Subchondral Cystic Lesions
Subchondral cystic lesions are areas within bone where there is a loss of bone density within the bone, underneath the cartilage. There are a couple of theories as to how they develop, either as part of the osteochondrosis process (e.g. OCD bone chips) or as a result of trauma to the cartilage and then hydraulic action of the joint fluid. Generally, they form when the horse is young, however may lay dormant for a long time. The prognosis for the horse is also better when the horse is treated while young, before any other joint disease can occur such as arthritis as a result of the joint disease.
The most common site for them to form is the medial femoral condyle, within the stifle. Other common locations include the elbow, fetlock, coffin bone and pastern. They can cause anything from intermittent mild to fairly severe lameness and are diagnosed primarily with radiographs, but also with advanced imaging techniques such as CT and MRI. Proving that the cyst is the cause of lameness is challenging as the cysts don’t always have a large opening into the joint, so blocking the joint with local anaesthetic may not block the cyst.
The current gold standard treatment is to place a screw across the cyst and the best way to do this in the stifle is under arthroscopic guidance, which is a newer technique described in 2023. These are not something that is seen that commonly, however Andrew recently performed 3 of these surgeries in a 10-day time period!
The screw changes the biomechanics of load going through the leg and stimulates bone formation within the cyst. Young racehorses that get the surgery can return to racing and the screw is associated with better reduction in size of the cyst and quicker convalescence period compared with alternative techniques. The screw technique has been shown to improve lameness and the prognosis is generally 70-75% for improvement of lameness and radiographic resolution of the cyst.
If you have a horse with a subchondral cystic lesion, please contact Andrew at Endell Equine Hospital to discuss the case on 01722 710046.
