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Change in Cortical Bone Density and Its Distribution Differs between Boys and Girls during Puberty

Departments of Orthopaedics (S.A.K., H.A.M.) and Family Practice (H.A.M.), Faculty of Medicine, and School of Human Kinetics (H.M.M.), University of British Columbia, Vancouver, Canada V5Z 1L8

Address all correspondence and requests for reprints to: Heather McKay, Room 588, Department of Orthopaedics, University of British Columbia, 828 West 10th Avenue, Vancouver, British Columbia, Canada V5Z 1L8. E-mail: heather.mckay{at}family.med.ubc.ca.

Concept: Postmenarchal girls and premenopausal women have 3–4% higher cortical bone density (CoD, milligrams per cubic centimeter), compared with postpubertal boys and men, respectively. Females’ denser cortical bone is thought to serve as a calcium reservoir for reproductive needs. However, prospective data are lacking that describe CoD development and bone mineral density distribution during puberty in both sexes.

Objective: Thus, our objectives were to assess maturity and sex differences in the 20-month change of CoD and radial distribution of bone mineral density (RDBMD, milligrams per cubic centimeter) in early-, peri-, and postpubertal girls and boys. Maturity groups were based on change in menarcheal status (girls, n = 68) and pubic hair stage (Tanner) (boys, n = 59). Peripheral quantitative computed tomography was used to measure CoD and RDBMD at the tibial middiaphysis.

Results: The increase in average CoD was 1.9% [22.8 mg/cm³; 95% confidence interval (CI), 10–36], 2.8% (33.8 mg/cm³; 95% CI, 21–47), and 1.5% (55.0 mg/cm³; 95% CI, 17–93) greater in early, peri-, and postpubertal girls, compared with boys, respectively. Analysis of RDBMD revealed that the change in density distribution varied across pubertal groups in girls. Across puberty, all girls showed an increase in the high density midcortical region, whereas only peripubertal girls showed an increase in the lower density subcortical region. A sex-difference in RDBMD change was noted within early and peripubertal groups.

Conclusions: Our findings of sexual dimorphism in CoD development give support to the hypothesis that female bone deposits calcium for reproductive needs by consolidation of cortical bone during puberty.