Age and sex differences in bone density of the second metacarpal in its midshaft cross-section.

On the basis of the midshaft cross-section of the second metacarpal in 102 male and 96 female Japanese, aged 30 to 98 years, age- and sex-related differences of bone mass and density are examined. Bone mass and density are almost always greater in males than in females. Cortical mass and apparent bone density decrease gradually with age after 45 years of age in both sexes. The decreasing rate is about twice as great in females as in males. The sex difference increases gradually with age, especially after the sixth decade. However, true bone density remains almost constant, regardless of age, until the seventh decade in both sexes. The maximum density layer is more deeply located at the radial side than at the ulnar, and also more so in males than in females, corresponding to the differences in cortical thickness. The relative depth of this layer to the bone width is about 15% at the radial side and 12% at the ulnar in males and about 12% and 10% at each side in females, respectively.