LOS ANGELES, California—Ankle fusions may go the way of the dinosaurs as total ankle replacement surgeries begin to catch up with hip and knee replacements, according to a review article in the September 2008 Journal of the American Academy of Orthopaedic Surgeons.¹ According to the authors, new ankle prostheses rival hip and knee devices in design, function, and potentially durability. Although the number of ankle prostheses is not likely to approach the demand for new hips and knees, the pipeline is brimming with new prostheses for patients who are good candidates for total ankle replacement.  

“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,” said one of the review authors Andrea Cracchiolo III, MD, director of the adult foot and ankle section at UCLA Medical Center in Los Angeles.

The evolution of total ankle replacements: getting up to speed from a slow start

“We started in the late 1970s and after a few years, it was obvious that ankle implants were failing, so almost everyone stopped doing them,” explained Dr. Cracchiolo. The 2-component first-generation of ankle replacements were nonanatomic and were fixed in place with bone cement. Newer devices do not require bone cement but have surfaces such that the bone will grow into the joint.

Only four devices are currently Food and Drug Administration (FDA)-approved, and all are the older 2-component system. In Europe and other countries, however, orthopaedic surgeons have been using 3-component ankles for several years. These ankles may allow for more movement in the joint and may also be easier to implant. In the US, a 3-component device?the Scandinavian Total Ankle Replacement?has been recommended for approval by the FDA, but it is unlikely to become available before late 2008.

Three-component ankles are “probably the wave of the future,” Dr. Cracchiolo said. “They are a little easier to [implant] and provide more stability.”

Dearth of data impedes acceptance

While the pipeline is full, there is a dearth of clinical trial data on the new ankle implants. “We don’t have any good numbers in terms of success.” The reasons are multifaceted according to Dr. Cracchiolo. For starters, “most good orthopedic surgeons who are doing foot and angle replacements do 50, 60, or 70 a year. If you want a 5-year follow–up, it will take 8 years [to accrue patients]. Most people would like to have their pain relieved and a moveable ankle, but we have to explain that we don’t know what the mid- or long-term results are. Some patients should not have ankle replacement because they have too much deformity or too much instability, and we might want to encourage a fusion instead of replacement at this time. But for patients who don’t want fusion due to restricted motion, it is safe to proceed, [however], we just don’t know the results long-term.”

Unlike hip or knee replacement candidates, “most ankle patients are younger, more active and will live longer, so until we get some other breakthrough such as cadaver transplant, these implants will cover the bases.”

Translating research into practice

“Over the last 10 years, there has been a relatively larger number of total ankle replacements done around world, and in the US and they have shown a large improvement over the first phase,” agreed Charles Saltzman, MD, president-elect of the board of directors of the American Orthopaedic Foot and Ankle Society (AOFAS) and department chair of orthopaedic surgery at the University of Utah in Salt Lake City.

“I think we are moving toward designs that respect the ligamentous anatomy, control motion in a way that is natural and not bulky, that take out the minimal amount of bone, and that have the potential for long-term wear. When we arrive at that point, fusion will not be a good option anymore.”

The evolution of ankle replacements is following that of hip and knee replacements. “Things have really changed since 1960s and 1970s and the total ankle world is following in the same path [as hip and knee arthroplasty], but it is just slower to develop,” Dr. Saltzman added.

An unanticipated factor in the growing demand for ankle replacement devices is the widespread use of automobile airbags. “With the advent of airbags and the use of seatbelts, we are seeing many people survive horrifying accidents who would not have survived, but airbags don’t protect the ankle,” he said. “The prevalence of endstage ankle arthritis has risen and will continue to rise, and the industry now realizes there is a market and are pulling to invest.”

Reference

1. Cracchiolo III A, DeOrio JK. Design features of current total ankle replacements: implants and instrumentation. J Am Orthop Surg. 2008;16:530-540.