Human proximal femur bone adaptation to variations in hip geometry.

The study of bone mass distribution at proximal femur may contribute to understand the role of hip geometry on hip fracture risk. We examined how bone mineral density (BMD) of proximal femur adapts to inter individual variations in the femoral neck length (FNL), femoral neck width (FNW) and neck shaft angle (NSA). A parameterized and dimensionally scalable 3-D finite element model of a reference proximal femur geometry was incrementally adjusted to adopt physiological ranges at FNL (3.90-6.90cm), FNW (2.90-3.46cm), and NSA (109-141º), yielding a set of femora with different geometries. The bone mass distribution for each femur was obtained with a suitable bone remodelling model. The BMDs at the integral femoral neck (FN) and at the intertrochanteric (ITR) region, as well as the BMD ratio of inferomedial to superolateral (IM:SL) regions of FN and BMD ratio of FN:ITR were used to represent bone mass distribution. Results revealed that longer FNLs present greater BMD (g/cm(3)) at the FN, mainly at the SL region, and at the ITR region. Wider FNs were associated with reduced BMD at the FN, particularly at the SL region, and at the ITR region. Larger NSAs up to 129° were associated with BMD diminutions at the FN and ITR regions and with increases of the IM:SL BMD ratio while NSAs larger than 129° resulted in decrease of the IM:SL BMD ratio. These findings suggest hip geometry as moderator of the mechanical loading influence on bone mass distribution at proximal femur with higher FNL favoring the BMD of FN and ITR regions and greater FNW and NSA having the opposite effect. Augmented values of FNL and FNW seem also to favor more the BMD at the superolateral than at the inferomedial FN region.