtion in the cortex immediately beneath the ligament attachment site may lead to avulsion fractures (Noyes, 1977).

Growth disturbances Immobilization of limbs of growing animals may lead to severe growth disturbances in the entire limb. Immobilization of the stifle in dogs younger than 3 months of age can lead to hip subluxation, bone hypoplasia and increased femoral torsion. Hip subluxation is seen consistently after 8 weeks of cast application with the stifle fixed in an extended position (Bardet, 1987). Lac k of weightbearing leads to reduction in osteoblast acti vity and a resultant decreased physeal growth.

QUADRICEPS CONTRACTURE Quadriceps muscle contracture is a common complication of distal femoral fractures and is probably the commonest manifestation of fracture disease in the dog. Fractures treated by internal fixation, supplemented by extension splints, are more prone to developing this complication. The initiating factor appears to be fibrous adhesions tying down the vastus intermedius to the distal end ofthe femur with incorporation of the muscle into the organizing callus. This occurs most often and is likely to be most severe in young growing dogs.

Clinical signs There is rigid hyperextension of the affected limb with reduced flexion of both the hock and stifle joints. The quadriceps muscles are firm and atrophied (Figure 23. 5). Stifle hyperextension may be present to such a degree that it is bent backward, termed genu recurvatum

articular tissue contractures, the severity of which is

related to the duration of immobilization. The position in which the joint is immobili zed appears to be significant. When rabbit stifl es were immobilized in flexion, the incidence of osteoarthritis

Figure 23.5: A l-year-old Shetland Sheepdog showing signs of severe quadriceps muscle col1lraclllre. Hyperextension of both the stifle and hockjoillls is present. Supplied by M r C SI/!a(/.

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Prognosis

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The prognosis for a fu ll return to limb function is extremely poor and is guarded even for a return to reasonable function. Residual lameness is to be expected. Stifle arthrodesis or limb amputation may be necessary if there are advanced changes in the stifle or ifsevere hip subluxatio n or limb shortening is present.

CLINICAL CONSIDERATIONS IN AVOIDING FRACTURE DISEASE

Figure 23.6: MediolateraL radiograph of the left stifle joint of the dog ill Figure 23.5. The joillt is hyperexfended alld the patella is proximal to file trochlear groove. Sjjpplied by AIr C Slefld.

(Figure 23.6) . The patella is pulled proximally in the trochlear groove and may be luxated medially. In young dogs, subluxatio n of the hip with reduced internal and ex ternal rotati on and a positive Ortolani sign may be present.

Treatment If the changes are mild then a co nservative approach may be the best opti on. In moderate or severe cases s urgery may be indicated. The aim of s urgi cal treatment is to restore a functional range of motion to the stifle j o int by freeing adhesions between muscle groups and th e femur, breaking down the periarticular adhesions, lengthening the quadriceps muscle groups and regaining an angulation of the stifle joint to allow weightbea rin g. If the limb is severe ly short or if hip sublu xation and severe disuse osteoporos is are present then surg ica l treatment is co ntraindicated. Many su rg ical techniques ha ve been described for the treatment of quadriceps contracture and include partial quadri ceps myotomy (Leighton, 1981), Zmyoplasty (Bloomberg, 1993), freeing of adhesions an d implantation of plastic sheetin g between th e quadriceps and distal femur (Wright, 198 1), s liding myoplasty and quadriceps insertion re location (Bloomberg, 1993). Excision of the vastus intermed ius appears to be the single procedure most likely to be successful - but o nly in the ea rl y stages of the condition, before development of irreversible joint changes. Bardet (1987) gives a full account of the operative technique. Regardless of the s urgery performed, it is important to'maintain the stifle in flexion with eith~r a figure-of-eight dressing or external pin splintage for 4-7 days. Passive flex ion and extension is perfonned when the supports are removed. The use of a dynamic apparatus for the prevention of recurrence of quadriceps contracture has been described (Wilkens et aI., 1993).

The basic guideline of providing stable fi xation when treating fractures to fac ilitate ea rly return to limb function is critical to a satisfactory outcome and avoidance of fracture disease. In some circumstances immobili zation ofthe limb in a cast is the treatment of cho ice, although the clinician sho uld remember that fracture disease is a potential complication with this method. The duration of immobili zation should be only as long as necessary to achieve bony union, and the limb should be placed in a flexed position to enable the anima l to wa lk on the immobilized leg. When internal fixat ion is used, devices that lead to rapid return of limb function should be chosen. For example, dogs with transverse mid-diaph ysea l fractures of the femur stabilized w ith bone plates benefi ted from full function of the limb in an average of 3.5 weeks, compared wi th 7.5 weeks in dogs treated with intramedullary pins and half Kirsc hner splints. When intramedullary pins were used alone the time taken for normal limb function to be restored was 9.2 weeks (Braden and Brinker, 1973). Any delay in return of limb function wi ll increase th e chance of fracture disease developin g. The app li cation of Schroeder-Thomas splints (Figure 23.7) has a hi gh incidence of develo ping serious complications, including non-unions, malunion and fracture disease. In th e author's opinion, there is no place for the use of these devices in modern small animal vete rinary practice.

