Age changes in geometry and mineral content of the lower limb bones.

Subperiosteal expansion and increase in second moments of area with aging of eleven femoral and tibial cross-sections are documented in a large archaeological sample from the American Southwest. In contrast to these geometric changes, we found little change with age in bone mineral density measured using photon absorptiometry. Thus, the most significant structural changes with age in bone appear to involve its geometry and material characteristics other than its density. Variation in age-related geometric remodeling between cross-section locations and populations may be caused by differences in mechanical stress and strain levels in vivo in the lower limb.