Hock problems in mature horses often stem from wear and tear. But young horses can get sore hocks, too--sometimes before they're fully into work. Defects in bone development can lead to two conditions:
Bones form from cartilage that gradually mineralizes, becoming hard. A layer of cartilage remains at bone ends to provide a slick working surface for joints. But sometimes the process is incomplete, leaving cartilage under this layer. Lesions form, and a fragment of cartilage or bone may break away, a condition called osteochondritis dissecans (OCD). When these lesions form in the hock, they're typically in the upper part, most often on the ridge of the tibia. Upright conformation and fast growth are linked to OCD; there may be genetic factors as well.
Often the problem doesn't show up until the horse begins work. Then he develops "boggy" (soft) swellings on the front or the inside aspects of the hock, as fluid builds up in the joint capsule. He may or may not be lame.
Swelling often goes down with rest. If the lesion is small, the horse isn't lame and he's not slated for a performance career, you may decide to leave it at that. But because the problem can continue to flare up and cause more problems down the road, surgery to remove fragments and smooth rough surfaces is often the treatment of choice. This is usually done with an arthroscope--a tubelike instrument with optical fibers and lenses, inserted into the joint through a tiny incision. The outlook is good, especially if the problem doesn't affect a large area of the joint.
A different defect can lead to serious problems in the lower hock joints of young horses. In this case, the small distal (lower) hock bones (sometimes called cuboidal bones) don't form properly, leading to early arthritis. Sometimes the defect is bad enough that the youngster develops a crooked leg. There isn't much that can be done in these cases. If the bones aren't greatly malformed, however, it may be possible to surgically fuse the joint.
To learn more about hock health and the latest treatment options and preventives, see "Combat Hock Wear and Tear" in the June 2008 issue of Practical Horseman magazine.