Femoral neck width is associated with unique trajectories of age-related hip structural changes and fracture risk within populations of adult women and men.

Osteoporosis management relies heavily on areal BMD (aBMD) to identify women and men with reduced bone strength. We tested the hypothesis that baseline FN external size is associated with different bone-loss and area-gain trajectories that are not reflected in aBMD-decline but have different biomechanical implications. We analyzed data from 4 longitudinal studies with repeated hip DXA scans of women and men over 10-15 yr of follow-up. Changes in FN BMC, area, and aBMD were compared across height-adjusted baseline FN area tertiles using linear models. Fracture risk differences across the tertiles were tested using Cox proportional-hazard models. Women and men with smaller baseline FN area had smaller BMC-declines and greater area-increases over 10-15 yr. In contrast, those with a larger FN area experienced twice the annual BMC-declines but much smaller area-increases. In general, these structural changes were not reflected in aBMD-changes for either sex. The likelihood of fracturing a hip was 2.5 times greater for women and 2.4-4.2 times greater for men in the larger FN area tertile compared to those in the smaller FN area tertile. Unique patterns of age-related structural changes with different biomechanical implications were identified within populations of women and men. These results challenge the general assumption that age-related structural changes are homogenous within a population and question whether aBMD-declines reflect strength-declines consistently among women and men. How these unique patterns of structural change affect the response of women and men to osteoporosis interventions remains to be determined.