Of these four joints, it is very often the hock joint that is the most stressed. There are two conformational flaws that add stress to the hock joint, and four conditions that you should be aware of. The conformational flaw referred to as, "Sickle Hocked" means that the imaginary line drawn down from the horse's buttocks hits on the back of the hock correctly, but from the hock down the leg is angled up under the horse. In horses that are bred to perform quick stops and turns such as reining, roping and cutting horses, a mild degree of sickle hocked is not uncommon. "Cow Hocked," is a conformational flaw that can be seen by standing directly behind the horse. The hocks on this type of horse turn inward.
Unsoundnesses and blemishes of the hock include "Capped Hock," "Thoroughpin," "Bog Spavin," and "Bone Spavin." Of these, bone spavin is the most serious and only true unsoundness, though temporary lameness may also accompany the other conditions. Bone spavins are most closely linked to the stress caused by the conformational flaws of being cow hocked or sickle hocked. Another contributing factor is how hard the horse is worked. It is most common in horses that are ridden hard at a gallop. Bone spavins are a result of damage to the cartilage around the hock which progresses to degenerative arthritis. If it has been present for a long time, you will see a bony enlargement on the inside of the leg just below the actual hock joint. This enlargement is called a "Jack." Bone spavins are sometimes referred to as "Jack Spavins" also. The degenerative process begins long before the spavin appears. If a horse shows signs of lameness when he is first brought out to work, then becomes sound during the workout and the lameness returns again later on, x-rays should be taken of the horse's hocks.
Capped hocks, bog spavins and thoroughpins are all types of swelling in the hock joint that can usually be successfully treated, putting them in the category of blemishes. A capped hock is a swelling on the knobby exterior part of the hock on the very back of the leg. It is usually caused by repeated blows. A similar condition may exist on the elbow in the front leg (where the leg meets the body on the back of the front leg.) A thoroughpin is a swelling inside the thinnest part of the hock joint. Sometimes you can push the thoroughpin from one side to the other. A bog spavin can be distinguished from a thoroughpin by the fact that there are actually three areas of swelling. The swellings will occur on either side and on the front of the hock joint.
