“Osteochondrosis is a disease in which the cartilage at the end of long bones, such as bones in the leg, fails to develop normally,” says Annette McCoy, DVM, PhD, Dipl. ACVS, an equine surgeon at the University of Illinois Veterinary Teaching Hospital in Urbana. “Sometimes this disease results in a fragment of bone or cartilage breaking off on the surface of the joint, and that problem is known as osteochondritis dissecans.”

Up to 80% of young horses in some breeds develop osteochondritis dissecans, McCoy says. Although any breed of horse can be affected, Standardbreds and Warmbloods are considered to be predisposed to osteochondritis dissecans.

Any joint can be affected. The joints most commonly affected in horses are the fetlock, hock, and stifle. It is not uncommon to have bilateral disease, meaning in the same joint is affected in both the right and left legs. It is less common, however, to have multiple joints in the same leg affected.

Risk Factors for Disease

What factors contribute to the risk of developing osteochondrosis is the subject of McCoy’s research. Environment (including such factors as diet, exercise, and biomechanics) and genetics each play a role in disease development. McCoy is conducting a study that examines how biomechanical differences in gait—pacing vs. trotting—could interact with genetic traits to affect Standardbreds’ risk of developing osteochondrosis