Shoulder Osteochondritis Dissecans (OCD)

Endochondral ossification is the formation of bone from a cartilage precursor. Osteochondrosis (OC), a complex disease with genetic and nutritional etiology, is the failure of normal endochondral ossification. OC causes thickening of the articular cartilage such that focal necrosis develops in the deepest layers where nutrients from the synovial fluid fail to diffuse. Shearing forces may create a horizontal cleft in this pathologic cartilage. If a vertical cleft penetrates the articular cartilage surface, it is called osteochondritis dissecans (OCD). Exposure of the cartilage lesion to synovial fluid elicits synovitis and is thought to initiate lameness. It is worth noting that the thickened OC cartilage may cause radiographic subchondral flattening in a pup that fails to develop symptomatic OCD. Healing at this stage by endochondral ossification is still feasible. If healing fails at this stage, a mobile flap begins to form as the vertical cleft expands. The flap undergoes dystrophic calcification and may stay in place or become partially or completely dislodged; healingofthelesionatthisstageisnotfeasible.A“kissing” lesion of the adjacent articular surface is common. In the shoulder, all or portions of the flap may break off. In the shoulder, these fragments, called joint mice, may migrate to the caudal joint pouch or the bicipital tendon sheath. They may float free or become attached to the synovium. Often these joint mice grow gradually over time and it is not unusual to find multiple, large joint mice, marked synovitis, and end-stage osteoarthritis in adult dogs that went untreated as puppies.

Signalment
OCD of the shoulder most commonly affects male dogs of large breeds. Dogs typically present as puppies (4-8 months of age) for evaluation of lameness. The lameness is often most evident after intense activity. In some instances, the lameness is subtle enough to escape owner recognition or concern only to require veterinary attention when the dog reaches young adulthood (2-4 years of age). Radiographic OCD lesions affect both shoulders in 27-68% of cases. Gait evaluation and physical examination are carefully performed to determine if both shoulders are symptomatically affected, particularly if arthroscopic treatment is not feasible. When dogs are severely lame on one limb, close scrutiny is required to detect lameness in the opposite limb. Often the lameness is most easily evaluated at a walking gait where shortening of the stride is noted. Slowly descending stairs can also be helpful because dogs typically lead with the more comfortable limb, but may be very hesitant when both shoulders are painful.
Palpation often reveals prominence of the acromial process due to atrophy of the spinatus and deltoid muscles. Pain is detected upon shoulder extension and rotation. Crepitus is seldom detected. [...]