Introduction

Lameness attributable to shoulder problems is diagnosed much more frequently in dogs and cats in recent years. This increased prevalence may simply be due to improved diagnostic methods and a higher index of suspicion by veterinarians. This lecture will discuss a variety of shoulder problems including osteochondritis dissecans (OCD), glenoid fragmentation, biceps tendon problems, supraspinatus tendon injury, infraspinatus contracture and chronic osteoarthritis. Practical tips will be given to reach a diagnosis using gait evaluation, physical examination, radiographic examination and arthroscopic assessment. Treatment options and expected outcomes will also be addressed. Shoulder instability will be addressed in a separate lecture.

Osteochondritis Dissecans (OCD)

Osteochondritis dissecans is a manifestation of osteochondrosis in which a flap of cartilage is lifted from the articular surface. Osteochondrosis is thought to precede OCD and is a disturbance in endochondral ossification. The disturbance in endochondral ossification leads to multiple areas of cartilage islands on the surface and within the humeral epiphysis, which have not undergone normal maturation into bone. Areas of abnormal endochondral ossification of the articular surface become thickened and are susceptible to fissure and loosening (OCD) as the deeper chondrocytes undergo necrosis due to inadequate nutrition and a suboptimal microenvironment.

Large and giant-breed dogs are commonly affected and males are more often affected than females. Clinical signs often develop between 4 and 8 months of age; however, some dogs may not be presented for veterinary evaluation until they are mature. Affected animals are usually presented for examination because of unilateral forelimb lameness. Owners usually report a gradual onset of lameness that improves after rest and worsens after exercise.

On physical examination, the shoulder should be palpated and moved through a complete range of motion. Crepitation or palpable swelling of the joint is seldom evident, but affected animals usually exhibit pain when the shoulder is moved into hyperextension or extreme flexion. Often the examiner can detect muscle atrophy of the forelimb by loss of muscle mass adjacent to the spine of the scapula.

Despite apparent lameness in only one limb, both shoulders should be radiographed because this condition is often bilateral. Sedation may be required for quality radiographs, particularly in large, hyperactive dogs. The earliest radiographic sign of OCD is flattening of the caudal humeral head. This is due to thickening of the articular cartilage and deviation of the subchondral bone line. As the disease progresses, a saucer-shaped, radiolucent area in the caudal humeral head may be visualized. Calcification of the flap may allow visualization of the flap either in situ or within the joint if it has detached from the underlying bone. In chronic cases, large calcified joint mice are often observed in the caudoventral joint pouch or cranially within the bicipital groove.

Surgery is the treatment of choice. The tenets of surgical treatment include removal of the cartilage flap and treatment of the subchondral bed. The edges of the OCD lesion should be carefully probed to ensure complete removal if abnormal cartilage. The edge of the lesion should also be debrided with a curette so that the cartilage edge is perpendicular to the subchondral bone. The subchondral bed is treated by abrasion arthroplasty or curettage to remove necrotic bone or cartilage. Microfracture or forage can also be performed to encourage influx of mesenchymal cells and fibrocartilage repair. Arthrotomy or arthroscopy can be used for surgical treatment. Arthroscopic treatment is highly recommended due to the lower patient morbidity, improved visualization and increased precision in treatment. Arthroscopic treatment also allows treatment of both shoulders at the same sitting if the condition is bilateral. Activity should be restricted to leash walk for 4 weeks following surgery.

Glenoid Fragmentation

Fragmentation of the caudal edge of the glenoid can lead to chronic shoulder pain and lameness in some dogs and cats. The condition can also be asymptomatic and seen as an incidental finding. This syndrome may represent a secondary center of ossification or a traumatic injury. Clinical signs include pain on manipulation of the shoulder, forelimb lameness and atrophy of the shoulder muscles as the condition becomes chronic. Conservative treatment with rest, physical therapy modalities and pain management can be attempted initially. Shock wave therapy may also be beneficial in some patients. Surgical treatment is recommended in patients that do not respond to conservative treatment. Arthroscopic treatment is preferred to arthrotomy due to lower patient morbidity and increased precision of treatment. Treatment includes removal of the osteochondral fragment and debridement of the subchondral bed with a curette, burr or motorized shaver. Activity should be restricted to leash walk for 4 weeks following surgery. Arthroscopic evaluation reveals an unstable, mobile fragment in most symptomatic patients. Conversely, stable, non-displaced fragments are typically seen in asymptomatic patients. Most patients return to normal function; however, some require long-term pain management if the lesion is large or if concomitant osteoarthritis is present.

