Bone Abstracts

The regions of the proximal femur that are at greater risk of structural failure during a fall are those with less adaptive protection promoted by mechanical loading of the activities of daily living. Considering the associations between bone geometry of the proximal femur with bone fracture risk, we intended to examine how geometrical characteristics of the proximal femur (FNL, femoral neck length; FNW, femoral neck width; NSA, neck shaft angle) moderate the effect of mechanical loading on proximal femur bone mineral content (BMC). For this purpose, a parameterized 3-D finite element model of a reference femur (FNL: 54 mm; FNW: 30.6 mm; NSA: 116°) was incrementally adjusted to adopt physiological ranges at FNL (44–69 mm), FNW (29.0–32.6 mm), and NSA (106–131°), yielding a set of femora with different geometries. The bone mineral distribution pattern for each femur was obtained with a bone remodelling model, where a global self-adaptation of bone is optimized in order to achieve the stiffest structure from mechanical loadings associated with gait. In this model bone tissue is formulated as an orthotropic, porous and linear elastic material. Results showed that robust femoral necks (the ones with bigger FNW:FNL ratio) were associated with less BMC at femoral neck, while increased NSA promoted bone mineral distribution patterns where Ward’s area (femoral neck region with the lowest density) was in a more superolateral location. Comparatively to the reference femur it were predicted changes up to 10, 11 and 23% at the femoral neck BMC due to isolated geometric variations (between the reference and the highest range’s value) in FNL, FNW and NSA, respectively. In conclusion, proximal femur geometry seems to moderate the influence of mechanical loading associated to gait in bone mineral distribution at the femoral neck, producing structural differences that may account for structural failure during a fall.

This work was funded by Portuguese Science and Technology Foundation (PTDC/DES/115607/2009).