Equine Osteochondritis Dissecans (OCD): What is it all about?
by Dr. Tessa Lumley
Osteochondritis Dissecans (OCD) is a common developmental orthopedic disease that affects the cartilage and subchondral bone of growing horses. OCD may affect up to 25% of the overall horse population, and can occur in all breeds of horses. However, the breeds most commonly affected include Warmbloods, Standardbreds, and Quarter Horses. In growing equids affected by OCD, there is a problem with the normal process in which cartilage is made into bone through a process called endochondral ossification. This defect in bone formation leads to retention of thicker pieces of cartilage that is inherently weaker; this can cause lesions that dissect down to the joint surface. These lesions often manifest as cartilage or bone flaps that may either remain connected to the parent bone or break off and float around the joint itself. These OCD fragments or flaps cause an influx in inflammatory proteins and debris into the joint causing generalized synovitis, or joint inflammation.
While a single underlying cause for OCD has not yet been identified, there are several factors that are credited with playing a contributing role in the pathogenesis of the disease. These include: Rapid growth and large body size, nutritional factors such as diets high in energy or an imbalance of trace minerals, genetic factors, imbalances in hormones such as insulin or thyroid, and traumatic events or routine exercise that result in a loosening of the OCD fragment.
While it is possible that horses affected with OCD may never go on to develop clinical signs, most will start to show evidence of disease in the first few years of life, especially as they are just starting into work. The most common clinical sign seen in horses with OCD is joint effusion—an increase in synovial fluid within the joint as a response to inflammation. Lameness is also commonly seen in horses with OCD though it may be very subtle and often only appreciated at higher speeds during exercise for racehorses or higher levels of training for other performance horses.
OCD lesions can occur in almost every joint, though they are most typically seen in the hocks, stifles, and fetlocks of horses. Diagnosis is made from radiographs and may be picked up during a lameness evaluation or incidentally during a routine pre-purchase exam. Bilateral lesions are common so if a lesion is observed in one joint, it is important to radiograph the opposite joint to determine the extent of disease. Additionally, it is possible but rare to find OCD lesions in more than one type of joint in the same horse, i.e., in both hocks and stifles, or hocks and fetlocks.
The most common form of treatment for OCD is arthroscopic removal of the bone fragment under general anesthesia. This surgical procedure involves making two or more small incisions into the joint, and using a small camera and other specialized instruments, the bone fragments are removed and the articular surface is debrided and smoothed. Recovery from surgery is often simple and straightforward, usually requiring a period of stall rest prior to starting back gradually into work. Post-operative bandaging and anti-inflammatory medications are also commonly indicated. While not all OCD lesions require surgical removal, prognosis for return to full athletic function is good to excellent for horses with surgically removed OCD lesions. If left in place the prognosis for athletic soundness goes down as the horse remains at greater risk for developing arthritis over time. For show horses, the swollen joint (effusion) will also resolve much more readily if the fragment is removed.
If you have any questions regarding this article or the health of your horse, please contact your veterinarian or the doctors at New EnglandEquineMedical & SurgicalCenter.
Tessa Lumley, DVM
New England Equine Medical & Surgical Center, 15 Members Way, Dover, NH 03820