Figure 23.7: Photograph of a 6-month-old German Shepherd Dog with a Shroeder- Thomas extension splint applied to the hindlimb for the treatmel11 0/ a distal femoralfraclllre.

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When periarticularcontractures occur, activeexercise and physical therapy may be beneficial. In a study by Olson (1987),12 dogs had their carpi immobilized in a cast for 6 weeks. In the ensuing 4 weeks, after cast removal, half the dogs received daily passive physiotherapy while the others did not. The dogs were allowed to ambulate freely in their cages during this period. Dogs that had received physiotherapy had a statistically greater range of carpal joint motion than dogs that had not received physiotherapy. However, the mean range of motion difference between the two groups was sma ll (an average of 2°) . These results would suggest that physiotherapy may onl y have a small effect on joint stiffness and little effect over and above the mobilizing effect of ambulation. Swimming provides an excellent form of active, weight-supported exercise in the early rehabilitation period (Figure 23.8) . Goniometry (Figure 23 .9) is important if objective assessments for response to treatment are to be made.

Figure 23.9: Use of a goniometer to measure the range of movement of the stifle joint after treatment of a supracondylar femoral fractu re.

Figure 23.8: Swimming ill a bath tub provides excellel1t weight-supported exercise and physiotherapy in the early post-operative period.

Manipulation of chronic stiff joints under anaesthesia can sometimes be used to restore normal motion by tearing adhesions and other soft tissues. Generally, however, this technique is discouraged by most physiotherapists and in fact forceful stretching techniques that cause tearing of tissues can promote further scar formation and increase joint stiffness (Herbert, 1993). Furthermore, manual stretching of adhesions is often contra-indicated because this technique usuall y exacerbates the severity of the mature contracture. A stretch reflex may be stimulated which is painful, causes further muscle contraction and has few long-term beneficial effects. An alternative, more useful technique when dealing with contractures is activation or strengthening of the weak opponent muscle. In veterinary medicine,

this can only realistically be achieved by active exercise - either weightbearing or swimming. Cooling by applying ice loca lly to decrease nerve conduction velocity and thus myotactic reflex activity may increase inhibition ofthe contracted muscle immediately before exercise periods. Passive lengthening using splints is used in humans to produce increasing but gentle prolonged stretch of contracted muscles and induces less reflex stimulation than periods of rapid muscle stretching. Non-steroidal anti-inflammatory drugs (NSAIDs) appear to ha ve little effect on posttraumatic joint stiffness but have been shown to reduce joint swelling after trauma (More et aI., 1989).The analgesic effect of NSAIDs has an important role in encouraging return to weightbearing and limb function in the early post-operative period. Experimentally, joints immobilized for 4 weeks and then treated with four weekly intra-articular hyaluronic acid injections showed reduced cartilage proteoglycan loss and reduced joint stiffness, and superficial cartilage damage was prevented (Keller et al., 1994). Dexamethasone (1 mg/kg) has been shown to decrease joint stiffness after trauma although no statistically significant effect on joint swelling was seen (Grauer et aI., 1989). The corticosteroid effect of reducing inflammatory mediators and decreasing

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collagen production and cross-linking is li kely to be res pon s ible . The use of hya luronic acid and corticosteroids has not been full y evaluated in canine fracture disease and so is not currently advocated for lise in clinical practice

SUMMARY Fracture disease is most commonl y encountered with externa l coaptation ofa limb by using a cast. However, the changes occur to a lesser extent with other means of fixation. The clinician should adhere to the principles of fracture repair and make every attempt to avoid fracture disease, since no satisfactory treatment exists. Stable fixation of fra ctures that a llows the limb the most rapid return to functional weightbearing without immobili zation should be employed. If a cast is used, the limb should be fi xed in a walking position. Severe manifestations of fracture disease can be avoided with proper fracture management.

