Clunking Hocks

Q. I have two differently-bred Miniature Horses, one yearling and one weanling, and both have a horrible clunking sound that definitely comes from their hocks. I only hear it when they walk, never at the trot or canter.

Some people have told me it is their growth plates and they will grow out of it, but I am not completely satisfied with that answer and have been trying to find someone that has experienced this same problem who can give me some better reason. Can you explain what this condition is and if it can be treated?

Tina, Australia

A. Both of the horses that you describe are young, and this is probably why the growth plates were suggested as being a potential cause. However, this is not likely to be the source of the noise. With the fact that this noise is identified when the horse walks, I would suspect that they are suffering from intermittent upward fixation of the patella. This condition is often associated with an audible snap whenever the patella releases from the medial trochlear ridge of the femur, and it usually occurs when the horse moves from rest or standing, rather than when the horse is already in motion. The hind leg is in stiff extension with the fetlock flexed, and once it "pops," the leg is freed up and can flex normally again.

This problem is usually seen in immature horses, and the majority will grow out of it as they mature or develop better conditioning. As long as the upward fixation is intermittent, improving the horse's level of conditioning and increasing the amount of turnout is often all that is required.

From your lack of description of any lameness, I'm assuming that none is present. If any is identified, a veterinarian should examine the horses to ensure there is no other injury that could be contributing to the problem. If the upward fixation becomes persistent, or it cannot be easily relieved either by the horse itself or by human intervention (walking the horse backwards or attempting to flex the fetlock and hock manually), surgical options are available. Transecting (cutting) the medial patellar ligament can prevent this from recurring, but if the patient is not strictly confined following surgery, patellar fractures and arthritis can develop secondarily to the joint instability that this surgery creates. Another surgical option (and the safest) is medial patellar ligament splitting. This does not have the same complications or risks as the transection, but it will not free up the patella immediately (it should occur within a day or two). If you want to try something other than surgery, injection of irritants into the patellar ligaments can also sometimes help limit this condition.

About the Author

Colin Mitchell, BVM&S, MS

Colin Mitchell, BVM&S, MS, is an associate professor of equine surgery in the Department of Veterinary Clinical Sciences at Louisiana State University.

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