Shoulder osteochondrosis

What it is

Osteochondrosis is a failure of endochondral ossification in the growing articular-epiphyseal cartilage. The cartilage stays abnormally thick, its deep layers are poorly nourished and become necrotic, and a fissure separates a flap of cartilage from the subchondral bone. Once a flap forms and the joint becomes inflamed, the condition is called osteochondritis dissecans (OCD). The flap may stay attached, or detach and become a "joint mouse" that can migrate into the bicipital tendon sheath. The cause is multifactorial: genetics, rapid growth, excess energy and calcium in the diet, and local mechanical stress.

Who it affects

Young dogs of large and giant breeds, usually between 4 and 10 months of age: Great Dane, Labrador and golden retriever, Bernese mountain dog, Rottweiler, Border collie, Newfoundland. It is more common in males and is frequently bilateral, even when lameness is seen in only one limb. The shoulder is the joint most often affected by OCD in the dog, followed by the elbow, stifle and tarsus.

Anatomy involved

The lesion sits on the caudal or caudocentral part of the humeral head (caput humeri), the area that bears the most load against the glenoid cavity of the scapula (cavitas glenoidalis) when the dog stands. A "kissing lesion" of the opposite glenoid cartilage may develop. Free fragments tend to lodge in the caudal joint pouch or in the sheath of the tendon of origin of the biceps brachii, which communicates with the shoulder joint.

Clinical signs

Gradual onset of mild to moderate thoracic limb lameness that is worse after rest or heavy exercise. Pain on full extension and flexion of the shoulder is the key finding; atrophy of the supraspinatus and infraspinatus muscles may develop with time. Joint effusion is hard to palpate in the shoulder.

Diagnosis

• Radiographs: mediolateral views of both shoulders, with the limb pulled forward and the other one pulled back so the humeral heads do not overlap. Flattening or a concave defect of the caudal humeral head with sclerosis of the subchondral bone; a mineralised flap or free body may be seen. Screen the opposite shoulder.
• Arthrography, CT or arthroscopy to show a cartilage flap that is not mineralised.

Treatment

Small lesions without a flap may heal with rest and controlled exercise. Once a flap is present, the treatment of choice is its removal and curettage of the bed of the lesion, by arthroscopy or arthrotomy; fibrocartilage then fills the defect. Joint mice in the bicipital sheath should be removed. Prognosis after surgery is good, and much better than for OCD in the elbow, stifle or hock. Avoiding overfeeding and excess calcium in growing large-breed puppies reduces the risk.