Osselet

Osselet is arthritis in the fetlock joint of a horse.

Location

Osselets usually occurs in the front legs of the horse, because there is more strain and concussion on the fetlock there than in the hind legs. The arthritis will occur at the joint between the cannon bone and large pastern bone, at the front of the fetlock.

Causes and Progression

Osselets is caused by stress on the fetlock, which results in a stretching of the joint capsule. The early stage is called green osselets, and is characterized by a hot, soft swelling at the fetlock. If inflammation damages the cartilage of the joint, the swelling may become chronic and permanent. The joint capsule may also thicken.

Eventually, the bones of the joint will become involved, causing arthritis, pain, stiffness, and periostitis (new bone growth). The fibers of the joint capsule will also increase in size. The long pastern bone may also eventually chip at its front edge, which will leave bone fragments in the joint.

Conformation that encourages osselets to occur include short, upright pasterns, because this conformation promotes concussion.