Age-related changes in female femoral neck geometry: Implications for bone strength

Abstract

Bone strength is a function of both bone mass and its geometric distribution, a factor that is obscured in the conventional bone mineral analysis. Structural geometry is particularly important in areas such as the femoral neck that are exposed to bending loadsin vivo. Here we present results of a study examining age changes in the structural geometry of the female femoral neck derived from dual photon absorptiometry (DPA) data. In a previous study, differences in the aging patterns of males and females over the entire adult age range were demonstrated. In that study, only males showed “compensatory” geometric restructuring of the femoral neck which tended to offset loss of bone mineral with age. In the present study, femoral neck structural properties from 1044 women were examined for aging trends before and after the approximate age of menopause (50 years). Women in the premenopausal age range showed a 4% decline per decade in femoral neck BMD, but no change in the femoral neck cross-sectional moment of inertia (CSMI). This aging pattern is similar to that of males in our earlier study, and in both cases resulted in little or no increase in femoral neck bending stresses. After age 50, however, women show a more rapid decline in femoral neck BMD (7% per decade) accompanied by a decline in CSMI of 5% per decade. These changes result in increases in femoral neck stresses of 4–12% per decade due to the apparent lack of compensatory restructuring to offset the loss of bone mineral. These results shed further light on the age-related mechanisms underlying sex differences in fracture incidence among the elderly. They also argue for the routine use of such structural analyses in any study of age-related osteopenia or the effects of therapeutic intervention on this condition.