Tibiotarsal fracture repair I

in a scarlet macaw using external skeletal furatio; Surgical repair of a fractured

tibiotarsus in a scarlet macaw

(Ara macao) is described. The

forces imposed on the fracture

site are discussed and the

unique features of avian bone

emphasised. Advantages of

external skeletal fixation and

specific details of the frame

construction are highlighted.

M. KAVANAGH

Journal of Small Animal Practice (1997) 38. 296-298

147 Mill Lane, Northfield, Birmingham 1331 2RN

INTRODUCTION

Tibiotarsal fractures are among the more common orthopaedic problems encoun- tered in caged birds (Redig 1986a). Their management must include consideration of some special features of avian bone. Avian bone has thinner cortices and is more brittle than mammalian bone. I t is more likely to shatter during surgery (Withrow 1982). It lacks haversian systems and the medullary cavity is traversed with boney struts that play an important part in the overall strength of the bone (Coles 1985). Endosteal blood supply and endosteal callus formation are particularly important to avian fracture healing (Bush and others 1976). This has important implications if intramedullary implants are used (Bush 1980).

Due care and attention must be paid to the postoperative care of the patient and its long-term future. Destructive, powerful birds may quickly shred the stoutest ofcast materials. Birds which are to be returned to the wild will need to have near perfect function if they are to survive.

CASE HISTORY

A 17-year-old male scarlet macaw (Ara rnacao) was presented with a lameness of 2 4 hours duration. It had caught its right foot in some cloth that had been wrapped round a perch. It was acutely lame follow- ing a struggle to free itself. O n examina- tion, the bird was 5 / 5 lame on its right leg. Clinical examination demonstrated crepi- tus in the tibiotarsal area. A fracture was diagnosed and further investigation advised.

The bird weighed 850 g and was given 0.1 rnl each of xylazine (Rompun; Bayer) and ketamine (Ketaset; Parke Davis) intra- muscularly as recommended by Harrison (1986). It was necessary to give an addi- tional 50 per cent of this dose after a further 10 minutes and 2 5 per cent of the initial dose again at 20 minutes after induction to maintain anaesthesia suffi-

FIG 1. Ventrodorsai view of the right tlblotarsus. showing the proximal transverse fracture

cient for radiography. A proximal trans- verse fracture of the tibiotarsal bone wx*l diagnosed (Fig I ) and surgical repair advised.

Surgical technique T h e bird was taken direct to theatre. a i d anaesthesia was mainrained with 2 per cent halothane vaporised in oxygen a t ;i flow rate of 2 litres/minute administered vi.1 ;I face mask. Bubble wrap was used to inbii- late the bird. Minimal numbers offeather\ were plucked at the surgical sire, again t o reduce body heat loss. The area W J ~ roil- tinely scrubbed with chlorhexidine glu- conate (Hibiscrub Vet; Mallinckrodr) i n warm water, avoiding excessive wetting o f the feathers, and 0.25 ml anioxycillin (Vidamox; BK) was given subcutaneoiisly Using small stab incisions, four parallel 1 1 mm K-wires were driven through both cortices of the tibiotarsus using a handheld chuck - two in the proximal segment and two in the distal segment. A uniplanar rypc I1 Kirschner-Ehnier external fix;ttoi- U ' J ~ applied.

Connect i ng bars were i n it ia I l y a p p I i cci to the transverse pin using cerclagc wire. This allowed an assessment of the align- ment of the fracture and suitable adjiisr- ments to be made before anchoring rhc wires firmly in position with polymcrhyl- methacrylate (Tecnovet 6091 ; Kulzct-1. The bone length and orientation of digits

FIG 2. Postoperative radiographs emphaslsing the Importance of taking more than one view. Reduction and alignment appear excellent In the ventrodorsai vlew (A). The medloiaterai radiograph (B) shows that, although ilmb length has been maintained compared with the other leg, there is displacement of fracture fragments

and leg wcre first assessed visually m d by referencc to the other leg, after which methylmethacrylate was applied. Post- operativr ridiography showed reasonable alignment although reduction at the frac- ture site WJS poor (Fig 2). Anaesthetic recovery \\I\ smooth and uneventfiil. Total anaesthetic time was a little over one hour. The bird w.is discharged with amoxycillin capsules (Amoxycillen 250; Millpledge) at a rate of 250 ing once daily dissolved in the drinking water for 10 days. Cage rest was advised.

