Ankle Arthroplasty

(Ankle Replacement)

Edited by Sam Dellenbaugh, MD

Indication

Ankle replacement is performed as a treatment for end-stage ankle arthritis (See Figure 1). It is typically indicated in older, lower demand individuals, as the lifespan of the ankle replacement is uncertain. Patients that have arthritis (or fusions) involving the joints below the ankle (subtalar, talonavicular and calcaneocuboid joints), may benefit from an ankle replacement, as it will help to preserve some hindfoot motion. Relatively young, active patients typically do not do well with ankle replacements in the long run due to an unacceptably high failure rate. These younger patients are usually best served with a well performed ankle fusion. The results of ankle replacement, unfortunately, have not matched the results we see in knee and hip replacements.

Figure 1A: Normal Ankle Joint on X-ray

Figure 1B: Ankle Arthritis on X-ray (Loss of ankle joint space)

Procedure

The procedure depends on the type of prosthesis that is used. In all ankle replacements, the arthritic surface of the distal tibia is removed, as is the arthritic surface of the top surface talus. Typically only the tibial surface and some of the talar dome are removed (Figure 2). The resected areas of bone are then replaced with the prosthesis.  The prosthesis typically has a metal surface on the tibia, and talar sides with a polyethylene surface attached to the tibial component.

Figure 2: Tornier Salos Talaris Total Ankle Replacement

Potential Complications

These include the potential complications that can occur with any surgery such as:
There are some specific complications that occur with total ankle replacement including:
Deep Infection of the Prosthesis
The deep wound infection rate in patients undergoing Total Ankle Replacement is not necessarily any higher than with other major ankle surgery, however, the significance of a deep infection is profound. A deep infection often requires removal of the prosthesis in order to eradicate the infection. The deep infection rate is approximately 1-3%.

Major Wound Breakdown. 
Most total ankle replacements are inserted through an incision in the front of the ankle. This area of tissue has a somewhat tenuous blood supply. It is supplied by one main artery, whereas most other areas of the body are supplied by two or more major arteries. For this reason, some difficulty with wound healing occurs at a much higher rate in patients undergoing total ankle replacement. Often, this requires immobilizing the ankle for a few weeks to improve the chances of successful wound healing.  In some patients, however, an area of wound breakdown or a failure to heal the surgical incision occurs. This can be a difficult and potentially devastating complication because the failure to obtain adequate wound healing can lead to a deep infection involving the prosthesis.

Tibial Nerve Injury
There is a chance of an injury to the surrounding nerves, including the tibial nerve, when the ankle joint is prepared to receive the ankle prosthesis.

Failure of the Ankle Replacement over time
All joint replacements will eventually fail if the patient uses the joint enough, and lives long enough. There are a variety of ways that joint replacements can fail, each of which lead to pain and dysfunction. Perhaps the most common mode of failure of a joint replacement is from shifting of the prosthesis, when the supporting bone becomes weak from repetitive loading or osteolysis, breakdown of the bone under the prosthesis resulting from a reaction of the immune system to very small particles of the polyethylene section of the prosthesis.

Total ankle replacements historically have failed earlier, and at a substantially higher rate, when compared to knee and hip replacements. For example, studies have suggested that certain hip replacements have good or excellent results in over 90% of patients after 18 years. In knee replacements, the figures are close to 90% success after an average of 13 years. However, in ankle replacements, the best prospective study suggests that 85% of patients have a successful result after 5 years - not bad, but no where near as successful as knee and hip replacement surgery.

Ankle replacements fail at a higher rate because of a variety of factors related to the ankle joint itself. These include:
  • the small joint surface area (half the size of the knee joint)
  • high joint reactive forces during walking (2-4 x body weight, almost twice that of the knee joint)
  • Uneven distribution of force across the tibial prosthesis
  • The lower bone of the ankle (Talus) is relatively small and has a poor blood supply, providing a less than ideal base of support for the prosthesis.
  • There are limits to how much bone can be removed from the ankle joint, and this limits the size of polyethylene that can be used. The smaller the polyethylene, the poorer the wear characteristics
  • The relatively confined nature (many important structures nearby) of the ankle joint makes placing an ankle replacement technically challenging for the surgeon.

When an ankle joint fails, a revision surgery is necessary. Often the prosthesis can be replaced. However, there is much less bone stock available around the ankle, so revision surgery is often substantially more difficult with results that are less predictable than the original operation. If the prosthesis cannot be replaced, the ankle joint is then fused, but studies show that patients who have an ankle fusion after a failed ankle replacement do poorer than patient who have an ankle fusion first.

Edited May 9, 2017

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