Osteochondrosis is a condition associated with defective development of bone from cartilage resulting in inflammation in affected joints. Often loose fragments of cartilage and/or bone present in joint, usually stifle, hock, fetlock, shoulder. Osteochondrosis occurs particularly in young, rapidly growing individuals. There is probably a genetic predisposition in foals. Encouraging a horse to grow quickly using high planes of nutrition may increase the risk of the disease. The stifle and hock are most commonly affected in the hind leg and the shoulder joint in the front leg. The clinical signes are usually evident in the first two years of life. Most common signs are include joint swelling and lameness.
During development of bone, cartilage is converted to bone. Impaired blood supply to the cartilage will delay conversion of the cartilage to bone and result in abnormally thick cartilage on the joint surfaces, the lower layers of which may die. THerefore the cartilage on the joint surface is only loosely attached to the underlying bone and may become detached. This causes inflammation within the joint and production of excess synovial fluid, with the result that the joint capsule becomes distended. Although some joints may have mild osteochondrosis without clinical signs, the majority of lesions cause lameness and deteriorate if not treated.
Diagnosis is based on clinical signs and is confirmed by a combination of physical examination, scintigraphy, and radiography. Arthroscopy (examination with a camera inserted into the joint through a small incision of about 1/2 inch) can be used to confirm the diagnosis and treat cartilage and subchondral bone lesions. The disease often affects both stifles, so it is important to take radiographs of both joints even if only one is obviously affected. Treatment is by surgery. Abnormal cartilage is stripped off the underlying bone and the bone is scraped until healthy bleeding bone is exposed. Young and middle-aged horses with mild osteochondral lesions of the shoulder joints have a good prognosis for return to performance following arthroscopic treatment.