Distribution of mechanical robustness in the human femoral shaft

The object of the present study was to determine the mechanical robustness of the human femoral shaft. The geometric properties of the cross sections were measured. The compressive strength, the gamma-ray absorption, and the ash density of the compact bone were examined at 40 points along the shaft. The geometric properties connected with the mechanical robustness increased with the body size. The distribution of the mineral density, the material compressive strength, and the endurable bending moment on the surface of the bone were determined. The density and the strength were great in specimens from the postero-lateral side and in those from the antero-medial to the postero-medial side of the shaft. The calculated endurable bending moment was large on the anterior, the postero-lateral, and the postero-medial surfaces of the middle part of the bone. The anterior side was especially able to endure a large bending moment when the bone had a large moment of inertia of the cross-sectional area in the sagittal direction. The distribution of these mechanical properties could be the functional adaptation of the human femur against external bending forces mainly caused by muscle activity.