The ankle joint is a comparatively small joint relative to the weight bearing and torque it must withstand. These factors have made the design of total ankle joint replacements technically challenging. Total ankle replacements have been investigated since the 1970s, with initially promising results, but the procedure was essentially abandoned in the 1980s due to a high long-term failure rate, both in terms of pain control and improved function. Newer models have since been developed, which can be broadly subdivided into two design types, fixed bearing and mobile bearing.
1) Fixed-bearing designs lock the polyethylene component into the baseplate, which provides greater stability, but increases constraint and edge-loading stress at the bone implant interface, potentially increasing risk of early loosening and failure. The fixed-bearing devices are implanted with cement fixation (e.g., the Agility Ankle Revision; the Topez Total Ankle Replacement; the Eclipse Total Ankle Implant; the Inbone™ Total Ankle System; the Salto Talaris Total Ankle Prosthesis).
2) Mobile-bearing systems have a polyethelene component that is unattached and articulates independently with both the tibial and talar components. The 3-piece mobile-bearing prostheses are designed to reduce constraint and edge loading, but are less stable than fixed-bearing designs and have the potential for dislocation and increased wear of the polyethylene component. Mobile-bearing designs are intended for uncemented implantation (e.g., Scandinavian Total Ankle Replacement (S.T.A.R. Ankle)) and have a porous coating on the components to encourage osseo-integration. The Buechel-Pappas device and the TNK ankle are additional mobile bearing devices, however they not approved for use by the FDA.
3) Encouraged by the excellent results attained by total joint arthroplasty of the hip and knee, several surgeon-engineer teams designed and developed total joint prostheses for the ankle. In the early and middle 1970`s reports appeared of early success with these implants in 80% to 85% of patients. In 11 reports that included 346 arthroplasties, good or fair results were reported in 83% and failures in 17% at a mean follow-up of less than 5 years. A wave of enthusiasm developed for total ankle arthroplasty, and the indications for the procedure were expanded, often to include young people engaged in strenuous work or recreational activities. After further experience and longer periods of observation, reviews of most series of total ankle arthroplasties revealed extremely poor long-term results, especially in younger patients with isolated traumatic arthritis. In later reports in which the average follow-up was longer than 5 years, failure occurred in 35% to 76% of arthroplasties.
4) Comparison of long-term series of total ankle arthroplasty are difficult because of variability in diagnosis, patient age, length of follow-up, prosthesis design, and absence of a uniform scoring system. The largest series of total ankle arthroplasties is that of Kitaoka et al. (1994, 1996), who reported their experience with 204 primary Mayo total ankle replacements. The overall cumulative rate of implant survival was 79% at 5 years, 65% at 10 years, and 61% at 15 years. The probability of an implant being in place at 10 years was 42% for patients 57 years of age or younger and who had previous operative treatment of the ipsilateral ankle or foot and 73% for those older than 57 years of age who had no such previous operative treatment. Because of these poor long-term results, they do not recommend the use of the Mayo total ankle arthroplasty, especially in younger patients who have had a previous operative procedure on the ipsilateral ankle or foot. In a series of 36 constrained Conaxial (Beck-Steffee) ankle replacements, Wynn and Wilde (1992) found that 27% were loose at 2 years, 60% at 5 years, and 90% at 10 years; they recommend that this ankle prosthesis not be implanted.
5) Complications other than implant loosening also are more frequent after total ankle arthroplasty than after total hip or knee replacement. Delayed wound healing has been reported to occur in as many as 40% of patients, and most long-term series cite rates of deep infection of 3% to 5%. Loosening has been reported in 6% to 25% of implants after 3 to 5 years; usually the talar component is involved. Demottaz, et al. (1979) reported radiolucent zones of 2 mm or more at the cement-bone interface in 88% of prostheses at 1 year, and Unger et al. (1988) reported talar subsidence in 14 of 15 arthroplasties and tibial component tilting in 12 of 15 at an average 6-year follow-up. Wynn and Wilde (1992) reported an overall complication rate of 60%, including wound dehiscence (39%), deep wound infection (6%), fractures of the medial or lateral malleolus (22%), and painful talofibular impingement (14%).
6) Although some more recent reports of uncemented, unconstrained replacements have shown better short-term results, currently no ankle implants are available that provide consistently good long-term results. There are no prospective randomized controlled clinical trials comparing total ankle replacement to fusion or other alternatives. In a review of total ankle arthroplasty, Saltzman (1999) concluded that despite efforts to develop a workable total ankle replacement the long-term results of most new designs are unknown. Saltzman concluded that prospective clinical trials are needed to determine which factors lead to successful and unsuccessful outcomes.
7) In a review on total ankle replacement, Hintermann and Valderrabano (2003) stated that although the results of the different design approaches are encouraging in limited clinical series, there is still the need for careful, long-term analyses to estimate to what extent the current designs are mimicking the biomechanics of the ankle joint. More attention must be paid to more accurate implantation techniques that result in a well-balanced ligament and allow the ligaments to act together with the replaced surfaces in a most physiological manner. Gill (2004) noted that there is a need for further basic science research in total ankle arthroplasty. The lessons learned from other arthroplasty should be considered in ankle arthroplasty design.
8) Van den Heuvel and colleagues (2010) stated that the ankle joint has unique anatomical, biomechanical and cartilaginous structural characteristics that allow the joint to withstand the very high mechanical stresses and strains over years. Any minor changes to any of these features predispose the joint to osteoarthritis. Total ankle replacement is evolving as an alternative to ankle arthrodesis for the treatment of end-stage ankle osteoarthritis. Initial implant designs from the early 1970s had unacceptably high failure and complication rates. As a result many orthopedic surgeons have restricted the use of TAR in favor of ankle arthrodesis. Long-term follow-up studies following ankle arthrodesis show risks of developing adjacent joint osteoarthritis. Thus, research towards a successful ankle replacement continues. Newer designs and longer-term outcome studies have renewed the interest in ankle joint replacement.