Differential Effect of Gender on the Sizes of the Bones in the Axial and Appendicular Skeletons1

Recent observations suggest that throughout life the size of the vertebral bodies in females is smaller than that in males even after accounting for differences in body size. To confirm these reports and to determine whether similar differences exist in the appendicular skeleton, detailed measurements of the sizes of the vertebrae and the femur were obtained using computed tomography in 30 pairs of prepubertal boys and girls matched for age, height, and weight. Anthropometric parameters as well as gender influenced the cross-sectional area of the vertebrae. Heavier children had greater vertebral cross-sectional area than slender children regardless of gender, and the vertebral bodies were found to be significantly smaller in girls than in matched boys (approximately 11%), both using Student's t test (P < 0.0001) and its multivariate analog, the Hotelling's T2 test (P < 0.0001). In contrast to these findings in the axial skeleton, gender status did not influence the size of the bones in the appendicular skeleton, and neither the cross-sectional area (3.28 +/- 0.84 vs. 3.10 +/- 0.56 cm2) nor the cortical bone area (1.80 +/- 0.37 vs. 1.85 +/- 0.36 cm2) at the midshaft of the femur differed between boys and girls. These values, however, correlated strongly with all anthropometric indexes, and multiple regression analyses indicated that both measurements were primarily related to weight. The results suggest that although increases in mechanical loading associated with growth are the main determinant of the cross-sectional properties of the appendicular skeleton in children, factors other than body mass and related to gender have a significant role in the regulation of the sizes of the bones in the axial skeleton.