Arthrodesis of the scapulohumeral joint in a horseDave G. MacDonald, Jerry V. Bailey, J. Dave Fowler

A 12-month-old, 250 kg, Arabian filly was referred tothe Veterinary Teaching Hospital, Western College

of Veterinary Medicine at the University of Saskatchewan,for evaluation of lameness of the right forelimb. The filly,which had been turned out in a paddock with severalother yearlings, was nonweightbearing on the rightforelimb and resisted palpation of the right shoulder.At presentation, she demonstrated a grade 5 of 5 lame-ness of the right forelimb. The area over the right shoul-der was edematous, but crepitation was not detected. Shewas able to advance the leg, and had normal skin sen-sation all over the limb. Lateromedial and caudocranialradiographs of the right scapula and shoulder revealeda fracture of the supraglenoid tubercule with involvementof the cranial one-third of the glenoid cavity and dis-location of the scapulohumeral joint (Figure 1). Due tothe size of the fragment and the amount of articularsurface involved, it was felt that surgical stabilization byopen reduction and internal fixation would yield themost favorable prognosis.

dis-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..

Figure 1. Lateromedial radiographic view showing a dis-placed fracture (arrow) of the right supraglenoid tubercule.

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Department of Veterinary Anesthesiology, Radiology andSurgery, Western College of Veterinary Medicine, Universityof Saskatchewan, Saskatoon, Saskatchewan S7N OWOThe authors wish to thank Bayvet Division Chemagro Ltd. forsupplying the enrofloxacin used in this case.

Following induction of anesthesia, the filly wasplaced in left lateral recumbency, and the right shoulderand humerus were prepared and draped for asepticsurgery. A 25 cm long skin incision was made, com-mencing at the distal end of the spine of the scapula,crossing the scapulohumeral joint, and continuing overthe lateral surface of the humerus to the level of thedeltoid tuberosity. The deep fascia was incised, expos-ing the caudal border of the brachiocephalic muscle. Themuscle border was elevated and reflected cranially toexpose the underlying dense aponeurotic origin of thedeltoid muscle. The aponeurosis was transected andthe deltoid muscle retracted caudally, revealing theteres minor muscle. The insertion of the teres minormuscle on the humerus was transected and the musclebelly retracted in a caudal direction. The exposed scapu-lohumeral joint capsule was incised parallel to therim of the glenoid cavity. A 7 cm3 fragment of thesupraglenoid tubercule with approximately one-thirdof the articular surface of the glenoid cavity was dis-placed in a craniodistal direction. The humerus wasreadily reduced to its correct anatomical location; how-ever, efforts to reduce the fracture fragment were futile,even after partial severance of the attachments of thebiceps and coracobrachial muscles to the supraglenoidtubercule and coracoid process, respectively. The frag-ment was subsequently freed from its attachments andremoved. The scapulohumeral joint was lavaged withcopious amounts of sterile saline and the edges of thefibrous joint capsule were apposed with 2-0 polydiox-anone (Ethicon Sutures Ltd., Peterborough, Ontario) ina continuous pattern. A closed suction drain (SynderHemovac Polyvinyl Chloride Drain, Zimmer, Dover,Ohio) was placed to exit through the skin dorsal andcranial to the incision. The insertion of the teres minormuscle was reattached to the humerus and the aponeu-rotic origin of the deltoid muscle was sutured with 2 poly-dioxanone in an interrupted pattern. The free caudalborder of the branchiocephalic muscle was replacedover the deltoid muscle and sutured with 0 polydiox-anone. The subcutaneous tissue was closed in a continuouspattern with 0 polydioxanone and the skin was apposedwith stainless steel staples (Auto Suture, United StatesSurgical Corporation, Norwalk, Connecticut). The filly'ssize and temperament allowed her to be manuallyrestrained and assisted to her feet during recovery fromanesthesia. Postoperatively, a combination of sul-famethoxazole and trimethoprim (Apo-Sulfatrim,Apotex Inc., Weston, Ontario) was administered at30 mg/kg body weight (BW), PO, ql2h, for 7 d andphenylbutazone (rogar/STB, Pointe Claire, Quebec) at4 mg/kg BW, IV. The phenylbutazone was continued,PO, daily and the dose was tapered as the filly becamemore comfortable. Evacuation of the closed suctiondrain was performed as required. The lameness did notimprove significantly, and radiographs of the shouldertaken 8 d following surgery showed that proximalluxation of the humeral head had recurred. A decision todo an arthrodesis of the right scapulohumeral joint was

