Dependence of implant-bone micromotion on total ankle replacement design features, amount of interference press-fit, and local bone density

Ankle Osteoarthritis (OA) is a debilitating disease that in end-stage has impairment comparable to that of end-stage kidney disease or congestive heart failure. A common treatment option for end-stage ankle OA is total ankle replacement (TAR). TAR has relatively poor survivorship compared to hip and knee replacement. TAR failure is linked to initial implant stability, but little is known about the complex mechanics at the implant-bone interface. The work detailed in this thesis improves upon existing knowledge of TAR implant-bone interfacial mechanics and how implant fixation (line-to-line or interference fixation), implant design, and patient bone density influence early stability, which is indicative of long-term survivorship.

Finite Element Analysis models were developed to analyze the behavior of the tibial components of TAR implants through the stance phase of the gait cycle. Implant performance was quantified by calculating the micromotion between the implant and the bone at discrete steps in simulated gait. Micromotion results show how interference-fit fixation improves implant stability, how different implant designs uniquely resist multiaxial loading, and how implant behavior is highly dependent upon patient-specific bone density.

Implant stability may be achieved through the proper implantation (interference fixation) of an appropriate implant design, chosen specifically for a patient’s bone density. A better understanding of bone-implant mechanics may help us prescribe the most effective treatment option for patients undergoing TAR, leading to improved implant survivorship.