Femoral neck shape and the spatial distribution of its mineral mass varies with its size: Clinical and biomechanical implications

Images from micro-CT scanning show that the FN cross-sectional shape resembles an ellipse with the long axis and the maximum moment of inertia (Imax) oriented in the supero-inferior direction, and the cortical mass concentrated inferiorly. The larger the cross section, the more elliptical the shape, and the greater the Imax supero-inferiorly, while Imin (in the antero-posterior direction) remains relatively constant. The shape, spatial distribution of bone, and moments of inertia are likely to be adaptations to bending moments during bipedalism. Assuming the FN cross section approximates a circle or square produces errors in FN depth, volume, vBMD, and geometric indices of bone strength. Studies are needed to determine the effects of age, sex, and race on FN size and shape in health and disease.