Designed by Frank Alvine, MD, in 1984, the Agility LP Total Ankle Replacement is a two-component prosthesis, which was the first FDA-approved ankle replacement device in the U.S. The Agility device requires an arthrodesis of the distal tibiofibular syndesmosis to increase stability. It also requires the use of an external fixator in surgery to allow proper distraction. One would insert the tibial component in an externally rotated position of 22 degrees to mimic the natural transmalleolar axis. The Agility ankle is approved only with the use of bone cement. Long-term follow up from the creators of the implant have shown between a 90 to 93 percent satisfactory result.12,14
The INBONE total ankle system was approved by the FDA in 2005. The system has a unique design, which is similar to that of a total knee replacement. One would implant the modular, multipiece tibial stem through an intramedullary reaming system. The talar component, also supported by a stem, has a surface of 1.5 to two times larger than other FDA-approved ankle devices.11
Approved by the FDA in November of 2006, the Salto Talaris ankle device is a fixed-bearing ankle prosthesis. The U.S. implant is based off the original Salto prosthesis, a mobile-bearing three component system widely used in Europe. The improved two-component ankle system used in the U.S. utilizes a conical talar component with two different radii of curvature and a curved groove in the sagittal plane. The medial radius is smaller than the lateral to allow equal tensioning of the collateral ligaments. The tibial component is designed for a fixed insertion of the polyethylene bearing piece that is replaceable. The tibial component has a tapered plug on a pedestal, which one inserts through an anterior tibial cortical slot and drill hole in the bone.11
The Eclipse total ankle garnered approval in November 2006. The surgeon inserts the implant through a medial or lateral approach rather than the typical anterior incision required by most TARs. Although this device is FDA-approved, only a few Eclipse total ankles have been implanted and this implant is not readily available to all surgeons.11
Hakon Kofoed, MD, originally designed the STAR implant in 1978 as a two-component, cemented and unconstrained implant. This design was later modified in the 1980s to a cementless, mobile-bearing design. Arguably one of the most widely used ankle implants worldwide, the STAR just received FDA approval for use in the U.S. in May 2009. The STAR ankle is the only U.S. FDA-approved cementless and mobile-bearing, three-component system.
The tibial component is designed for less bone resection and has two parallel bars for insertion into the subchondral bone. The talar component is meant to mimic the talar dome but has a central ridge for stabilization of the polyethylene piece. Both the tibial and talar components are sprayed with titanium plasma to aid in bony ingrowth.15 The first long-term study in the U.S. for the STAR, published in May 2011, reported an implant survival rate of 96 percent at five years and 90 percent at 10 years, which is in direct accordance with previous long-term research in Europe.13