REFERENCES Akeson D, A mici D and Abel MF ( 1987) Effects of immobilization on joints. Clinical Orthopaedics alld Related Research 219, 28-37. Anderson OJ ( 199 1) Fracture di sease and rclatcd contracturcs. VeteriI/ary Clillics of North America 21 , 845 -858. Bardet JF ( 1987) Quadriceps contracturc and fracturc discase. VeterilIary Clinics of North America 17, 957-993. Bardet JF ( 1995) Fracture disease. In: Small Allimal Orthopaedics, ed . M Olmstead, pp. 3 19-329. Mosby-Year Book Inc., Missouri. Bardet JF and Hohn RB ( 1984) Sublu xat ion of the hip joint and bone hypoplasia associated with quadriceps contracture in young dogs. Journ al ofAmericall Veterinary Medical Associatioll20, 42 1- 428. Bloomberg M (1993) Muscles and tendons. In: Textbook of Small Anil/wt Slirgery 2nd edn, cd. S Slattcr, pp. 20 I0- 20 II . WB Saundcrs & Co. , Philadel phia. Booth FW ( 1987) Phys iolog ic and biochemica l effects of immobilization on musclc. Clinical OrlllOpaedics ([nd Rela/ed Research 219, 15-20. Braden TD and Brinkcr \VO (1973) Effcct of certain fi xat ion devices on

functional limb usagc in dogs. Journal oflhe American Velerillary Medical Association 162,642-646. Braund KJ, Shircs PK and Mikeal RL ( 1986) Type I fibre atrophy in the vast us latera lis in dogs with femoral fractures treatcd by hyperextcns ion. Velerillary Palhology 17, 166-177. Graue r JD, Kabo 1M , Dorey FJ and Meals RA ( 1989) The cffcc ts of dcxamethasonc on pcriarticular swclling and joint sti ffness fo llowing fracturc in a rabbit model. Clil1ical Orlhopaedics and Related Research 242, 277-284. Herbert R ( 1993) Prevcnting and trcati ng stiff joi lils. In: Key Issues ill MI/sclltoskeleral Physiotherapy, cd. J Crosbie and J MacConncl , pp. 114-141. BUl1crworth-Hci nmann , Oxford. Jurvelin J ( 1986) Softening of canine arti cular cartilage aftcr immobi lization of the knce joint. Clinical Orlhopaedics alld Related Research 207, 246-250. KellcrGW, Aron DA, Row land GN, Odcnd ' hal S and Brown J (1994) The effect of trans-stine extemal s keletal fixation and hya luronic acid the rapy on ll rticu lar cartilagc in the dog. Velerinary Surgery 23, 11 9- 128. Leighton RL ( 1981 ) Muscle contractu res in the limbs of dogs and cats. Velerillary Surgery 10, 132. More RC, Kody MH, Kabo JM, Dorey FJ and Mea ls RA ( 1989) The cffects of two non-steroidal anti -inflammatory drugs on li mb swell ing, joint stiffness, and bonc torsional strcngth followin g fracture in a rabbit model. Clinical Orthopaedics alld Rela/ed Research 247, 306-311. Muller ME (1963) Intcmal fixation for fres h fractu res and for nonunioll . Proceedillgs oflhe Royal Society of Medicine 56, 455 -460. Noyes FR (1977) Functi ona l propert ies of kncc ligamcnts and alte rations induced by immobilization. Clinical Orlhopaedics alld ReIa/ed Research 123, 210-42. O lson VL (1987) Eval uation of joint mobilization treatments. Physical Therapy 67, 351-356. Ouzounian TJ ( 1986) Thc effcct of pressllrisation on fractu rc swell ing and joint stiffness in the rabbit hind limb. Clinical Orthopaedics alld Related Research 210, 252-257. Richards RR and Schemits h EH ( 1989) The effect of na p coverage on bone and soft tissue on blood fl ow fo llowing devascu1arisalioll of a segment of tibia. An cxperi mcntal in vestigation in the clog. JOllfllal ofOrtlwpaedic Research 7,550- 558. Shires PK , Braund KG , Milton JL and Lui W (1982) Effect of localised trauma and tempora ry splinting on immature s keletal muscle and mobility oflhc fcmorotibial joi nt in the dog. American JOl/ fllal of Velerillary Research 3, 454-60. Uhthoff HK and Jaworski ZFG ( 1978) Bone loss in response to long term immobilization. Journal of BOlle and Joilll Surgery 608, 420429. Wil kens BE, McDonald DE and Hulse DA (1993) Uti lization of a dynamic stifle fl exion apparatus in preventing recurrence of quadri ceps contracture: a cl inical report. Veterillary Comparative OrIhopaedics and Traumatology 6, 2 19-223 . Wright RJ (1980) Corrccti on of quadriccps contracturcs. California Veterillariall l ,7- 10.

