Tarsal (hock) hyperextension, also known as luxating or popping hocks, is a condition where the hock is able to move cranially (forward), past the line of perpendicular to the ground. When you see this in a dog, it appears as though the hock is moving in the wrong direction, “popping forward” – it is actually hyperextending. While this can occur secondary to a traumatic injury, most commonly this is associated with a rear limb conformation that is very straight, with minimal to no bend of stifle (knee). It can also be associated with dogs that have problems in the hips or stifles, as they learn to compensate for these by moving the lower leg in positions to alleviate the pain associated with the upper joint condition. Over time, the ligaments become stretched in the wrong direction due to the way the dog is load bearing, which then allows the hock to hyperextend.
There are various degrees of tarsal hyperextension. It can be minor, only seeing it occasionally when the dog is standing still and the hock “pops” forward for a moment, yet while moving the dog appears sound. Other times, it can be severe enough that the dog can simply not keep its hind leg stable and while standing or moving, the hock will hyperextend forward significantly. Either way, it is an instability in this joint and will, most likely, cause the development of osteoarthritis in the joint over time.
The only veterinary treatment that can be done for these dogs is to surgically fuse the hock joint. This will create a more stable joint for the dog to support himself with. However, this is not commonly done and would require an orthopedic specialist for the surgery. Many people elect to use orthopedic braces for these dogs, depending on the severity of the condition. If the hock is only luxating mildly, often times regimented physical therapy may be an option to keep the ligaments in the joint as strong as possible for stabilization.
There is no genetic marker available for this condition at this time. Breeders should be cognizant of the rear limb conformation in the dogs they use in their breeding programs and be aware of how this condition relates to conformation.
