An Achilles tendon rupture is also known as a rupture of the gastrocnemius tendon, or the common calcanean tendon. The tendon is actually composed of 5 different tendons, the two most important being the superficial digital flexor and gastrocnemius tendons. The gastrocnemius tendon is the largest of these, and is the most powerful extensor of the hock (ankle) joint. Both the superficial digital flexor and gastrocnemius tendons attach to the heel bone, called the calcaneus bone. A rupture of the Achilles tendon may be a partial tear, which means just the gastrocnemius is torn, or a complete tear, in which all five tendons have been torn. (show diagrams, normal anatomy vs partial vs complete tears)
Dogs that are affected by an Achilles tendon rupture are primarily from the large sporting and working breeds, and are usually 5 years of age and older. The Doberman pinscher and Labrador retrievers seem to be overrepresented in this condition, but it can occur in any dog or cat, no matter what age or breed.
With a partial rupture, the gastrocnemius tendon is torn, but the superficial digital flexor tendon is still intact. Animals with a partial rupture will have a dropped hock, be lame in the affected leg, and will stand with curled toes. Dogs that have a complete rupture and all five tendons of the Achilles tendon are torn will have a completely dropped hock, so that he is walking flat-footed rather than on his “tippy toes” like normal, and will show signs of lameness. (show pictures of affected animals with dropped hock) Pain and edema (swelling) will follow the injury. Eventually the gastrocnemius muscle will contract, and the area between the bone and the tendon fills with fibrous tissue.
Rupture of the Achilles tendon can usually be diagnosed based on clinical signs and physical exam. Radiographs may also be used, and ultrasounds can be useful in distinguishing between partial and complete tears.
Achilles tendon rupture can be caused by a sudden traumatic event such as a fall, or anything that causes a sudden and extreme flexion of the hock. Rupture may occur over time due to extreme overstretching and overuse which can cause the tendon to deteriorate and eventually tear. Lacerations are the most likely cause of a complete tear.
Because the muscle contracts when the tendon is ruptured, it results in permanent deformity, so medical management using a cast or splint will not work and the injury must be repaired surgically. The surgical procedure involves removing the damaged portions of the tendon so that the ruptured ends can be reattached together. To reattach the gastrocnemius tendon to the heel bone, bone tunnels are drilled and special nonabsorable sutures are passed through the tunnels and into the gastrocnemius tendon. If the SDF tendon is also ruptured, the ruptured portions are stitched back to one another using heavy suture material in a special suture pattern (locking loop) that pulls the torn tendon ends back together. After the tendon(s) have been repaired, the patient must keep the ankle (hock) in extension for a period of two months, so that the surgery does not fail. After two months the method of stabilization of the hock is removed. Methods to do this include: placement of a screw through the tibia and heal bone with the hock in extension and a cast is usually also applied to the limb; placement of an external skeletal fixator which consists of a series of pins that penetrate the bone and are fixed together with external bars; placement of a circular fixator ring with wires; placement of a cast.
Prognosis with surgery is generally very good. The sooner and Achilles tendon rupture is repaired, the better the results will be. If the tear goes without repair for too long, the formation of scar tissue will make the surgery more difficult and possibly less successful. Additionally, if the animal walks plantigrade (like a human with toes and ankle on the ground) for an extended period of time further damage can result which will make surgery more difficult. It is also important to note that there is significant aftercare in this surgery due to the placement of a cast, possible external fixators or screws, and strict exercise restrictions and rest. Total recovery takes from 8-10 weeks. The final outcome of the surgery also depends on the aftercare of the patient.