Changing femoral geometry in growing girls: a cross-sectional DEXA study

In elderly women, a long hip axis length has been shown to increase the risk of hip fracture. However, to date, few measurements of hip geometry have been reported in children and adolescents. The present cross-sectional dual-energy X-ray absorptiometry (DEXA) study of 200 girls aged 3-16 years was undertaken to determine at what age adult hip geometry is achieved and to examine possible influences of anthropometry and body composition on the development of femur axis length (FAL) and femur width (FW) during growth. Adult values for FAL and FW were achieved by age 15 years. Age, height, lean tissue mass, total body bone mineral content (BMC), weight, FW, neck of femur bone mineral density (BMD), and fat were each strongly associated with FAL (p < 0.001), the highest correlations being with age (r = 0.917) and height (r = 0.906). However, after adjusting for age and height, only lean tissue mass, weight, and fat mass remained significantly associated with FAL, suggesting that bone mineral accrual does not influence variance in FAL. Our results also suggested that fat mass and weight per se tended to have greater influence on FW than on FAL in age- and height-adjusted data. Twin studies indicate that 20% of adult hip axis length is associated with environmental factors. We therefore conclude that any environmental effects of physical activity or nutrition on hip geometry must occur before early teen-age years.