Introduction

A 13-year-old 128-kg miniature donkey gelding was admitted with right forelimb lameness (grade, 4/5)¹ of 7 weeks’ duration. No improvement had been observed for a period of 7 weeks since the time of injury. Trauma was suspected as the cause of lameness. Abnormal physical examination findings included muscular atrophy of the right supraspinatus and infraspinatus muscles, a palpable prominent greater tubercle of the humerus, and adduction of the distal aspect of the limb. At the walk, the cranial phase of the stride was reduced with dragging of the toe and partial weight-bearing on the limb. No neurologic deficits were observed. On the basis of physical examination findings, luxation of the shoulder joint was suspected.

With the donkey in a standing position, mediolateral and craniocaudal radiographic views of the right shoulder joint were obtained. Shoulder joint radiography revealed lateral luxation and bony remodeling of the right humeral head (Figure 1). Surgical options, including closed reduction, open reduction, shoulder joint arthrodesis, and glenoid ostectomy, were discussed with the owner. On the basis of chronicity, we did not believe closed or open reduction would be possible, leaving shoulder joint arthrodesis and glenoid ostectomy as viable options. Glenoid ostectomy for chronic luxation or osteoarthritis of the shoulder has been previously reported for dogs.^2–6 These options were discussed with the owner, and they concluded that shoulder joint arthrodesis was not a financially viable option. Therefore, the owner elected for glenoid ostectomy if either open or closed reduction of the shoulder joint luxation was not possible.

Preoperative craniocaudal radiographic view of the right shoulder joint with lateral luxation of the humerus in relation to the scapula with bony proliferation and remodeling of the humeral head.

Citation: Journal of the American Veterinary Medical Association 259, 9; 10.2460/javma.259.9.1043

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Preoperative craniocaudal radiographic view of the right shoulder joint with lateral luxation of the humerus in relation to the scapula with bony proliferation and remodeling of the humeral head.

Citation: Journal of the American Veterinary Medical Association 259, 9; 10.2460/javma.259.9.1043

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Preoperative craniocaudal radiographic view of the right shoulder joint with lateral luxation of the humerus in relation to the scapula with bony proliferation and remodeling of the humeral head.

Citation: Journal of the American Veterinary Medical Association 259, 9; 10.2460/javma.259.9.1043

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Penicillin G potassium (22,000 U/kg, IV), gentamicin sulfate (6.6 mg/kg, IV), phenylbutazone (4.4 mg/kg, IV), and a tetanus toxoid vaccine (IM) were administered prior to anesthetic induction. Sedation prior to induction of general anesthesia consisted of administration of xylazine hydrochloride (0.78 mg/kg, IV) and butorphanol tartrate (0.04 mg/kg, IV). Anesthetic induction was achieved by administration of midazolam (0.12 mg/kg, IV), ketamine (2.3 mg/kg, IV), and guaifenesin (50 mg/kg, IV). General anesthesia was maintained with isoflurane (2% to 3%) in oxygen. The donkey was positioned in left lateral recumbency. Closed reduction was attempted unsuccessfully via traction with a come-along winch prior to continuing with open reduction and glenoid ostectomy. The hair overlying the surgical site was clipped and the area was aseptically prepped and draped, including draping of the distal aspect of the limb to allow manipulation of the limb.

A 20-cm-long craniolateral skin incision centered over the shoulder joint was made followed by sharp dissection through the subcutaneous layer and omotransversarius muscle with cranial retraction of the brachiocephalicus muscle. Tenotomies of the insertional tendons of the supraspinatus and biceps brachii muscles were performed, and the joint capsule was incised parallel to the joint surface. At the site of luxation, cartilage and bone erosion of the lateral aspect of the glenoid cavity of the scapula and the medial aspect of the humeral head was observed. Because of excessive fibrosis and the chronicity of the luxation, open reduction was not possible. An oscillating saw and osteotome were used to remove the glenoid cavity with a transverse ostectomy through the scapular neck, avoiding the suprascapular nerve. The joint capsule was sutured closed, and the tendons of the supraspinatus and biceps brachii muscles were reattached to their insertions with inverted cruciate and simple interrupted patterns with size-1 polyglactin 910. The omotransversarius muscle incision was closed in the same fashion. The subcutaneous layer was closed with a simple continuous pattern of size-0 polyglactin 910. Sterile saline (0.9% NaCl) solution containing gentamicin sulfate was used for incisional lavage, and stainless steel skin staples were used to close the skin. A stent bandage and iodine-impregnated incision drape were secured over the wound. Total surgical time was 1 hour and 14 minutes. Xylazine hydrochloride (0.23 mg/kg, IV) was given once in the recovery stall. Recovery from anesthesia was manually assisted with 2 handlers and was without complication.

After surgery, the donkey was able to intermittently stand, with the right forelimb underneath its body, and bear weight on the limb in the stall. At the walk, the donkey maintained a reduced cranial phase of the stride with mild improvement, compared with before surgery. The donkey received potassium G penicillin (22,000 IU/kg, IV, q 6 h), gentamicin sulfate (6.6 mg/kg, IV, q 24 h), and phenylbutazone (2.2 mg/kg, IV, q 12 h) for 5 days after surgery. Following discontinuation of IV administration of antimicrobials, trimethoprim sulfamethoxazole (30 mg/kg, PO, q 12 h) was administered for 7 days. The stent bandage was removed 3 days after surgery. Box stall rest was continued for the donkey for 2 months after hospital discharge before a gradual increase in exercise to full pasture turnout.