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Figure 2. Postoperative radiograph of the right scapulo-humeral arthrodesis.

made. Prior to surgery, the standing angle of the leftscapulohumeral joint was measured at approximately1200, which served as a reference for determining theangle of our arthrodesis.

Following induction of anesthesia, the filly was placedin left lateral recumbency and the right shoulder andhumerus were prepared and draped for aseptic surgery.A 40 cm long skin incision was made cranial to theprevious incision, beginning at the middle of the scapula,following the spine distally, and continuing over thelateral surface of the humerus to the midpoint of itsshaft. The deep fascia was incised and, although theanatomy was somewhat distorted due to the previoussurgery, the caudal border of the brachiocephalic musclewas identified and elevated cranially. An osteotomyof the deltoid tuberosity enabled the deltoid muscle to beretracted caudad, while osteotomy of the greater tuber-cle facilitated dorsal reflection of the supraspinatusmuscle. Deep to the supraspinatus muscle, a smallpocket of purulent material was encountered, extendingdeep towards the joint. A swab of this exudatewas taken for routine microbiological culture andsensitivity testing. The incision was lavaged with copi-

Can Vet J Volume 36, May 1995

ous amounts of sterile physiological saline-. The infra-spinatus muscle was reflected by transection of its ten-don, exposing the joint capsule, which was then incised.Portions of the neck of the scapula and the head of thehumerus were excised with an oscillating saw at the pre-determined angle of 1200. With the cut surfaces of thescapula and humerus apposed, 2, 4-mm Steinmann pins(OTI, Timonium, Maryland) were driven caudodor-sally from a position distal to the greater tubercle of thehumerus into the neck of the scapula to maintain thereduction. A broad 4.5-mm, 18-hole, dynamic com-pression plate (Synthes Canada Ltd., Mississauga,Ontario) was contoured and applied over the craniolat-eral aspect of the spine of the scapula and distally overthe cranial aspect of the humerus (Figure 2). Cancellousbone was harvested from the humeral head and packedaround the osteotomy site. A closed suction drain wasplaced adjacent to the plate to exit through the skin,dorsal to the incision. The deltoid tuberosity, greatertubercle of the humerus, and tendon of the infraspinatusmuscle were repaired with 2 polydioxanone sutures.The braciocephalic muscle and deep fascia were closedwith 2 polydioxanone in simple continuous patterns. Theskin incision was closed with stainless steel staples.The filly was again manually restrained and assistedto her feet during recovery from anesthesia.While awaiting the results from the culture and sen-

sitivity testing, cefazolin sodium (Kefzol, Eli LillyCanada Inc., Scarborough, Ontario) was administered at20 mg/kg BW, IV, q6h. Staphylococcus aureus andStreptococcus fecalis were cultured and the S. fecalis wasshown to be resistant to most common antibiotics, withthe exception of enrofloxacin. The filly was started ona 13-wk, 25 mg/kg BW, PO, ql2h regimen of enrofloxacin(Baytril, Bayvet Division Chemagro Ltd.). Postopera-tively, the filly would bear weight on the right forelimb;however, she required assistance to advance the limbwhen walking. Physiotherapy in the form of passiveflexion of the carpus and daily walking was initiated, andshe made a gradual improvement. Four weeks followingsurgery, she was able to advance the right forelimband bear full weight but exhibited an obvious gaitabnormality.

