Effects of mechanical loading on the profile of human femoral diaphyseal geometry

In vivo bone behaviour predictions with respect to altered loading conditions, implants, and endoprostheses are highly desirable to avoid untoward effects such as implant loosening and breakage. This knowledge does not relate only to the result but also to the mechanisms of bone adaptation and bone growth. Since bone growth is assumed to be determined essentially by the loading history, the morphology of the human femoral midshaft region was analysed to extract those loading cases responsible for the actual cross-sectional geometry. This was achieved by the application of computer-aided optimization (CAO), a procedure supplementing a finite element analysis which allows for simulation of adaptive bone growth. A simulated load was applied to a cylinder, and the resulting changes in geometry were compared with the geometry of three ex vivo samples. Apparently, standard loading cases alone (axial loading, bending, torsion), or at consecutive or simultaneous application, did not yield the characteristic morphology of the femoral shaft region. Only the introduction of the adductor muscle force in various combinations with other standard loadings resulted in femoral mid-shaft geometries comparable with the ex vivo specimens.