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Implant Failure Malcolm G. Ness

Most fa ilures in orthopaedics can be placed at the feet of the surgeo n D. L Piermattei

If a bone is subjected to moderately increased stress be it from increased activity, patient weight gain, biomechanical alterations or other reasons - the bone will undergo reacti ve hyperplasia. This process is described by Wolff's Law. Following fracture surgery the metal implants used in fracture repa ir must bear all or part of the load usuall y carri ed by the bone. Without bone's capacity for reacti ve hyperplasia, overloaded metal implants may fatigue and fail. Is occasional implant failure an inevitab le complication of fracture surgery or can it be avoided? The purpose of this chapter is to look more closely at how and why im plants fa il in the hope that an increased understanding of the relevant bio logica l, biomechanical, mechan ica l and metall urgic phenomena can be usefully applied to the benefit of patients. Fracture repair by open reduction and internal fixation has been described as a race between bone healing and implant fa ilure. Whilst such biomechanical brinkmanship cannot be condoned two points are well made: metallic implants calIDot be expected to function indefinitely and biological facto rs such as patient age, disease status, surgical technique, etc. can greatly influence the fate of bone healing. This review of implant fai lure in small animal fracture surgery will be divided into three subsections:

I. The properties of 316L stainless steel - the material from which almost all veteri nary orthopaedic implants are made (Chapter 8). 2. Mechanics of material failure with reference to 3 16L stainless steel. 3. Modes of fa ilure of metallic orthopaedic implants ill vivo.

316L STAINLESS STEEL Almost all implants currently used in small animal fracture are manufactured from 3 16L stainless steel

(316L) . Although titanium alloy plates and screws are widely used in human orthopaedics, they perform onl y marginally better, yet are significantly more expens ive, than 3 16L stainless steel implants and so they have not found favo ur in veterinary orthopaedics. 3 16L is an alloy of iro n (55-60%), c11romium (17-20%), nickel (10-14 %), molybdenum (2-4%) and traces of other elements, notably carbon. Carbon content is kept below 0.03 % - the 'L' of3 16L stands for ' low carbon ' . This particular alloy has been developed from earlier materials - the addition of molybdenum and chromium to the recipe has enhanced the corros ion resistance of today's implants when compared with those in use in the 1920s. Despite these improvements, 3 16L, when perfectly clean, is remarkabl y reactive and therefore prone to corrosion. In practice this reactivity is beneficial , as it leads to the formation of a tightly bound oxide fi lm which covers the entire surface of the metal, and provides significant protection against furth er corros ion of the implant in vivo. However, corros ion res istance of3 16L stainless implants remains marginal and some corrosion is inevitable in most fractures where a plate and screws are used. T he amount of corrosion will not usually be enough in itself to be obviously significant, but may act in concert with stress concentration and metal fatigu e phenomena to cause ultimate fa ilure of implants. 316L is a relatively strong material, being able to withstand forces in the region of7 x 10' Newtons/m' in compression and the same under tension. This compares with cortical bone, Wllich can withstand forces of about 1.5 x 10' Newtons/m' in compression but rather less under tension - bone, unlike 316L, is anisotropic. A fuller description of the materi al properties of bone can be found in Chapter 3. Many of the mechanical principles governing the way in which bone fractures can equally be app lied to fracture of 3 16L, though obviously the forces requ ired and amounts of energy in volved are very much greater. T his inherent strength of 3 16L allows plates, pins, etc. to be made sufficiently small to allow implantation, whi le remaining strong enough to resist the biomechanical forces acting tllfough the implantbone composite during fracture healing.

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The mech anical properti es and corrosion resist-

ance of 316L can vary greatl y, depending on how an implant is made fro m the stock metal. For example, 316L implants made by casting rather than forging VetBooks.ir

have poor corrosion resistance and arc relati vely wea k,

being only marginallystrongerthan cortical bone. This observation need not trouble the surgeon, because almost all im plants used in veterinary fracture surgery are forged.

In conclusion, 316L can be forged and worked to form a variety of useful orthopaedic im plants. It is nontoxic, biochemica ll y inert, and strong enough and sti ff

which will be advanced, perhaps by only a fraction of a micron, each time the stress is re-a pplied. These experimentally applied cyclical stresses are not dissimilar to those applied to an orthopaedic implant duri ng normal weightbearing acti vity. The fatigue characteristics for a metal can be determined experimentally and desc ribed graphicall y (Figure 24.1). From this, weca n see that larger stresses will lead to earlier fati gue fa ilure and also that there is a level of stress below which fatigue failure will not occur - the fati gue limit. 500

enough to resist th e stresses normall y encountered in

small animal orthopaedics although, like many metals, it is prone to fatigue fa ilure and its corros ion resistance

is onl y just adequate.