Fourteen weeks following surgery, the filly began toexhibit an increased amount of discomfort associatedwith the right forelimb, and a draining tract from the ven-tral aspect of the incision was noticed. She was returnedto the Western College of Veterinary Medicine, atwhich time clinical examination and a sinogram showedthat the draining tract communicated with the plate.A swab of the exudate was taken for routine microbio-logical culture and sensitivity testing. Radiographs takenat this time revealed good apposition and alignment ofthe arthrodesis with an increased production of bone sub-stance at the scapulohumeral interface; however, bonefusion was still incomplete. Several screws were dis-placed and one screw in the humerus had broken.Although arthrodesis was incomplete, we felt there wasenough structural support present to allow removal of theimplant.The filly was placed in left lateral recumbency and the

right shoulder, humerus, and tuber coxae were preparedfor aseptic surgery. The same surgical approach used toapply the plate was modified (due to scar tissue) to

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Figure 3. Lateromedial radiograph of the right scapulo-humeral arthrodesis 1 y postoperatively. A broken screwremains in the proximal humerus.

remove the plate. The one broken screw was submittedfor routine microbiological culture and sensitivity test-ing. A cancellous bone graft was taken from the tubercoxae and packed around the site of arthrodesis. A 1.5 cmPenrose drain exited distal to the skin incision. Herrecovery from anesthesia was once again assisted.Streptococcus zooepidemiccus and S. aureus were cul-tured from the screw, and both microbes were sensitiveto the combination of sulfamethoxazole and trimetho-prim, which was administered at 30 mg/kg BW, PO,ql2h. The postoperative production of exudate fromthe drain decreased steadily, and after 6 d, the drain wasremoved. She made an uneventful recovery and wasdischarged 14 d following the 3rd surgery. One year post-operatively the filly is turned out to pasture with severalother 2-year-olds. Although the filly has a mechanicallameness, presumably due to the apparent shortening ofthe right forelimb, she is able to remain a part of the herdat pasture. Radiographs of the shoulder show completearthrodesis (Figure 3).

Shoulder lameness is uncommon, occurring mostoften in horses less than 3 y of age. Osteochondrosis andosseous cyst-like lesions are the most common cause ofshoulder lameness in young horses; nevertheless, frac-tures of the scapula or the proximal end of the humerusmust be considered in the differential diagnosis for ahorse with clinical signs of lameness of the upper fore-limb, especially if there is a history of trauma (1). Fractureof the supraglenoid tubercule is usually a sequel totrauma from collision with a solid object or anotherhorse, or perhaps a fall (2). The supraglenoid tuber-cule and coracoid process develop from a single centerof ossification and fuse with the cranial portion of the

glenoid cavity and the main body of the scapula atabout 1 y of age (3). Anatomically, the supraglenoidtubercule is the most cranial prominence of the scapulaand forms the point of the shoulder. It serves as theorigin of the biceps muscle and the 2 glenohumeralligaments that support the scapulohumeral joint capsule.

Suggested treatments for fractures of the supraglenoidtubercule in the horse have included conservative man-agement, removal of the fracture fragment, and variousmethods of internal fixation (2,4-6). Excision of the frag-ment can eliminate the pain associated with movementat the fracture site by means of a less technically demand-ing procedure than internal fixation. Excision of thefragment may also remove mechanical interferencewith full extension of the scapulohumeral joint, eliminateincongruent joint surfaces, and thus limit the progressionof degenerative joint disease (4). Previous attempts atinternal fixation that combined lag screws or Kirschnerwires with tension-band wiring have not been success-ful (2,7). Implant failure in these cases has been attrib-uted to the distracting forces from the tendons of thebiceps and coracobrachial muscles and the poor holdingpower of implants in the porous bone of the scapular neck(7). There are only 2 reports of successful repairs inthe adult horse. Pankowski et al (5) utilized a partialtenotomy of the biceps tendon and placement of 2,6.5-mm cancellous screws with cerclage wires in a ten-sion band fashion across the fracture line, while Dart andSnyder (8) placed 3, 5.5-mm cortical screws across thefracture line in a lag fashion.

