The timing of BMD and geometric adaptation at the proximal femur from childhood to early adulthood in males and females: a longitudinal study.

During adolescence, the peak velocity in bone mass accretion preceded the peak velocity of estimated geometry at the hip. Whether this pattern continues into adulthood when maximum values are achieved remains unknown. The purpose of this study was (1) to identify the ages at which peak values of areal BMD (aBMD), cross-sectional area (CSA), and section modulus (Z) occur, (2) to determine the percent of adult peak attained during adolescence, and (3) to determine the relationship between body composition and the timing of the adult peak values. One-hundred and sixty-five (92 females) individuals' aBMD, CSA, and Z values were assessed serially at the narrow neck (NN), intertrochanter (IT), and shaft (S) using hip structural analysis (HSA). Peak bone values and the ages of attainment were assessed using factorial MANOVA. In males, aBMDp (NN 19.4 ± 2.7 years, IT 20 ± 3.4 years, and S 21.8 ± 2.8 years) occurred significantly earlier than CSAp at all sites (NN 21.6 ± 3.2 years, IT 21.1 ± 3.4 years, and S 22.3 ± 3.1 years) and earlier than Zp at the NN (22 ± 3.2 years) and IT (21.3 ± 2.9 years). In females, aBMDp (NN 17.9 ± 2.7 years, IT 18.7 ± 3.5 years, and S 19.7 ± 3.3 years) occurred significantly earlier than CSAp at all sites (NN 20.6 ± 3.6 years, IT 19.4 ± 3.9 years, and S 21.0 ± 3.3 years) and earlier than Zp at the NN (20.7 ± 3.4 years) and S (20.6 ± 3.5 years). The changes in bone mass precede changes in geometric CSA, and this timing may be integral for the development and maintenance of bone strength.