Osteochondritis dissecans (OCD) is a common type of developmental orthopedic disease (DOD)
of horses that affects the articular (joint) cartilage, and often may also involve the subchondral bone just beneath the cartilage surface. Usually only one of the horse's joints are involved, with bilateral involvement (in which both hock joints, or both stifle joints, etc. are affected). It is less common for horses to have multiple joints involved (such as both
the hock and stifle joints). The associated signs, treatment, and prognosis of OCD depends on the joints that are affected.
OCD of the Stifle joint
Horses are most commonly affected by OCD of the stifle (femoropatellar) joint. Approximately 60% of horses that are affected by this condition are one year of age or less at the time signs develop in affected horses. Horses with OCD of the stifle joint often have a history of a recent increase in the level of athletic fitness training. The typical signs are a sudden onset of joint swelling and mild lameness. Lameness is usually associated with a shortened stride and stiff leg action. When horses are more severely affected, they may develop a 'bunny hop-like' gait which can sometimes confuse owners into thinking that the horse has a neurological problem. Thoroughbreds are most frequently affected by OCD of the stifle joint.
OCD of the Hock joint
OCD of the hock (tarsocrural) joint is most commonly seen in Standardbreds, although all breeds can be affected. Clinical signs of this condition manifest as Bog spavin
, which is a prominent swelling that develops along the inner part of the horse's hock joint. Lameness may also be present in some horses, however it is usually mild. Although lameness may only be mild initially, if the condition goes untreated, it often becomes a problem later in life which limits their ability to perform at upper levels or at racing speeds. Surgery early in the horse's life is considered the best treatment, and is associated with the most positive prognosis. Once degenerative changes begin to occur, as a result of the lesions, the prognosis for the horse decreases with respect to their athletic career.
OCD of the Shoulder Joint
The shoulder joint is one of the least common joints affected by OCD in horses, however when it does occur it is the most debilitating type of OCD. This is because it often involves a large portion of the joint surface, and accompanied often by secondary joint disease. Signs usually develop in horses when they are about one year of age or younger. These horses will usually have a history of forelimb lameness, sometimes with muscle atrophy. Because horses will modify their gait as a result of the pain, they often develop uneven feet, with one foot appearing club-footed, and the foot may look smaller then the other. Any pressure exerted in the shoulder area will cause the horse discomfort. The changes of a favorable outcome for horses to perform well athletically with OCD of the shoulder joint is quite low, however the chances improve if the horse has had surgery early on, when the signs first present.