OCD is short for Osteochondritis Dissecans, a developmental disorder of the bones and joints that is somewhat common and may affect any breed of horse. The condition may also be referred to as an OCD lesion or an OCD fragment after radiographic evaluation of the affected joint. It is thought to be an inherited problem, although other factors are shown to contribute to the risk of developing symptoms of advanced joint disease. These include abnormally rapid growth spurts while bone and articular cartilage is not yet fully developed, diets that may contribute to rapid growth, mineral deficiency, and certain hormone imbalances. OCD is likely to be painful and left untreated may become eventually crippling.
After a foal is born, its bones and joints are still not completely developed. This is to allow for growth until the horse reaches its full stature at about three years of age. The ends of the bones adjacent to the animal’s various joints continue a process called endochondral ossification which produces the cartilage, or padding between the bones in the joint, and the hardened smooth surfaces that cap the ends of the bone. An interruption in this process leads to irregularly shaped, weakened cartilage and bone surfaces leading to instability, decreased range of motion, and a propensity to develop fractures within the joints.
OCD is one such “interruption” in joint development. The term literally means a separating (dissec-) section of bone (osteo-) and cartilage (chondro-) caused by inflammation (-itis). Inadequate blood supply to malformed articular tissues leads to necrosis, or tissue death, and eventual separation from their normal anatomical positions. Partially attached flaps and free floating fragments cause pain and further inflammation in the joint when the pieces impede normal joint movement and cause injury to healthy cartilage. Exercise or trauma to the affected joint will accelerate this process of fragmenting and articular damage. The abnormal joint will develop arthritic changes at an increased rate causing swelling and debilitation at a young age.
OCD lesions may cause symptoms of lameness at a few months of age or remain undetected until adulthood. The disease is usually confirmed by taking x-rays at about 12 months old. It is difficult to assess how many horses will become symptomatic from OCD lesions, but between 25 and 60 percent of horses show radiographic joint abnormalities on pre-purchase exams. Progressing disease will often result in joints swollen with effusions (inflammatory joint fluid). Swelling may suddenly occur after an exercise regimen is begun (i.e., formal training program).
Lesions may occur in any of the joints of the limbs, with the hocks, fetlocks, and stifles being most commonly affected. A diagnosis of OCD usually requires surgical intervention to remove the abnormal tissues and fragments. An arthroscopic procedure (performed by a surgical specialist) is preferred to an open surgery to avoid the risk of joint infections post-operatively. Healing times are quicker after this less invasive method as well, because the incisions through the skin and joint capsule are smaller. Surgery will require general anesthesia, so preliminary blood work will be assessed to minimize the risk to the patient. An arthroscope is a thin flexible tube with a lens or a tiny camera attached to the end that is inserted through one incision to visualize the internal joint anatomy and guide other instruments through another small incision in order to remove OCD fragments.
The horse will be rested for a period of time after surgery depending upon the complexity and location of the surgery. Low-impact physical therapy will follow according to the surgeon’s recommendations. Full recovery will usually take several months. Often, the surgical site will require bandaging for a week or two to minimize post-operative swelling and protect the incisions from contamination. Also, non-steroidal anti-inflammatory drugs (NSAIDs) for pain relief, and antibiotics to prevent bacterial infection, are typically prescribed to horses undergoing OCD surgery.
Most horses that are treated early in the onset of OCD of the distal (lower) limb joints have a good long-term outlook. OCD lesions in the shoulders carry a more guarded prognosis. This depends upon the owner’s diligent adherence to rehabilitation recommendations from the veterinarian.
Osteochondritis Dissecans is strongly suspected of being hereditary. Careful breeding may indeed reduce its prevalence in subsequent generations of horses. The trouble is that so many horses may show evidence of joint abnormalities on screening x-rays without ever exhibiting clinical symptoms attributed to OCD. Until a stronger association can be made, controlling the other factors that contribute to the development of OCD lameness is the most reasonable prophylactic effort at this point. Preventing excessively rapid growth during development is vital. A veterinarian can help the horse owner determine an appropriate diet and mineral supplement, if deemed necessary, most beneficial to growing foals.