Total Ankle Replacement Implants Evolving

Total ankle replacements (TAR), have been available in the U.S. for more than 30 years, and are continuing to advance through design evolutions. An article in the September 2008 issue of the Journal of the American Academy of Orthopaedic Surgeons reviews the diverse types of total ankle replacement implants available worldwide, and explains how design improvements are helping to bring relief to arthritis sufferers.

“When we started off, the ankles we used in this country included just two components and we had to use bone cement to fix them and basically they all failed,” said Andrea Cracchiolo, MD, lead author. “The difference between the first generation implants and those today is that you dont need to use bone cement. The surfaces are such that the bone will grow into the joint much like in total hip replacement.”

Available Designs

As it stands now, 4 two-component designs are approved by the Food and Drug Administration for use in the United States (Agility, INBONE, Salto-Talaris, and Eclipse); they are considered fixed implants. In some countries outside of the United States, surgeons have been using three-component ankles for several years.

Three-component ankles could allow for more movement in the joint and may also be easier for orthopaedic surgeons to implant. In the U.S. a three-component device (the Scandinavian Total Ankle Replacement) has been recommended for approval by the Food and Drug Administration. However, it could be late 2008 or longer before it will be made available to U.S. patients.

Biological Ankle Replacement

Another option for total ankle replacement that offers replacement without permanent metal implants. Pioneered by Dr. Daniel K. Lee, director of foot and ankle surgery at UC San Diego Medical Center, this technique is the first in the U.S to offer non-metal, biological ankle replacements to arthritis sufferers.

“Now there is an option that actually restores the ankle with an FDA-approved biologic material that is similar to the collagen found in cartilage,” says Lee. “Unlike a metal device, the advantage to this material is that the implant can be customized in size and contour for every patients individual need,” said Lee. “No matter how the patients ankle is shaped, the collagen is a perfect fit.”

During a two hour minimally-invasive surgical procedure, the damaged cartilage around the ankle joint is removed through a four centimeter incision. The collagen material is then molded into the joint where it adapts to the contour of the patients ankle.

No Risk of Rejection

This material, sourced from either human or animal collagen, has been used for over ten years in plastic and abdominal surgery and heart valve replacement. It is non-allergenic and sterile, so there is no risk of rejection or need for the patient to take immunosupressors.

To permit the material to incorporate fully with the ankle joint, a temporary external device is used to stabilize the joint area while keeping it “distracted” or open for a period of 4-6 weeks.

Attached by small pins, the cylinder-shaped device serves as a shock system to keep the joint free from friction and movement until healing is complete. The device is then removed entirely, which keeps the patients ankle free from any metal parts.

“Within 3 weeks after surgery, we see an incorporation of tissue onto the damaged cartilage,” said Lee. “The idea here is to avoid fusion of the ankle and to add longevity to the joint. We want to give patients as much mobility as possible so they can get back to the activities they love the most.”

Candidates for Ankle Replacements

Total ankle replacements offer more mobility and movement to patients than using fusion to repair the joint, but not all patients are perfect candidates. “Some patients have such deformity of the ankle or have an ankle that is so unstable that total ankle replacement is not indicated,” says Cracchiolo.

Good candidates for a total ankle replacement would have a destroyed ankle, meaning the surfaces of the ankle are gone, have advanced arthritis of the ankle, and the condition of their ankle interfering with daily activities and causing pain.

Advantages of total ankle replacements for patients include better motion of the ankle compared to fusion, protection in the small joints below and in front of the ankle from developing arthritis, and relief of ankle pain.

Concerning the limited number of clinical studies involving such, Dr. Cracchiolo says: “Great care must go in to selecting not only the ideal patient, but also the implant that should be used. We need more long-term follow up clinical studies on implants here in the U.S. In addition, if patients are young, they should understand that the ankle replacement, just like the hip and knee, is not going to last a life time.”

“As improvements in design continue to evolve, the goal is to develop total ankle replacements that are comparable to hips and knees in terms of quality and longevity,”


References:

Design Features of Current Total Ankle Replacements: Implants and Instrumentation: Andrea Cracchiolo, III, MD and James K. DeOrio, MD- J Am Acad Orthop Surg, Vol 16, No 9, September 2008, 530-540.

University of California, San Diego Health Sciences (2008, June 30). Total Ankle Replacement With No Metal. ScienceDaily. Retrieved September 6, 2008, from http://www.sciencedaily.com /releases/2008/06/080624150654.htm

Image by DanDawson, Creative Commons License.