Hock
Introduction
The hock is similar to the knee as it consists of more than one joint. There are four joints that make up the hock, the tarsocrural joint, the proximal intertarsal joint, the distal interstarsal joint and the tarsometatarsal joint. The tarsocrural joint, between the tibia and the talus bone, is where most of the flexion occurs. The proximal intertarsal joint is between the calcaneus, which lies behind the talus and forms the point of the hock, and the talus bone and the first row of small hock bones. The distal intertarsal joint is between this row and a second row of hock bones and the tarsometatarsal joint is between this second row and the canon bone. There is little movement of these three lower hock joints in horses. There are also many ligaments within the hock that provide the joint with its support. The superficial flexor tendon runs over the point of the hock and is cushioned by the calacaneal bursa it then passes through the tarsal sheath, a synovial fluid-filled structure that runs down the hock. The hock region is probably the most common site of hindlimb lameness, with degenerative joint disease (arthritis or bone spavin) being the most common. Often lameness associated with the hock is made worse after a flexion test, also known as a spavin test.