The hock is the joint that is about half way down the back leg and most closely resembles the bent elbow of a human. The hock is the joint that gives the horse thrust by straightening out the leg either for forward or upward movement. Since the weight of the horse in turns and forward and upward movements is on the hock, good conformation is essential to ensure that the joint will stay strong and solid throughout the horse's life.
There are several different conformation problems that can occur, most which are congenital or are present from birth. One problem is hocks that are too straight, which is known as post legged. These horses have little thrust and often have poor pastern positioning, resulting in joint and foot problems as the horse ages.
Sickle hocks are the opposite problem to a post legged horse. A horse with sickle hocks has too much bend in the hock, leading to a bowed shape in the lower leg rather than the correct conformation. In severe cases of sickle-hock the horse appears to be pulling the bottom of the leg, known as the cannon bone, up and under the body.
Horses with sickle hocks are more likely to develop hind leg problems as they mature and are worked. Many horses with sickle hocks will develop conditions such as bog spavin, curb and throughpin. These horses may have difficulty with the hind legs seeming to catch or lock when they are in certain gaits, the trot is particularly problematic for horses with this conformation.
Curb is a condition that is noted by a lump that forms on the back of the hind leg about three to four inches down from the hock. Curb is a temporary swelling that is not problematic to the horse provided he or she is rested and provided time for the swelling to go down. The lump is caused by the wear and tear on the ligament due to the backward pressure on the hock from the angle of the cannon bone.
Bog spavin is a similar soft swelling in the area around the hock but it is more commonly found to be on the inside and front of the joint. Like curb, bog spavin can be treated with rest, anti-inflammatories and careful monitoring of the amount of exercise the horse is provided. Corrective shoes that help to change the angle of the feet can be somewhat helpful, depending on the degree of conformation problems.
Throughpin is a swelling at the top of the hock that, like curb and bog spavin is soft to the touch and will not usually cause any permanent lameness if treated with rest and anti-inflammatories.
Bone spavin is a serious, painful condition that will cause permanent lameness in sickle-hocked horses. This is a hard, bony growth that develops due to injury to the hock joint in movement. Typically these horses will lose flexibility in the back legs and movement will be very painful. Pain management and injections of corticosteriods can often be helpful, however is severe cases the horse may never gain full range of motion.