DETERMINANTS OF FEMORAL GEOMETRY AND STRUCTURE DURING ADOLESCENT GROWTH

Our goal was to understand developmental determinants of femoral struc ture during growth and sexual maturation by relating femoral measureme nts to gender and developmental factors (age, pubertal stage, height, and body mass). The bone mineral content of the femur was measured by dual energy x-ray absorptiometry in 101 healthy Caucasian adolescents and young adults, 9-26 years of age. After some simplifying assumption s had been made, cross-sectional geometric properties of the femoral m idshaft were estimated. Two geometry-based structural indicators, the section modulus and whole bone strength index, were calculated to asse ss the structural characteristics of the femur. Femoral strength, as d escribed by these structural indicators, increased dramatically from c hildhood through young adulthood. Regressions were performed between t hese femoral measurements and the developmental factors. Our data show that of age, pubertal stage, body mass, and height, body mass is the strongest predictor of femoral cross-sectional properties, and the cor relation of body mass with femoral cross sectional structure is indepe ndent of gender. A model including all four developmental factors and gender did not substantially increase the accuracy of predictions comp ared with the model with body mass alone. Ln light of previous researc h? we hypothesize that body mass is an indicator of in vivo loading an d that this in vivo loading influences the cross-sectional growth of t he long bones.