Design features of current total ankle replacements: implants and instrumentation.

Development of total ankle replacements began nearly 40 years ago. The initial devices were cemented and highly constrained, and they eventually failed. These were followed by second-generation cementless ankle implants with a fixed (two-component design) or mobile (three-component design) polyethylene bearing. Currently, four ankle replacements are approved by the US Food and Drug Administration. These four-Agility, INBONE, Salto-Talaris, and Eclipse-are two-component designs; the Scandinavian Total Ankle Replacement, a three-part mobile-bearing design, has been recommended for approval by the FDA. It is anticipated to arrive in the US market in late 2008. Although interest in total ankle replacements is increasing, midterm clinical results to date are few and often have not been validated by independent practitioners. In addition, no level I or II studies have been published. Therefore, the design rationale for these implants and instruments should be carefully evaluated.