MECHANICAL VALIDATION OF WHOLE BONE COMPOSITE FEMUR MODELS

Composite synthetic models of the human femur have recently become com mercially available as substitutes for cadaveric specimens. Their quic k diffusion was justified by the advantages they offer as a substitute for real femurs. The present investigation concentrated on an extensi ve experimental validation of the mechanical behaviour of the whole bo ne composite model, compared to human fresh-frozen and dried-rehydrate d specimens for different loading conditions. First, the viscoelastic behaviour of the models was investigated under simulated single leg st ance loading, showing that the little time dependent phenomena observe d tend to extinguish within a few minutes of the load application. The behaviour under axial loading was then studied by comparing the verti cal displacement of the head as well as the axial strains, by applicat ion of a parametric descriptive model of the strain distribution. Fina lly, a four point bending test and a torsional test were performed to characterize the whole bone stiffness of the femur. In all these tests , the composite femurs were shown to fall well within the range for ca daveric specimens, with no significant differences being detected betw een the synthetic femurs and the two groups of cadaveric femurs. Moreo ver, the interfemur variability for the composite femurs was 20-200 ti mes lower than that for the cadaveric specimens, thus allowing smaller differences to be characterized as significant using the same simple size, if the composite femurs are employed.