Age-Related Changes in Whole-Bone Structure and Strength

We review data on age-related changes in bone geometry of relevance to whole-bone strength, as well as the limited data on changes in strength. Consistently across many sites, women have bones that are smaller (by 15–30 %) than age-matched men, and thus are weaker. In both women and men, modest periosteal expansion of the diaphysis occurs throughout life, but this is accompanied by a faster rate of medullary expansion, especially in women. The net result is an age-related decrease in cortical bone at most sites in women, but negligible changes in men. At metaphyseal sites there is also modest periosteal expansion as well as endosteal expansion and net cortical bone loss. But the dominant change with aging is decreased trabecular bone density, with most studies showing greater rates of decline in women than men. These effects are especially pronounced at the proximal femur and vertebra. Changes in whole-bone strength with aging are less well documented. Available data (from mechanical tests and computer models) suggest modest declines in diaphyseal strength in women but not men, and much greater declines in strength of the proximal femur and vertebra. Women and men appear to lose proximal femur strength at similar rates, although the decline starts earlier in women. Also, both women and men lose vertebral strength with aging, with some data indicating a faster decline in women but other indicating equivalent rates of decline. In conclusion, there are important age-related changes in bone structure and density that affect whole-bone strength. Additional studies measuring whole-bone strength with aging are needed.