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IMPLANT MATERIAL FAILURE A detailed account of the mechanicsof 3 16L is beyond the scope of tilis chapter, but it is interesting to compare the acute material failure occasionall y seen in implants with the material fa ilure of cortical bone during fracture, a process that has been described in some detail in Chapter 3. Similarl y, the concepts of stress concentration and fatigue failure are important to the understanding of how and why an implant might fa il and will be discussed in some detail. Early ac ute material failure of a metal implant is analogous to the material failure seen in bone as it fractures and is ex tremely uncommon in sm all animal

orthopaedics. Such sudden and catastrophic failure of a metal implies the development and propagation of a crack in the material. When compared with fracturing

300

Fatigue Limit

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200

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100

, • Number of cycles

Figure 24.1: Curve for stress versus /lumber of cycles, determined experimentally for 1045 carbon steel. The fatigue lilllit is a level of stress thaI wilL never cause material failure, IIO IIIOlIer how often the stress is applied The curve also sholVs that even quite modest increases in stress amplitude call greatly reduce the /lumber of cycies to failure: a 50% increase ill stress mighT reduce the life of tile material by a factor of 10 or //lore. Mu ch larger stresses - higher thall those recorded 011 this curve - will lead to permanent (plastic) deformation or even fracture of the material. (Redrawn/rom Radin el al. , 1992.)

bone, massive amounts of energy are required to propa-

gate a crack in metal as strong as 316L stainless steel; consequently this type offailure is rarely seen in small animal orthopaedics, where the necessary energy and force cannot be generated. Contrast this with the fail ures sometimes seen in equine long bone fracture

repair, when plates fracture as the patient attempts to rise following surgery. The considerable stresses generated in the plate by the uncoordinated efforts of the horse to stand are sufficient to initiate a crack in the implant, and the availability of large amounts of energy related to muscle strength and body mass a llows propagation of the crack and causes ac ute material fa ilure of the implant. In small animal orthopaedics, im plant fa ilure typically occurs some weeks after an apparentl y successful fracture repair. The concepts of metal fatigue and fatigue failure help to explain these cases. Stresses well below those needed to fracture an implant ha ve the potential to alter the implant material permanentl y. It has been shown experimentally that cyclical stresses applied to a metal, whilst not enough to fracture the material, will cause microscopic cracks

In practice, this ra ises the possibility of an im plant with infinite life ex pectancy, though in reality such an implant might be unacceptably large and un wieldy. Similarly, an implant subjected to sufficientl y large cyclical stresses will have a reduced life ex pectancy, and as the stress is increased the lifespan of the implant will be shortened. This infor mation can be used by the surgeon to select suitably strong implants which will not be prone to fatigue failure before bony union is acllieved. Equally the surgeon can consider restricting the patient's activity in an attempt to maximize implant longevity. In practice, the extentto which we can va ry implant size or levels of patient activity are limited and will have a relatively small effect on implant stress levels and implant longevity. Of more significance in this respect is the effect of stress concentrat ion, which has the potential to increase local stresses by several orders of magnitude, significantly reducing the time (number of cycles) to fa ilure. If a tensile force is applied to a metal bar, the stresses will be spread equally across the bar (Figure 24.2). If a hole or notch is cut into the bar, the same

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Implant Failure 313 stresses will be distributed less evenly and areas of stress concentration will arise (Figure 24.3). Areas

MODES OF FAILURE OF METALLIC IMPLANTS

where stress concentration occurs are known as stress

ri sers. VetBooks.ir

The similarities between these hypothetical models and some of our implants are obvious and the

importance of this stress concentration effect shou ld not be underesti mated: sharp, deep defects in a metal bar can result in local stresses being increased 1000 times or more. Most plates and wires in sma ll animal orthopaedics are placed on the tension aspect of long bones and are therefore subjected mainly to tensile stresses. Simi larl y, repeated bending stresses, which are a frequent precursor to implant failure, can be considered as cyclical tensile stresses applied to the convex surface of the implant, wi th the largest tensile stresses being recorded at the abaxial surface of the impl ant. Applying this information to the example of a bone plate on the lateral (tension) surface of a dog's femuT, we can apprecia te that the tensile stresses on the outer aspect of the plate will be exaggerated and that the screw holes will further enhance the stress concentrati on. Consequently, some of the metal making up the plate will be subjected to stresses many times greater than could be expected if onl y the patient's weight and the cross-sectional area of the plate were taken into consideration. The concept of stress concentration is essential to the understanding of why implants of seemingly reasonable size can fail.

• • Figure 24.2: When a metal bar is placed under tensioll, rile stress (shown here by lines offorce) is spread evenly across the bar.

