Age, sex and bilateral variability in cortical bone loss and measurements of the second metacarpal.

Bilateral hand-wrist radiographs were obtained from 176 female and 448 male adult participants of the Baltimore Longitudinal Study of Aging (BLSA). Between-age group analysis revealed no change with age in total width (TW) of the second metacarpal but a significant increase in medullary width (MW) along with decreases in per cent cortical area (PCA) and combined cortical thickness (CCT) in both sexes. The magnitude of change was greater in females compared to males after the fifth decade, suggesting an interaction of the female climacteric with those processes causing bone resorption at the endosteal surface. Those women currently on estrogen exhibited significantly higher PCA and CCT and lower MW for their respective ages compared to non-users. In females, body mass index (weight/height2) was also associated with increased PCA and CCT and decreased MW. In general, the second metacarpal was longer and larger for right hands compared to left, and for males compared to females. Right hand dominance further enhances growth of the right second metacarpal so that bilateral differences for TW, MW, CCT and LEN become statistically significant. Conversely, left hand dominance promotes growth of the left metacarpal so that none of the variables studied showed significant bilateral differences.