In the dog, arthrodesis of the scapulohumeral joint canmarkedly improve function when severe degenerativejoint disease, chronic luxation, or comminuted scapu-lohumeral fractures result in a nonfunctional joint(9-12). Arthrodesis of the scapulohumeral joint hasalso been reported in 1 miniature horse with degenera-tive joint disease (13), but to our knowledge never in afull-sized horse or as an alternative in the treatment offractures of the supraglenoid tubercule. In this case,reduction of the fracture fragment was not possible andremoval of the fragment resulted in gross instabilityof the scapulohumeral joint. Arthrodesis of the scapu-lohumeral joint was considered to be feasible because ofthe horse's size and temperament, and the owner'sdesire to salvage the filly as a broodmare. The apparentshortening of the right forelimb was probably the resultof bridging the proximal humeral growth plate. Closureof the proximal humeral growth plate in the horseoccurs between 26 and 42 mo of age (3). The amount ofgrowth potential remaining in the proximal humeralphysis has not been established for a yearling; how-ever, it is very likely that bridging the physis did arrestlongitudinal growth of the humerus.

Attempts at scapulohumeral arthrodesis in the horsemay be limited to smaller breeds and immature ani-mals because of the possibility of implant failure inheavier animals. Based on the outcome of this case,scapulohumeral arthrodesis should be considered atreatment option in selected cases when internal fixationof fractures of the supraglenoid tubercule is not possibleand removal of the fragment results in gross jointinstability. cvi

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References1. Dyson SJ. Diseases of the shoulder. In: Colahan PT, Mayhew IG,

Merritt AM, Moore JN, eds. Equine Medicine and Surgery, 4th ed.Goleta, California: American Veterinary Publications, 1991:1451-1456.

2. Dyson SJ. Sixteen fractures of the shoulder region in the horse.Equine Vet J 1985; 17: 104-1 10.

3. Getty R. Equine osteology. In: Getty R, ed. Sisson and Grossman'sThe Anatomy of the Domestic Animals, 4th ed. Philadelphia:WB Saunders, 1975: 273-276.

4. Wagner PG, Watrous BJ, Shires GM, Riebold TW. Resection ofthe supraglenoid tubercle in a colt. Compend Contin Educ Pract Vet1985; 7: 536-540.

5. Pankowski RL, Grant BD, Sande R, Nickels FA. Fracture of thesupraglenoid tubercle treatment and results in five horses. Vet Surg1986; 15: 33-39.

6. Adams SB. Surgical repair of a supraglenoid tubercle fracture ina horse. J Am Vet Med Assoc 1987; 197: 332-334.

7. Leitch M. A review of treatment of tuberscapulae fractures in thehorse. J. Equine Med Surg 1977; 1: 234-240.

8. Dart AJ, Snyder JR. Repair of a supraglenoid tuberosity fracturein a horse. J Am Vet Med Assoc 1992; 201: 95-96.

9. Fowler JD, Presnell KR, Holmberg DL. Scapulohumeral arthrode-sis: Results in seven dogs. J Am Anim Hosp Assoc 1988;24: 667-672.

10. Vasseur PB. Arthrodesis for congenital luxation of the shoulder ina dog. J Am Vet Med Assoc 1990; 197: 501-503.

11. Moore RW, Withrow SJ. Arthrodesis. Compend Contin EducPract Vet 1981; 3: 319-330.

12. Brinker WO, Piermattei DL. Handbook of Small AnimalOrthopedics and Fracture Treatment. Toronto: WB Saunders,1983: 364-366.

13. Arighi M, Miller CR, Pennock PW. Arthrodesis of the scapulo-humeral joint in a miniature horse. J Am Vet Med Assoc 1987; 191:713-714.

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