Cortical bone mass and geometry: age, sex, and intraskeletal variation in nineteenth-century Euro-Canadians.

Objectives: This study seeks to understand the interaction of cortical bone strength and mass within individuals and across age-groups in male and female adults from a relatively active, long-lived nineteenth-century Euro-Canadian population. Methods: Strength and relative cortical area are measured in paired femora (weight-bearing elements) and metacarpals (manipulative elements) from 139 adults (M = 82; F = 52). Sex and age patterns are tested using linear multiple regression and analysis of covariance. Intra-individual divergence between femora and metacarpals is quantified using the Pearson residual from regression of femur on metacarpal values. Association of residuals with age is tested with curve estimation, factorial analysis of variance and X-2 tests. Results: Strength is maintained but cortical mass declines with age. In females, the slope of cortical mass against age is steeper in the metacarpal than in the femur. However, the degree of divergence between femur and metacarpal within individuals does not increase clearly with age. Conclusions: Age change in bone strength is systemically controlled and homeostatic, but change in bone mass may vary with limb-specific mechanical environment, particularly in females. However, the distribution of within-individual divergence between femur and metacarpal values suggests that idiosyncratic factors, rather than age, have the strongest influence on intraskeletal divergence. Attempts to reconstruct skeletal ageing in past populations may benefit from an approach that models whole-bone integrity, rather than bone mass alone, and that represents age-related variation in both weight-bearing and nonweight-bearing sites. Am. J. Hum. Biol. 23:534-545, 2011. (C) 2011 Wiley-Liss, Inc.