+ Tarsal hyerextension injury is due to tearing of the ligaments on the bottom side (plantar) of the paw
+ Treatment involves fusion of the joint
+ Prognosis is generally good with surgical treatment
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The hind paw of the dog is similar to the foot in man. It is made of many small bones that form multiple joints. The top joint (ankle) is very flexible, whereas the remaining joints have limited range of motion. The backside (plantar side) of the tarsus is supported by a very strong ligaments, which prevents the joints from over extending (hyperextension).
Cause of tarsal hyperextension injury
The cause of a hyperextension injury is due to tearing of the plantar ligaments. This type of injury can be due to a single isolated traumatic event. In other cases it is due to repeated injury to the ligaments. Once the plantar ligaments tear, conservative measures such as splinting or casting the limb are ineffective. Some breeds have a genetic condition (like Shetland Sheep dogs), are prone to degeneration of the ligaments that hold the joints together and develop hyperextension of the tarsi and carpi.
Tarsal hyperextension injury is seen large and small breed dogs. Warning signs of this condition include lameness and an abnormal shape of the paw (as seen right). The toes may curl (hyperflex) and the hock may sink down with weight-bearing. In the acute injury, the area may be swollen and painful on palpation.
The diagnosis of a tarsal hyperextension injury is based on physical examination findings and x-rays of the affected forelimb. The surgeon likely will take stress x-rays of the affected limb, with your pet under anesthesia. This involves applying a stress to the tarsus to see which joints have torn ligaments. Take note of the stressed radiograph (far right as compared to the non stressed radiograph).
The day of surgery
The anesthesia and surgical team will prescribe a pain management program, both during and after surgery that will keep your companion comfortable. This will include a combination of general anesthesia, injectable analgesics, local anesthesia (Nocita), oral analgesics and anti-inflammatory medication. The surgeon will call you following surgery with a progress report.
In order to address a tarsal hyperextension injury, it is essential to perform an arthrodesis or fusion of the affected tarsal joint(s). This involves removing the cartilage from the surfaces of the bones within the affected joint(s), packing the joints with a bone graft (typically from the bone bank or collected from the patient) and stabilizing the bones with a plate and screws. The surgeon will have made a determination prior to surgery if a partial arthrodesis (photo right) or a full arthrodesis is necessary. The full arthrodesis will remove all movement within the tarsus, whereas the partial arthrodesis retains range of motion of the ankle.
After surgery, you can continue to give your pet a prescribed pain reliever to minimize discomfort. A splint or cast will be used to support the repair for six to eight weeks. The splint or cast will need to be changed by your dog’s surgeon at least every other week. It’s also extremely important to limit your dog’s activity and exercise level during the post-operative period. The surgeon will monitor the healing process with a series of follow-up exams. At about six to eight weeks after the surgery, x-rays will be made to evaluate the healing of the arthrodesis site. Subsequent x-rays may be required on a monthly basis until the arthrodesis site has completely healed.
Surgical arthrodesis will relieve your companion’s pain once the bones have fused together. Partial arthrodesis commonly will allow your pet to have normal function of the limb with good range of motion of the ankle (hock). A full arthrodesis of the tarsus typically results in good function of the limb; however, a gait abnormality is expected, as the ankle will not have any movement. Uncommon complications following surgery include infection, failure of the bones to fuse together, breakage of the implants (metal plate and screws) and cold sensitivity. In general, about 90 to 95% of the patients will respond well to the surgery.