Anatomy of the tarsus

Diseases of the tarsus are a common cause of hind-limb lameness in horses.

The equine tarsus (hock) consists of five joints and six bones aligned in three rows. The central tarsal bone is located in the second row. The distal tarsal bones have two main functions: they absorb shock and neutralize twisting forces. The tarsal bones undergo axial compression, tension and some torsional loading during exercise. Because of its anatomic arrangement, the central tarsal bone absorbs most of the forces transmitted through the cuboidal bones. The proximal intertarsal, centrodistal and tarsometatarsal articulations are plane joints and are only capable of minimal amounts of gliding movement.

The tarsus is heavily invested by collateral and periarticular ligaments, so fractures and luxations of this region are not particularly common.
With fractures caused by external impact, often the exposed portions of the tarsus are fractured, like the sustentaculum tali or the trochlear ridges. Moreover rotatory twisting accidents can cause fractures. Most of the fractures are closed with the exception of the calcaneus and the sustentaculum tali.