Age-related changes in bone density, geometry and biomechanical properties of the proximal femur: CT-based 3D hip structure analysis in normal postmenopausal women.

The geometry as well as bone mineral density (BMD) of the proximal femur contributes to fracture risk. How and the extent to which they change due to natural aging is not fully understood. We assessed BMD and geometry in the femoral neck and shaft separately, in 59 normal Japanese postmenopausal women aged 54-84 years, using clinical computed tomography (CT) and commercially available software, at baseline and 2-year follow-up. This system detected significant reductions over the 2-year interval in total BMD (%change/year = -0.900 ± 0.257, p < 0.0005), cortical cross-sectional area (CSA) (-0.800 ± 0.423%/year, p < 0.05) and cortical thickness (-1.120 ± 0.453%/year, p < 0.01) in the femoral neck. In the femoral shaft, cortical BMD decreased significantly (-0.642 ± 0.188%/year, p < 0.005). Regarding biomechanical parameters in the femoral neck, the cross-sectional moment of inertia (CSMI) and section modulus (SM) decreased (-1.38 ± 3.65%/year, p < 0.01 and -1.37 ± 2.96%/year, p < 0.005) and the buckling ratio (BR) increased significantly (1.48 ± 4.81%/year, p < 0.05), whereas no changes were found in the femoral shaft. The distinct patterns of age-related changes in the geometry and biomechanical properties in the femoral neck and shaft suggest that improved geometric measures are possible with the current non-invasive method using clinical CT.