Mechanical Analysis of Osseointegrated Transfemoral Implant Systems

Abstract

Osseointegrated transfemoral implants have been introduced as an alternative to conventional, socket-based prostheses for above knee amputees. This method is showing great promise; however, the frequency of device failure is of concern. As a means to understand some of these failures, this study investigates the mechanical behaviour of three osseointegrated transfemoral implant systems; an in-house prototype design and two assemblies comprised of implant-grade parts provided by Integrum AB, Sweden. A series of mechanical tests were administered to evaluate the effects of tightening specifications and connection geometry on the material response, and mechanical behaviour of the assemblies. The tests included torque-elongation measurements, torque to failure tests, and strain analyses during loading. This research was carried out in an attempt to better understand the behaviour of components under loading, in order to optimize the assembly specifications and improve the useful life of the system. The results obtained confirm that the Integrum assemblies exhibit improved performance when tightened to a level beyond the current specified tightening torque of 12 Nm. Increased tightening torque provides an improved connection between components, leading to increased torque retention, decreased peak tensile strain values and a more gradual, primarily compressive distribution of strains throughout the assembly.