Metacarpal cortical area as an index of bone mass

Abstract

X-rays were taken of the hands of 379 normal subjects aged from 17 to 80 years, using fine grain film. After twelve-fold enlargement by an overhead projector, tracings were made of the outline of both second metacarpals and of their cortices. The total and cortical areas were measured, using a digitizer interfaced to a calculator. There was found to be a significant correlation of cortical area with total area, with different regression equations for males and females. The cortical areas were therefore corrected to a mean male-female total area (788 mm2), using the appropriate equation. The mean total area for all males was 905 mm2 and for females 752 mm2. Though the cortical area was greater for males it was found that after correction for total area the cortical area for males and females aged 20–50 years was similar at 190±21 mm2 (mean±S.D.). After the age of 50 years the corrected cortical area decreased in both sexes; by 75 there was a mean fall of 39% in females and 18% in males. The reproducibility for corrected cortical area was 2.6% for individuals and 1.5% for groups. Compared with the bone mineral analyser this technique is simpler, requires less expensive equipment and gives a better measure of bone size; compared with the simple linear measurements of cortical width it provides greater reproducibility. It is useful as a measure of bone size and bone mass, for observing the course of osteoporosis and its treatment, and for epidemiologic studies.