Follow-UP Six weeks later the bird was using the leg well. I t had paid little attention to the fixator, which was undamaged. An Elizabethan collar had been provided but the owner had removed this after several unsuccessful attempts to replace it after removal by the bird.

General inaesthesia was repeated at this time, with a single dose of 0.1 5 ml each of xylazine and ketamine administered intra- muscularly. Radiographs were taken. Bridgingcallus was evident (Fig 3) with no signs of pin loosening (confirmed clini- cally). The niost proximal pin on each side of the fracturc site was cut on the medial side. This eftcctively weakened the frame and transferrcci more of the weightbearing load onto the bone. Controlled stress across the fr.acture speeds the rate and

FIG 3. Ventrodorsai radlograph at six weeks. Bridging callus has spanned the fracture site. There is no excess callus and no lucency surrounding the transverse pins. The fracture site is stable

improves the quality of healing (McKibbin 1978). Supervised exercise on a non-slip surface was advised over the next month.

A third series of X-rays was taken at 1 1 weeks, at which point the callus was remodelling with osseous union evident (Fig 4) . The fixator was removed and, clin- ically, the bird had full use of the limb.

The same principles of fracture repair apply to avian species as to the more usual veterinary patients. Consideration must be given to the impact of trauma on the sur- rounding soft tissues and the distractive forces that must be countered for success- ful fracture repair. Generally, the more comminuted the fracture the more severe the soft tissue damage. Bone fragments need a good blood supply to be involved in the repair process. Any surgical procedures that disturb this blood supply will hinder fracture healing.

The initial poor alignment and instabil- ity of the fragments in this case meant that some form of rigid fixation was necessary to overcome the compressive, shearing, rotational and bending forces imposed on the fracture site. Distal limb fractures in birds are especially prone co rotation (Coles 1985). Simple casts will not oppose these forces and would also be subject to damage by the bird. Macaws beaks are

FIG 4. Ventrodonal (A) and medlolateral (B) radiographs at ll weeks. Callus remodelling has taken place with bridging of the fracture site. There is no evidence of pin ioosenlng

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vcry powerful and capable of shredding most materials. Intramedullary pinning is well described (Roush 1980) but it will not counteract rotation at the fracture site and it also destroys, at least temporarily, the intraniedullary blood supply thus prevent- ing endosteal callus formation. This has hcen shown to be particularly important in w i a n fracture repair (Bush and others 1076). 111 addition, the surgeon risks inva- sion of a joint surface either proximal or distal to the fracture site. Plates are a pos- sibility but the thin cortices of the bone give poor screw grip and a more extensive surgical procedure is required.

T h e external skeletal fixator is ideal in this situation as it addresses all the destabil- ising forces, preserves the intramedullary blood supply, avoids soft tissue damage close ro the fracture site and is robust enough to survive on the bird's leg. Early limb use is possible, which helps to main- tain muscle tone and joint movement. T h e incidence of fracture disease is reduced. Additionally, it allows the fracture callus to be progressively loaded by staged removal and it is cheap and relatively quick to apply .ind remove.

In this case, the fixator frame bore almost all the weight with early limb use because of the poor reduction at the frac- ture site. However, by six weeks the callus had bridged the fracture gap and this allowed the bone to resume its weightbear- ing function. Cutting two ofthe transverse pins weakens the fixator frame, increasing loadbearing on the bone at the fracture site. This callus loading procedure facili- tates healing, encouraging bone deposition in response to Wolff's law - ie, the internal architecture and external form of a bone are related to its function and change when the function is altered. O n clinical exarni- nation the frame was found to have remained rigid with no niediolateral rnove- ment.

