Tarsal Hyperextension
A dog’s tarsus or tarsal joint is the equivalent of the human ankle joint. It is held together by four main ligaments that when damaged can lead to instability of the joint that may require surgery or stabilization through brace use. Generally, your veterinarian can diagnose tarsal instability through physical examination by ranging the joint and observing for any excessive or unwanted movement—further diagnostics may include various imaging techniques such as x-rays or an ultrasound.
Depending on the severity and type of injury surgical correction may include ligamentous repair or fusion of the joint to provide stability. Fusion requires the surgical implantation of a locking steel plate across the tarsus which prevents any movement of the joint1.
Custom articulated braces such as the one shown in the picture below allow for stabilization of the joint while still allowing your dog to maintain full range of motion while preventing unwanted movement such as hyperextension.
Figure 1. Unbraced tarsal hyperextension. Note the backwards angle of the ankle joint.
Figure 2. Custom brace limits the amount of extension allowed at the ankle.