Context: The role of sex steroids in bone growth in pubertal girls is not yet clear. Bone biomarkers are indicators of bone metabolic activity, but their value in predicting bone quality has not been studied in growing girls.

Objective: To examine the association of sex hormones and bone markers with bone geometry and density in pubertal girls. Design: 2-year longitudinal study in pubertal girls. Measurements were performed at baseline, 1- and 2-year follow-up.

Setting: University laboratory.

Participants: 258 10-13 yr-old healthy girls at the baseline.

Methods: Peripheral quantitative computed tomography was used to scan the left tibial shaft. Serum 17-estradiol (E2), testosterone (T), their binding globulin (SHBG), osteocalcin (OC), bone-specific alkaline phosphatase (BALP), and tartrate-resistant acid phosphatase isoform 5b (TRACP 5b) were assessed. Data were analyzed using hierarchical linear models with random effect.

Results: E2 was a positive predictor for total bone mineral density (BMD), cortical thickness, and a negative predictor for endocortical circumference (EC), but had no predictive value for total bone cross-sectional area (CSA) or pericortical circumference (PC). T was a positive predictor for total CSA and PC as well as EC, and a negative predictor for total BMD. OC was negatively correlated with cortical BMD (R² = 0.325, P < 0.001).

Conclusions: In pubertal girls, E2 and T have different influences on bone properties at the long bone shaft. The results suggest that at the endocortical surface, E2 inhibits bone resorption during rapid growth and later, after menarche, acts at higher concentrations to promote bone formation. At the periosteal surface, T promotes bone formation, while E2 does not affect it. In addition, OC might be used as a predictor of cortical BMD.