Secondary fracture disease such as nialunion is a major complication and must be prevented. With prolonged disuse of the fractured leg, the limb musculature will become atrophic and joint capsules

will fibrose causing reduced range of movement. Excessive periosteal callus can reduce dexterity (Bush 1977), as tendons become trapped in the callus or displaced. In heavy birds particularly, consideration of the effects of prolonged excessive weight- bearing on the sound limb is essential. Abnormal overuse of the sound leg can result in pressure necrosis and open sores developing on the foot which may allow a pododermatitis (bumblefoot) condition to develop (Redig 1986b). Bumblefoot can itself be a crippling disease which is diffi- cult to treat and its development on the sound limb may result in eventual euthanasia.

Parrots use their feet extensively in feed- ing, and inability to use a fractured limb may reduce feed intake. It is important that both feet are fully functional as the bird needs one foot to manipulate its food and the other to take its total bodyweight (N. A. Forbes, personal communication). The fixator used here avoided these prob- lems; the bird began to use the leg to sup- port its bodyweight within a few days of surgery and progressively took more weight thus avoiding overuse of the normal left leg. The device weighed 16 g, which is rela- tively light for a bird of this size, and the weight of the fixator frame did not hinder the bird's ability to use the leg.

The author believes the technical details of the frame used in this case are important to the strength of the finished device. The use of plastic casting materials to construct the connecting bars - the Boston Technique - was reported by Sat- terfield and O'Rourke (198 1). This results in a lighter frame but, as Redig (1 986b) comments, the weight of the 'hardware' is irrelevant for large parrots. Using poly- rnethylmethacrylate alone to fashion the connecting bars results in a very small area of contact between the cement and the smooth surface of the pins. Bending the exposed ends of the transverse pins at 90" to increase the area of contact, has been reported. However, it is technically diffi- cult to align all the bends correctly, with the result that neighbouring pins tend to

obstruct manipulation of each other. Care is needed to avoid excessive force being transmitted to the brittle bone while creat- ing the angles, otherwise surgical reduction is disturbed. T h e surgeon should take into account the brittleness of avian bone.

By using pins or K-wires as connecting rods joined by cerclage wire to the trms- verse pins in the bone, the surgeon can assess the adequacy of the fracture reduc- tion and limb alignment before conimit- ting to the rigidity ofcured acrylic cement. Also the author believes the cerclage wirc offers a larger surface area to the cenient, helping it to form a better grip on thc metal surfaces. The author has used thi\ 'clamping' mcthod extensively evcn i n quite large dogs with good results. (k- tainly in very small animals and birds thc surgeon must consider the e x t n weight of the steel connecting rods but this w u not considered relevant in this case.

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BUSH. M.. MONTALI. R. J . . NOVAK. G. R. & J ~ M F ~ . A. E (1976) The healing of avian fractures: a histological xeroradiographic study. Journal of the American h i ma1 Hospital Assooation 12, 768-773

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REDIG. P. T. (1986a). Evaluation and nonsurgical iiiim agement of fractures. In: Clinical Avian Medicine ant1 Surgery. Eds G. J. Harrison and 1. S. Harrisori W B. Saunders. Philadelphia. pp 380-394

REOIG. P. T. (1986b). Basic orthopaedic surgical tech niques. In: Clinical Avian Medicine and Surgery. Eds G. J. Harrison and J . S. Harrison. W. B Saunders. Philadelphia. pp 596-598

ROUSH. J. C. (1980) Avian orthopaedics. In: Current Vet erinary Therapy VII. Ed R. W. Kirk. W. 8. Saunders. Philadelphia. pp 662-673

SATTERFIELD. W. & O'ROURKE. K. I. (1981) External shelc tal fixation in avian orthopaedics using a modified through-and-through Kirschner-Ehnier splint Tech nique (the Boston technique). Journal of the Aiiierr can Animal Hospital Association 17. 635-637

WITHROW. S. J. (1982) General principles of fracture repair in raptors. Compendium on Continuing Edi i cation for the Practicing Veterinarian 4. 116 121

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