Biceps Tendon Injury

Arthroscopy is the preferred method of evaluation of the biceps tendon and cranial joint compartment in the dog and cat. Arthroscopy is minimally invasive, yet allows thorough evaluation of the supraglenoid tuberosity, biceps tendon and tendon sheath. In addition, a complete evaluation of the medial, caudal and lateral joint compartments can be accomplished at the same time. A lateral scope portal and a cranial instrument portal are used. Biceps tendon abnormalities are more commonly diagnosed today due to the availability of arthroscopy. The normal biceps tendon has a smooth, white surface with a small amount of vascularity at its origin. Bicipital tenosynovitis was once the most common injury to the biceps diagnosed, but this diagnosis was often made based on history, clinical signs and arthrography. Definitive diagnosis was usually not made based on direct visualization or histopathology. This diagnosis is made much less frequently now, because many of these patients have been found to have partial or complete tears of the biceps tendon. Arthroscopy provides a quick and noninvasive method of diagnosing partial biceps tendon tears or complete biceps tendon tears. Radiographic changes are usually limited to calcification of the origin of the biceps tendon near its origin at the supraglenoid tuberosity in chronic cases. This area of calcification must be differentiated from that seen with supraspinatus mineralization. Treatment of the biceps tendon can also be accomplished in some cases under arthroscopic assistance. Biceps tendon release is a recommended and easily performed procedure accomplished using a radiofrequency probe or scalpel blade. Activity should be restricted to leash walk for 4 weeks following surgery. Most dogs return to normal function, but occasionally a mile intermittent lameness may be seen long term. Arthroscopic-assisted biceps tenodesis is also possible, but is technically more demanding. The surgeon must be cautious not to over-interpret changes seen, as generalized inflammation within the joint, such as occurs with OCD, may lead to hypervascularity and synovial proliferation at the origin of the biceps tendon. Removal of the OCD flap leads to resolution of these changes in the tendon.

Supraspinatus Injury

Tears of the supraspinatus tendon can be acute or chronic. Chronic tears are most commonly diagnosed. Patients may exhibit pain on direct palpation of the insertion of the supraspinatus tendon on the greater tubercle of the humerus. Pain may also be evident with flexion of the shoulder. Chronic intermittent or persistent forelimb lameness may be seen. Acute tears may have subtle, soft tissue swelling or bruising. Chronic tears may be associated with muscle atrophy. Radiographic changes are usually limited to calcification of the supraspinatus tendon near its insertion in chronic cases. This area of calcification must be differentiated from that seen with biceps tendon mineralization. It is also important to point out that mineralization may be asymptomatic; therefore, it is important to demonstrate shoulder pain prior to treating this condition. Ultrasound examination is also useful to assess for injury to the tendon or muscle belly of the supraspinatus. Other conditions such as elbow dysplasia, shoulder instability, biceps tendon injury and shoulder OCD should be ruled out. Conservative treatment with rest, physical therapy modalities and pain management can be attempted initially. Shock wave therapy may also be beneficial in some patients. Surgical treatment is recommended in patients that do not respond to conservative treatment. Surgical treatment options include debridement of the damaged, calcified region of the tendon or, tendon reattachment or tendon transection and reattachment in a nearby area, being sure to reduce the amount of tension on the tendon. Tendon release without reattachment is not recommended due to the great degree of stability provided to the shoulder by this important tendon. Activity should be restricted to leash walk for 8 weeks following surgery. Prognosis is good to excellent in most patients. Some patients require long-term pain management due to persistent lameness.

Infraspinatus Muscle Injury

Tears of the infraspinatus can be acute or chronic. Acute tears may have subtle, soft tissue swelling or bruising. Obvious forelimb lameness is observed. Occasionally, muscle necrosis can occur secondary to a compartment syndrome after acute trauma. Patients may exhibit pain on direct palpation of the muscle belly of the supraspinatus tendon on the greater tubercle of the humerus. Pain may also be evident with flexion of the shoulder. Diagnosis is made by physical examination and ultrasound examination. Conservative treatment is often successful. Treatment options include activity restriction, hypothermia therapy, ultrasound therapy and pain management. If a compartment syndrome is suspected, surgical release of the deep fascia is recommended.

Chronic tears are most commonly diagnosed. Chronic intermittent or persistent forelimb lameness may be seen. Chronic tears may be associated with muscle atrophy and fibrosis, resulting in infraspinatus contracture. Shortening of the muscle causes a characteristic forelimb gait characterized by external rotation, abduction and circumduction of the limb during ambulation. Surgical treatment is recommended. Transection of the tendon of insertion of the infraspinatus provides quick resolution to the abnormal gait in almost all patients. Activity should be restricted to leash walk for 2 weeks following surgery. Long-term prognosis is excellent.