Tarsal Hyperextension Injury

Tarsal hyperextension injury describes a situation in which the hock—the angular joint roughly midway down the hind leg—drops lower than usual when weight is placed on the limb, sometimes touching or nearly touching the ground. This happens when the structures that normally hold the joint in its natural position (ligaments, tendons, the joint capsule itself) are stretched, torn, or otherwise compromised. The change in posture is often visible when the dog or cat walks or stands, and the limb may appear to sink or flatten at the hock. Owners often notice a sudden or progressive change in the way the hind leg looks when their pet moves—perhaps after a fall, a jump, or sometimes without an obvious incident. The limb may still bear weight, but the hock sits closer to the ground than the opposite side, and the gait may look awkward or effortful. In some cases the change is subtle; in others the joint appears to collapse entirely when standing. This page explores what signals tend to accompany this kind of injury, what is happening to the structures inside and around the hock, how the injury is investigated, and what approaches exist for managing it. The shape and severity of the problem can vary considerably, and the path forward depends on the extent of the damage and the individual animal's circumstances.