Pubertal bone growth in the femoral neck is predominantly characterized by increased bone size and not by increased bone density--a 4-year longitudinal study.

Fragility fractures are correlated to reduced bone size and/or reduced volumetric bone density (vBMD). These region-specific deficits may originate from reduced mineral accrual and/or reduced skeletal growth during the first 2 decades of life. Before pathological development can be defined, normal skeletal growth must be described. To evaluate growth of bone size, accrual of bone mineral content (BMC), areal bone mineral density (aBMD) and vBMD in a population-based cohort, 44 boys and 42 girls were followed by annual measurements from the age of 12 to 16 (attendance rates 90-100%). Segmental bone length, bone width, BMC, aBMD and vBMD were measured by dual-energy X-ray absorptiometry (DXA). Data were compared with predicted adult peak, as determined in 36 men aged 27.7+/-4.6 years and 44 women aged 26.8+/-4.9 years. Growth in width of the femoral neck precedes accrual of BMC in the femoral neck in both genders up to age 15. The girls were at all ages closer to their predicted adult peak in both bone width and BMC compared with the boys except in the femoral neck. As femoral neck vBMD had reached its predicted adult peak already at 12 years in both genders, the increase in femoral neck BMC and femoral neck aBMD from age 12 to 16 was most likely to be explained by the increase in bone size. In boys the peak velocity growth was recorded at ~14 years for BMC, height, width and lean mass. Growth from the age of 12 to 16 seems to build a bigger but not a denser skeleton in the femoral neck.