A noninvasive measure of physical maturity as a predictor of bone mass in children

Objective: The purpose of this study was to describe the accumulation of wh ole body bone mass in a longitudinal study of prepubertal boys and girls us ing Roche's physical maturity index as a measure of developmental age. Methods: We measured 561 children (39% white, 61% African-American) from a suburban school district, representing an ethnically mixed, middle-class co mmunity adjacent to Detroit. Anthropometric measures taken for the present study included recumbent length (cm), stature (cm), weight (kg), whole body bone mineral content (WBBMC in g) and a noninvasive measure of physical ma turity (PM%). PM% was calculated from published formulae derived from data from the Fels Longitudinal Study, using recumbent length, weight, midparent al stature, age, and age- and gender-specific regression coefficients. Results: At average age 9.9 (+/-0.6) years, there were no significant gende r differences in stature, recumbent length, weight, or WBBMC in either ethn ic group. Average PM for girls was significantly greater than that for boys within each ethnic group. There were no significant ethnic differences in PM in either gender. Stature and WBBMC were significantly different in the two ethnic groups for both boys and girls. Regressions of WBBMC on PM and c hronological age indicated that PM explained more of the variance in WBBMC than did age (r(2) ranging from 0.28 to 0.75 for PM versus 0.01 to 0.06 for age). In the case of African-American boys, r(2) was similar (0.09 for PM and 0.06 for age). Conclusions: PM is a useful, noninvasive measure of developmental age that is significantly correlated with bone mass in children. Our study also indi cates that PM is a better predictor of WBBMC than chronological age. Becaus e PM can be calculated without using invasive and potentially expensive met hods, PM may be useful in some clinical as well as research settings.