Dimensions and Volumetric BMD of the Proximal Femur and Their Relation to Age Among Older U.S. Men

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Abstract
We measured femoral neck and shaft dimensions and volumetric BMD with QCT. Relations of these measures to age were quantified in a cross-sectional study among 3358 men 65-100 years old. Relations of femoral neck dimensions and vBMD to age differed from those in the shaft, indicating that patterns of bone modeling and remodeling in the neck and shaft are distinct. Little is known about population variation in dimensions and volumetric BMD of the proximal femur or the relation of these measures to age among older men. In a cross-sectional study, dimensions and volumetric BMD (vBMD) in the femoral neck and shaft were obtained from QCT scans among 3358 men 65-100 years of age in the Osteoporotic Fractures in Men cohort. Total bone size and size of the cortical and medullary compartments were measured with volumes in the femoral neck and with areas in the shaft. We quantified distributions of these measures and examined their relations to age with multivariable linear regression. Population variation in femoral neck and shaft dimensions and vBMD was substantial. In the femoral neck, total volume was minimally related to age, whereas cortical volume was 5% smaller and medullary volume was 10% larger (both p < 0.0001) in the oldest (85+ years) compared with the youngest (65-69 years) men. Across these ages, the percent of cortical bone declined from 46% to 42% (p < 0.0001). Integral and trabecular vBMD were 9% and 22% lower, whereas DXA femoral neck BMD was 4% lower, in the older men. Neck cortical vBMD was unrelated to age. In the shaft, cross-sectional area and medullary area were 9% and 22% larger, respectively, in the oldest men (both p < 0.0001), but cortical area was unchanged with age. The percent of cortical bone declined from 69% to 65% across these ages (p < 0.0001). Shaft cortical BMD was 4% lower in the older men (p < 0.0001). There is substantial diversity of femoral morphology and vBMD among older U.S. men. Patterns indicative of modeling and remodeling in the femoral neck were distinct from those in the shaft. Notably, changes in periosteal and endosteal dimensions that underlie cortical thinning appear to differ in the neck and shaft.