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•

Having considered in some detail , but in isolation, the failure of a meta l subjected to simple mechani cal forces (material failure), we must now relate tltis to the clinica l situation (implant failure). Two major differences ex ist between the hypothetical models of material failure previously discussed and the failed implants encountered in small animal orthopaedic practice: All orthopaedic implants are fi xed to bone and so, from a mechanical viewpoint, they are part of a bone-metal composite and the size and distribution of stresses through the implant will be enormously influenced by its relationship to the bone. Orthopaedic implants are continually bathed in extracellular fluid which, being ionic and oxygen rich, is potentially corrosive. We can propose five distinct mechanisms that may cause, or at least contribute to, the failure of a metallic implant: Material fa ilure due to metallurgic imperfections or manufacturing fa ults Acute overload Electrochemical corrosion Oxidation-reduction corrosion ('crevice corrosion .) Fatigue failure . It is not unusual for several of these processes to be acti ng concurrentl y, and there exists potential for a destructi ve synergism that can easily be exacerbated by teelmical errors, such as inadequate fracture reduction, damage and marking of implants, poor tissue handling causing delayed union, etc.

Failure due to metallurgic imperfections or manufacturing faults 3 16L is a relati vely simple material to manufact ure. The meta l is extensively worked, forged and polished before being delivered as a fini shed implant and so the potential for an implant made from imperfect material getting as fa r as the surgeon is small. Impl ant fai lure due to metallurgic imperfection is corresponding ly rare.

Acute overload of implant Figure 24.3: Wilh the bar under tension, the number of Jines offorce at allY cross-section must remain constant. Cutting a hole or lIotch info the bar will lead 10 cOllcelllra tiol1s 0/ stress around the hole or at the extremity o/the lIotCIi. The similarities between these hypothetical models and our bone plates and screws are obvious.

Acute material failure of an implant (as distinct from fatigue fa ilure) is not common in small animal orthopaedics. Such fracture implies the development and then (importantly) the rapid propagation of a crack in the implant material, a process that requires larger amounts of energy than are generally available in small animal fractures.

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314

Manu al of Small Ani mal Fracture Repair and Management

One example of ac ute implant failure whi ch may be encountered is that of a screw head shearing o ff as th e screw is overtightened. A screw is a simple machine that converts a small torque into a much larger axial fo rce. During inserti on, the screw head becomes restrained aga inst cortex or bone plate. Further torque merely increases tens ile fo rce in th e shaft of th e screw. Applying knowledge of stress concentration phenomena we can predi ct a stress riser where th e thread cuts into th e screw shaft prox imall y, so that overti ghtening ca uses the sc rew head to snap off. Whilst tllis is certainl y an example of acute materi al fa ilure, the event is perhaps best viewed as techni cal error - it was not that the screw was too wea k but that the surgeon was too strong.

elemental iron into solution under conditions o f low oxygen tension and is mani fest as corrosion of the metallic implant. In practice, this type of corrosion occ urs quite frequently - usuall y between screw heads and plates or between a plate and corti cal bone; hence the descripti on 'crevice corrosion' . A lthough unlikely to res ult in extens ive damage to im plants, the importance of crevice corrosion is its action in potentiating other forms of implant degeneration. For example, crevice corrosion breaches the protecti ve oxide film present on all 3 16L implants, exposing them to furth er corrosive attac k. Additionally, the pits on the implant surface caused by crevice corrosion will act as stress risers, acceleratin g fati gue failure.

E lectrochemical corrosion T he principle of the electrica l storage battery is familiar to anyone who has studied elementary science. The key chemical reaction is that of a more active metal displacing a less acti ve metal fro m solution. For exampie, if we have two implants made o f di fferent alloys bathed in a solutio n (extracellular fluid) th en we can ex pect the more reacti ve metals to displace the less reactive fro m solutio n. The net result of this chemistry is loss of substance, and therefore strength, fro m th e implant - i.e. corrosion. The orthopaedi c surgeon must be awa re that implants of d iffe rin g composition should never be mi xed. Because almost all s mall animal orthopaedi c implants are made fro m 3 16L, electroc hemical co rrosion is an uncommon occurrence in our pati ents. However, inadvertent use of titanium plates with 3 16L screws or the use of no n-standard drill bits which may snap and be left ill situ are scenari os that may lead to electrochenlical corrosion. Corrosion products ca use pain, inflammati on and bone necrosis and in pract ice th e surgeon will recogni ze these caSeS primaril y as painful de layed unions, befo re s igni ficant im plant erosion or failure occurs.

Fatigue failure This is by far the most important mode of implant failure encountered in small animal orthopaedics. Typically, th e patient w ill have shown an earl y return to fun cti on and will have seemed to be we ll until th e implant 'suddenl y' breaks some weeks after surgery. Fatigue fa ilure occurs after an implant has been exposed to repeated cyclical stresses whi ch, though not large enough to ca use acute material fa ilure, will cause a small , permanent alterati on to the stru cture of th e metal. T he size of this microscopic defect will be proporti onal to the applied load and s imilarly the time to fa ilure of the implant will be in versely proportio nal to the applied load.

