Osteochondritis dissecans (OCD) is a relatively common developmental disease that affects the cartilage and bone in the joints of horses. It causes clinical signs of disease in 5-25% of all horses and can occur in all horse breeds. Cartilage in joints with OCD doesn’t form normally; this causes the cartilage and bone underneath it to become irregular in thickness and weaker than in normal joints. This can cause the development of cartilage and bone flaps that can either remain partially attached to the bone or break off and float around in the joint. These loose flaps and areas of abnormal cartilage and bone cause inflammation in the joint and over time may lead to the development of arthritis. OCD is usually caused by a combination of several factors acting together, including:
- Rapid growth and large body size
- Nutrition: Diets very high in energy or have an imbalance in trace minerals (low copper diets)
- Genetics: Risk of OCD may be partially inherited
- Hormonal imbalances: Insulin and thyroid hormones
- Trauma and exercise: Trauma (including routine exercise) is often involved in the formation and loosening of the OCD flap
The most common sign is effusion (swelling) in the joint of a young horse (Figure 1). Signs can be seen as early as 5 months of age, but may not occur until the horse is started into work. Lameness varies with location and severity of the OCD; most horses are sound at a walk but may display lameness at faster speeds or when put into work. OCDs can occur in virtually all joints, but they occur most frequently in the hock, stifle and fetlock joints.
Horses with severe lameness and joint swelling probably have a more serious problem and should be examined on an emergency basis. If your horse has a swollen joint it should be examined by your primary care veterinarian in order to diagnose OCD and to rule out other causes. Your veterinarian will probably want to do the following diagnostics:
- Physical Exam
- Lameness Exam
- Radiographs (Figure 2)
OCD is often bilateral and radiographs of the opposite joint should be taken, even if there is little or no swelling in that joint. Occasionally an OCD fragment is made entirely of cartilage (no bone) and so it can’t be seen on the radiograph; only a defect in the main bone may be seen in these cases. Sometimes older horses are diagnosed with OCD incidentally without apparent clinical signs.
Aftercare recommendations depend on the location and severity of the OCD but typically involve a period of stall rest followed by progressive exercise. Full return to training may require several months. Postoperative bandaging will be required for some OCD locations and medication may be prescribed, including anti-inflammatory medications. A follow-up examination and suture removal may also be required. Specific recommendations on aftercare will be made by the veterinary surgeon for each case.
Prognosis for athletic function is good to excellent for most OCDs that are treated surgically. Some OCD locations, such as the shoulder, may have a reduced prognosis. In general, if the OCD lesion is not removed the prognosis for future soundness will be decreased. It is important to discuss the expected outcome, including appearance of the operated joint, with the veterinary surgeon during treatment selection.