Femoral implants comparison by means of thermoelastic stress analysis

Abstract

The structural analysis of bone implant stresses has been here performed experimentally, by means of thermoelastic stress analysis, that is a quite recent full field technique, rarely exploited in orthopaedic biomechanics. Five synthetic femurs have been employed: one was left unimplanted, two were implanted with model A prosthesis and two were implanted with model B prosthesis; each femur has been tested with various spherical heads which realised different head offset with respect to the diaphyseal axis. The femurs have been loaded with an apposite testing rig, able to operate indynamic conditions, with high test repeatability. Three main parameters have been identified: the prosthesis model, the implant position, the moment arm of simulated articular force; the respective thermoelastic stress maps have been analyzed following three main procedures. First, peak stress values and their location have been identified; secondly the statistical distribution of stresses has been examined looking at its average value, its variance and its shape. Finally, the pattern of stresses towards the respective vertical quote has been analyzed. All these procedures considered the unimplanted femur as a reference. Results have pointed out the ability of this experimental analysis to analyze out how stress pattern changes in relation to different implant models, position and different femoral offset, allowing to identify which configuration is closest to the physiologic condition. The indications provided can be a useful aid to choose among different implant configurations, with the final aim of a longer implant duration and, consequently, a higher quality of life. (Among four finalists for Clinical Biomechanics Award, Invited Presentation at Plenary Session)