O xidation-reduction corros ion ( ' c.·e v ice corros ion ' ) The above description of electrochemical corrosion explained how metals of diffe ring reacti vity placed in solution g ive rise to an electri c current at th e expense o f loss of the more reacti ve metal in solution. Similarl y, identica l metals in environm ents with differin g oxidati on- reducti on (redox) potentials will display different levels of reacti vi ty and consequently ca n become in volved in electrochemical reacti ons comparable with those descri bed above. The key chemical reacti on is: 2Fe + 2H,0 + 0,

it'

2Fe(OH),

The reaction is dri ven by the lligher oxidat ion potential on the left s ide of the equation. T he net result is loss of

PRACTICAL TIP Except in cases where an unusually small implant has been used in error, most instances of fatigue failure of implants encountered in small animal practice result from stress concentration effects (often with other mechanical phenomena) acting in an unstable or poorly reduced fracture. Recommendations to use complex rath er than unil atera l sing le bar external fi xa to r frames in inherently unstab le fractures, or to use larger implants when appl ying a plate as a buttress, represent a recognition that in so me circumstances there is an increased risk of implant fatigue failure. Intuiti vely, we know that a plate over a poorly reduced fracture w ill be exposed to greater stresses th an a plate over an anatomicall y reconstructed bone, but th e full consequence in terms of the amount of increased stress may not be immediate ly obvious. Area moment o f inertia (AMI), discussed in Chapter 3 in relation to the biomechanics of fracture repair, is an expression of a structure 's ability to resist bending. AMI depends not only on the mass of material but also, and importantly in this contex t, on th e d istance o f mass fro m the neutral ax is of the structu re. The neutral ax is is that part of a structure under bend ing (or eccentric ax ial loading) which is

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Implant Failure 315 ex posed to neither tensile nor compressive force, and the imponance of estimating the neutral axis (and AMI) of a proposed bone-implant composite during fracture repair has been described in Chapter 3. Figure 24.4a shows an anatomically reduced fracture fixed with a plate applied to the lateral (tension) aspect of the femur. The neutral axis is displaced laterally but remains wi thin the bone. In Figure 24.4b the neutral axis lies within the plate itself; consequently, the AMI in this example is low, not only because the bone does not contribute, but also because the mass of the plate is close to the neutral axis. PRACTICAL TIP In essence, the presence of a mechanically competent cortex opposite a bone plate not only shares the load but also greatly enhances the mechanical environment by moving the neutral axis away from the plate. The low resistance to bending (low AMI) characterized in Figure 24.4b, which accelerates fatigue failure, will at the same time permit movement at the fracture. This may delay fracture healing, and therefore funher increase the risk of implant failure. The possibility of implant failure in this situation is recogni zed by most orthopaedic surgeo ns, who will avoid leaving fracture gaps or an open opposite conex. When unavoidable, the use of cancellous bone autografts will encourage prompt new bone fonnation, thus restoring mechani-

cal competence to the opposite conex and easing the stress acting through the implant. The broken plate shown in Figure 24.5 is a good example of fatigue fa ilure resulting from stress concentration in an implant caused by the lack of a mechanical ly competent opposite cortex . It is tempting to think that the plate was just too small. While a larger implant might have delayed failure, it probably would not have prevented it as the plate (no matter how large) remains mechanically ex posed. Had the cranial conex been reconstructed, the AMI would have been increased and the stress levels in the plate consequentl y decreased. An altemati ve solution would ha ve been the app lication ofa second plate. This would have been beneficial because of load sharing and, more importantl y, because of the effect of increasing the AMI of the repair. Tn conclusion, it is clear that most implant failures can be avoided and that implant fa ilure must not be considered an inevitable complication of fracture surgery. An awa reness of material failure, stress concentration, fatigue failure, etc. will help the aspiring fracture surgeon to avoid the technical errors that cu lminate in implant failure.

(b)

Figure 24.4: (a) Anatomically reduced midjemoral/ractllre fixed wi!/] a plate and screws. Th e dashed line represents rile estimated location 0/ the neutral axis. Because there is a mass 0/ material located some distance from tile lIeutral axis (plate laterally alld cortex mediaLLy) this bone and plate composite wiJJ have a high area o/movement a/inertia (high resistance to bending ) alld so will be inherel11ly stable. (b) A s imilar / racwre, but without benefit 0/ a mechanically competent medial/emoral cortex. Here, tile neutral axis must lie within the plate ilseij and so tile AMI;s very /IIucltlower. Weighrbearillg ill this limb will cause repeated bending stresses concentrated in the small part a/the plate overlying the fractu re - a recipe for fatigue failure.

