CONDITION
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.
Why this matters now
Tarsal hyperextension injury can occur at any age, though it tends to be seen more often in young, active dogs and in working or sporting breeds that regularly jump, turn sharply, or navigate uneven ground. Cats may sustain this injury after falls from height or during outdoor mishaps. In some animals the injury follows a single clear event—a stumble, a leap, a collision—while in others the damage accumulates gradually, particularly in individuals with generalised joint laxity or those recovering from other hind-limb problems that alter weight distribution.
The change in hock posture may appear suddenly, particularly if the injury involves a complete rupture of one or more supporting structures, or it may develop over days to weeks if the damage is partial or if compensatory strain builds over time. Some animals show a stable pattern early on, with little further deterioration, while others experience progressive collapse of the joint as remaining intact structures stretch under the altered load. The degree of lameness and the extent to which the hock drops during weight-bearing often reflect both the severity of the initial damage and the body's response in the days and weeks that follow.
Signals & patterns
Early signals
Hock sitting lower on one side
When the dog or cat stands or walks, one hock may appear closer to the ground than the other, giving the limb a slightly flattened or sunken appearance. This change in posture is often most visible when weight shifts fully onto the affected leg.
Altered gait on the hind leg
The animal may take shorter steps on the affected side, or the leg may move with a slightly awkward, rolling motion as the hock fails to hold its usual angle. Owners sometimes describe the movement as looking effortful or uneven, though the limb may still bear weight.
Reluctance to jump or climb
Activities that require forceful push-off from the hind legs—leaping onto furniture, navigating stairs, or jumping into a car—may become noticeably less fluid or may be avoided altogether. The animal may hesitate or adjust its approach in ways that reduce load on the affected hock.
Swelling around the hock joint
The area around the hock may appear slightly thickened or puffy, particularly in the first hours or days after injury. This swelling reflects fluid accumulation and early inflammation in and around the damaged structures.
Subtle shift in standing posture
When at rest, the animal may favour the opposite hind leg or distribute weight unevenly, sometimes shifting the affected limb slightly forward or to the side. These small adjustments often indicate discomfort or instability at the hock.
Later signals
Hock touching or nearly touching the ground
In more advanced cases, the joint may collapse almost entirely under load, with the back of the hock making contact with the ground during standing or walking. This complete loss of normal joint posture typically indicates severe damage to multiple supporting structures.
Persistent lameness or stiffness
The limp may become more consistent and pronounced over time, particularly if the injury does not stabilise or if secondary changes develop in the joint. Stiffness after rest is common, and the gait may worsen with prolonged activity.
Muscle wasting in the affected leg
Over weeks to months, the muscles of the thigh and lower leg on the injured side may become visibly smaller than those on the opposite limb, reflecting reduced use and altered load-bearing. This atrophy tends to develop gradually and may be subtle at first.
Thickening or firm feel around the joint
Chronic inflammation and the body's attempts at repair can lead to persistent swelling and a firmer, less mobile feel to the tissues around the hock. This may be accompanied by reduced range of motion when the joint is gently moved.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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