At 15 months after hospital discharge, a follow-up examination was performed at the teaching hospital. Supraspinatus and infraspinatus muscular atrophy was present but improved, compared with before surgery. There was no pain on palpation or on flexion and extension of the limb, and range of motion was comparable to the other forelimb. No lameness at the walk was observed; however, at a trot, a consistent but mild lameness (grade, 3/5)¹ was present with a subtle reduced cranial phase of the stride. Radiographs revealed bony remodeling of the glenoid cavity of the scapula and humeral head with formation of a pseudoarthrosis (Figure 2). The long-term outcome was considered excellent on the basis of absence of pain associated with the shoulder, functional use of the limb with improvement in lameness, and no postoperative complications. The owner was satisfied with the outcome and reported that improvement in lameness after surgery was gradual, with the most improvement observed in the 6 months prior to reexamination.

Fifteen-month postoperative mediolateral radiographic view of the right shoulder joint with chronic bony remodeling of the glenoid cavity of the scapula and humeral head with formation of a pseudoarthrosis.

Citation: Journal of the American Veterinary Medical Association 259, 9; 10.2460/javma.259.9.1043

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Fifteen-month postoperative mediolateral radiographic view of the right shoulder joint with chronic bony remodeling of the glenoid cavity of the scapula and humeral head with formation of a pseudoarthrosis.

Citation: Journal of the American Veterinary Medical Association 259, 9; 10.2460/javma.259.9.1043

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Fifteen-month postoperative mediolateral radiographic view of the right shoulder joint with chronic bony remodeling of the glenoid cavity of the scapula and humeral head with formation of a pseudoarthrosis.

Citation: Journal of the American Veterinary Medical Association 259, 9; 10.2460/javma.259.9.1043

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Discussion

Shoulder joint luxation in large animals is an uncommon orthopedic condition that can be characterized by non– to minimally weight-bearing lameness, gait alterations including reduced range of motion (reduced cranial phase of the stride) or a tendency to drag the limb, and pain upon palpation and manipulation of the shoulder.^7–9 Luxation of the shoulder is obvious upon physical examination because the greater tubercle of the humerus is displaced laterally and, with chronicity, there is disuse muscular atrophy overlying the shoulder joint. Sudden trauma is the most common etiology and is often assumed in cases where a cause is not identified.⁷ Miniature horses and ponies are overrepresented and may be predisposed to shoulder dysplasia as, at least in Shetland ponies, a shallower glenoid cavity leading to instability has been reported.^10–12 The prognosis for this problem is poor without treatment and worse with concurrent fractures and osteoarthritis.⁷ Although closed reduction has been successful in acute cases, the success rate is lower, compared with that of open reduction.^7,13–17 Many options for intervention have been attempted, such as open reduction and internal stabilization with biceps brachii tendon transposition, joint capsule imbrication, and lateral tension band sutures.^7,18–20

Shoulder joint arthrodesis with internal fixation has been reported for small and miniature horses.^18,19,21 Variations in the technique have been described and can include transarticular Steinman pins in addition to a dynamic compression plate with transarticular lag screws.^18,19,21 This technique is associated with the increased cost of internal fixation and has the risk of complications such as fractures, implant failure, and surgical site infection.^19,21 For shoulder joint abnormalities not amenable to restoration of joint function, shoulder arthrodesis yields good to excellent outcomes but can be associated with complication rates as high as 50%.^22–24 In dogs and cats, glenoid ostectomy with or without humeral head excision has been described as an alternative to shoulder joint arthrodesis.^2–6 The pseudoarthrosis that forms is characterized by sclerosis of the ends of bone and creation of fibrocartilage and a fibrous capsule, which is caused by motion at the site of nonunion where the ostectomy was performed.²⁵ Glenoid ostectomy offers advantages over arthrodesis of simplicity, maintenance of some degree of shoulder mobility, lower surgical costs, and no implant-associated complications because orthopedic implants are not used. In small animals, glenoid ostectomy has favorable, long-term results with return to pain-free function.^2,3

To the authors’ knowledge, the present case report is the first description of a shoulder joint luxation in an equid treated with glenoid ostectomy. This technique was chosen because shoulder joint arthrodesis was not an option for the owner. Glenoid ostectomy resulted in an acceptable postoperative outcome on the basis of patient comfort and function. On the basis of our experience with this technique, we believe glenoid ostectomy should be considered as a viable and affordable alternative to shoulder arthrodesis in small-breed equids. This technique required minimal postoperative care, no orthopedic implants, decreased anesthetic and operative times, and decreased soft tissue dissection during surgery and was not associated with any major complications. In this case, postoperative rehabilitation involved confinement for 2 months prior to turnout into larger areas to encourage walking and movement followed by unrestricted pasture turnout.

In regard to patient size, we are not able to make recommendations for how the technique would work for full-size horses, but it would be useful in small ponies and miniature horses and donkeys. To our knowledge there are no reports of substantial anatomic differences between donkey and horse anatomy that would affect the surgical procedure or outcome. We have concerns for contralateral limb laminitis in larger-sized horses because our patient was not immediately fully weight-bearing on the affected forelimb after surgery. Although we only have experience with a single case, glenoid ostectomy could be considered as an alternative to arthrodesis in small equids with chronic osteoarthritis or fractures affecting the shoulder joint. In summary, glenoid ostectomy is an acceptable alternative to shoulder joint arthrodesis in small equids with chronic luxation of the shoulder joint. It was associated with lower cost (compared with arthrodesis), a low rate of complications, and an acceptable postoperative outcome.