Fig",.e 24.5: Lateral radiograph taken 4 weeks after open redllction and jixCl!iol1 of (/ comminuted intercondylar fra clllre of (he dista l humerus ill a 25 kg dog. Early progress had been ex ceJlellf alld the patient was only slightly lallle ulltii the plate snapped the day before this radiograph was taken. Note the large cranial cortical f ragmellf which was 110 r reduced and fixed ill the original repair.

REFERENCES AND FURTHER READING Nordin M and Frankel VH ( 1989) Basic Biomechanics oflhe MusculoSkeletal System , 2nd cdn. Lea and Febi gcr, Philadelphia. Pe rrcns SM and Rahn BA ( 1978) Biomechanics of fra cture healing, Orthopaedic Su rvey 2(2) 108- 143. Rad jn EL, Rose RM , Blaha JD and Litsky AS ( 1992) Practical Biomechanic!.jor the Orthopedic Surgeon , 2nd edn. Churchill Livingstone, New York. Sumner-Smith G (ed.) (1982) BOlle ill Clillical Orrhopedics. WB Saunders, Philadelphia.

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CHAPTER TWENTY FIVE

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Osteomyelitis Angus A. Anderson

INTRODUCTION Osteomyelitis is defined as inflammation of the bone cortex and marrow. Osteitis, myelitis and periostitis refer to inflammation in volving the bone cortex, marrowand periosteum, respecti vely. Although most commonly caused by bacteria, other infectious agents (fungi , viruses) may calise the disease, and corrosion of metallic implants may also initiate inflammatory responses in bone.

Osteomyelitis is often classified as being haematogenous or post-traumatic in origin. Post-traumatic osteomyelitis develops fo llowing the direct inoculation of bacteria into a fracture site either althe time the fracture occurs, or after contaminati on of th e fracture

site during internal fi xation, or by extension of infection fro m adjacent soft tissues (e.g. following bite wounds). Haematogenous osteomyelitis results from blood-borne bacteria locali zing to bones, butthesource of these bacteria is frequently unknown . Although there is no very satisfactory definition that distinguishes acute fro m chronic forms of the disease, chronic osteomyelitis is usuall y characterized by the presence of avascular co rtical bone and requires surgica l inter-

vention for the disease to resolve. Some bacteria (e.g. Mycobacteria spp.) and some fungi give rise to a disease that is chronic in nature.

PATHOGENESIS Normal bone is relatively resistant to infection and studies of animal models of osteomyelitis have shown that chronic disease can only be generated if a number of factors are present. These include: An inoculum of suffi cient numbers of pathogenic bacteria Avasc ular cortical bone Favourable environment fo r bacterial coloni zation and multiplication (metallic im plants, haematomata, necrotic soft tissue).

Chronic osteomyelitis is unli kely to develop if these three factors are not present (Braden et ai. , 1987).

Unfo rtunately, the commonest reason fo r the development of osteomyelitis in small ani mals is the open reduction of fractures. During surgery, bacteria from the animal 's skin, the atmosphere or the surgeon frequently contaminate the exposed tissues and may coloni ze the surface of metallic implants (Smith et al. , 1989). Some bacteria possess mechanisms that ensure their persistence at fracture sites. These include the prod uct ion of sli me that consists of extracellular polysaccharides, ions and nutrients (Gristina et ai., 1985), phenotypic transformation to more virulent strains, and adherence to components of extracellular matrix (e.g. fi bronectin, laminin) via specific receptors (Vercelotti etal. , 1985). Bacteri al slime combines with host-deri ved substances to fo rm biofilm, which surrounds bac terial colonies and protects them fro m host defences (phagocytosis, anti bodies and complement) and the actions of some antibiotics (Figure 25.1). Despite the high incidence of contamination during surgery, osteomyelitis only develops in a small proportion of cases (Smith et ai., 1989) . Fac tors that increase the likelihood of the development of infection include excessive trauma to soft tissues, periosteal stripping resulting in devascularization of cortical bone, fracture instability, and the presence of individual host factors that may alter local defences (e.g. malignancy, diabetes mellitus). If infection becomes established, inflammatory exudate may be fo rced along the Haversian and Volkmmm 's canals of the cortex, under the periosteum (particularl y in young animals where the periosteum is more loosely attached to underlying cortical bone) and into the medullary canal (Figure 25.1 ). Fragments of cortical bone that have lost their blood suppl y (sequestra) may become surrounded by exudate and act as persistent foc i of infection . The periosteum and endosteum of cortical bone adjacent to a sequestrum may attempt to wall off this infected material by depositing new bone (involucrum) around it. Fracture instability is an. important mechanism potentiating infection. Lysis of cortical bone adjacent to implants, as a result of the infection, may lead to implant loosening and increased interfragmentary moveme nt. Th is effect may be compounded by excessive movement at the fracture site caused by

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318

Manual of Small Animal Fracture Repair and Management inadequate fracture fixation, or technical errors in

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