Developmental orthopedic disease is a term used to describe problems that develop in the bones of growing horses, and there are several different syndromes. A paper in Horse.com by several specialists have covered the subject well starting with osteochondrosis. Osteochondrosis involves two conditions-osteochondritis dessicans and subchondral bone cysts and both of these affect the joints. Some horses are genetically predisposed to developing these problems while in others the cause is related to rapid growth and nutrition as well as trauma to the joints. You can see that genetics, rapid growth, and nutrition are all tied together as a cause because some of these foals are genetically programmed to grow rapidly and excessive nutrition just adds to the opportunity of rapid growth.

As far as trauma, Dr. Michael Schramme from North Carolina State indicates it is better to provide foals with free turnout rather than confine them and give them short bursts of high speed activity. He indicates foals that have not had free turnout by five months of age do not have cartilage that can adapt to the load placed on it. Osteochondritis dessicans, or OCD, occurs when the surface of the joint does not change from cartilage to bone as the foal grows and cartilage remains. This cartilage can become dislodged and cause lameness and later arthritis if not repaired. The joints most commonly affected by OCD include the stifles, hocks, and fetlocks and commonly both legs are affected. Sixty percent of the cases diagnosed are in horses less than one year of age, and some cases have mild lameness with only swelling of the affected joint.

Diagnosing OCD can be difficult because although many cases can be diagnosed with x-rays, the OCD lesions do not always show up on x-ray. Also, the disease commonly occurs in both joints so if it is in one leg in a certain joint, the other leg should always be checked. Dr. Wayne McIlwraith from Colorado State indicates that diagnosing some of these cases requires placing a scope in the joint and looking at the joint surface. Treatment of most OCD lesions requires surgery that can also be performed with a scope; this prevents the need for a large incision as the surgery can be performed through two little holes. Some horses with small lesions may respond to rest and may not require surgery, but you always run the risk of arthritis developing later in these joints.

Another related problem in young horses is the subchondral bone cyst. A sac-like cavity forms in the bone just below the joint surface and is usually noted as a cause of lameness in horses less than three years old. Treatment of these cysts is controversial as some believe surgery is required while others have had success injecting the cysts with cortisone and other medications.