A capped hock is a swelling of the capsule around the hock, often caused by the horse kicking the stall wall. In some cases, the swelling can become permanent, but it generally doesn't cause lameness. Surgery is sometimes performed in show horses (judges care about these things). Cold hosing is the general treatment for a new injury, and if that doesn't work they might drain it to reduce the swelling. Elbows (the joint at the top and the back of the foreleg) can also end up capped.