What is tarsal arthrodesis?

Tarsal arthrodesis is surgical fusion of the tarsus (hock joint), which is analogous to the human ankle joint. This is a complex joint comprised of seven short, broad bones arranged in several levels with low-motion joints in between. The two tarsal bones at the top of this joint are called the talus and the calcaneus. The talus bone contacts the end of the tibia at the high-motion talocrural joint, which is responsible for flexion and extension of the hock. The calcaneus lies next to the talus, and has a long projection that forms the heel, which serves at the attachment point for the Achilles tendon. The tarsal bones are held together by a network of ligaments and tendons. 

The tarsal arthrodesis is used to address cases of advanced tarsal joint arthritis or tarsal joint instability that cause discomfort and prevent normal limb use. Tarsal arthritis may develop due to an old osteochondrosis lesion, chronic joint laxity, joint infection, or immune-mediated inflammation. These conditions are diagnosed with a physical exam and x-rays. In most cases, instability is a result of traumatic injury to the ligaments and/or tendons supporting the joint. Tarsal joint instability is diagnosed with sedated palpation and stressed-view x-rays, in which pressure is applied to the joint from different directions to reveal abnormal laxity where tissues have been torn. In some cases of instability, surgery can be performed to repair or replace the damaged structure, but in many cases, joint fusion is the best option.

There are two types of tarsal arthrodesis surgery: partial tarsal arthrodesis and pan-tarsal arthrodesis. In a partial tarsal arthrodesis, only the low-motion joints between the tarsal bones are fused; this preserves most of the hock’s function, but is only possible when the instability does not involve the talocrural joint. If the talocrural joint is involved, then a pan-tarsal arthrodesis will be needed. In a pan-tarsal arthrodesis, all of the joints in the tarsus are fused; this prevents all motion of the hock joint. In both types of surgery, the joint is opened and all of the joint cartilage is removed. The former joint spaces are packed with a cancellous (spongy) bone graft harvested from the upper humerus or pelvis. Finally, a specially-designed arthrodesis plate is firmly secured with surgical screws across the fused joint(s) to prevent motion while the former joint spaces fill in with bone. If a partial tarsal arthrodesis is performed, the plate will most likely be located on the side of the joint, while pan-carpal arthrosis plates are typically located on the front of the joint. 

What patients can benefit from a tarsal arthrodesis?

Any patient with advanced arthritis of the hock or hock joint instability (usually from trauma) that causes discomfort and/or impairs mobility may benefit from a tarsal arthrodesis. A physical exam and x-rays will enable your veterinarian to determine if this procedure is right for your pet. 

What post-operative care is required?

Following tarsal arthrodesis, patients go home with a splint on the limb to provide additional support. This splint will remain in place for the first four to six weeks after surgery, and will be re-bandaged in the clinic weekly to monitor the healing of the incision and treat any irritation or bandage sores that may develop. During these first four to six weeks, physical activity must be kept to a minimum, with only short, slow leash walks to use the bathroom. At all other times, it is recommended that patients remain in a kennel or small room where they cannot run, jump, or play with other pets. A set of post-operative x-rays is taken about six weeks after surgery, and if bone formation is progressing as expected, splint use may be discontinued at this time. It is still essential at this point to avoid all high-impact activities, such as running, jumping, or playing with other pets, but longer controlled walks will be permitted. X-rays will be repeated every four to six weeks until complete bone fusion is present, at which point the patient can return to full activity. For most patients, this point is reached three to four months after surgery.

What are the potential risks and complications of a tarsal arthrodesis?

Potential complications following a tarsal arthrodesis include bandage irritation or sores, infection, implant breakage, loosening, or bending, failure of the joint to fuse within the expected time frame, and sensitivity adjacent to the plate in cold weather. 

The risk of developing irritation or sores under the bandage is minimized by the careful application of bandage padding, close attention to keeping the bandage clean and dry at home, and weekly bandage replacement to enable the early detection and treatment of any problems that arise. 

The risk of infection is minimized by the use of sterile surgical technique and meticulous bandage application and maintenance. A superficial infection of the skin incision is treated with a standard course of antibiotics, while an infection that extends all the way into the bone requires an extended course of antibiotics, and often necessitates the removal of the surgical implants once the arthrodesis has completely filled in with bone. 

Implant breaking, loosening, or bending may either be the result of the use of an insufficiently-sized implant or of overuse of the limb before bony fusion has completed. Any implant, no matter how large, will fail if repeatedly subjected to the forces exerted by an active dog. Damage to the implants will necessitate a second surgery to remove and replace them. 

Failure of bone fusion within three to four months may be the result of insufficient stabilization, impairment of the blood supply to the area, poor health, or advanced age. Depending on the underlying cause, a second surgery may be performed to replace the implants with stronger ones and/or add more bone graft to the former joint spaces. A cast or splint will likely be applied for another four to six weeks after this intervention. 

Some degree of cold-weather associated sensitivity around the area of the plate is commonly experienced by patients who have had a tarsal arthrodesis because the plate is located just beneath the skin, where it readily conducts cold into the underlying tissues. If this causes significant discomfort, the implants can be removed with a second surgery as long as bone fusion is complete.

What is the prognosis with this surgery?

The prognosis with a partial tarsal arthrodesis is very good, with most patients achieving pain-free normal to near-normal limb use within three to four months following surgery. Pantarsal arthrodesis is also very effective for pain relief, but because the high-motion part of the hock joint is fused into a neutral (standing) positon, the patient’s gait will always be somewhat abnormal. They may initially seems awkward in their movements as they get used to this change, but most patients adapt quickly and are able to engage in all of their favorite activities. 

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