Ossification centers of human femur.

The purpose of the present work was to investigate the appearance of ossification centers in human femur by Dual-energy X-ray Absorptiometry (DXA), comparing densitometric data with morphogenetic events. Posteroanterior scans were performed on 31 dried femora (from 11.5 weeks of conceptual age to 1 year of postnatal life) by a Hologic QDR 1000 X-ray densitometer with Ultra-Hi-Resolution software. The results were expressed as bone mineral content (BMC, g) and bone mineral density (BMD, g/cm2). The analyses were performed on a rectangular area corresponding to the minimum width and total length of the shaft. The rectangular area was divided into five equal sections along its longitudinal axis, and BMC was calculated on each section. To distinguish the ossification area of the lesser trochanter with respect to the area of the greater trochanter, the proximal femoral end was divided into two portions, medial and lateral, respectively; BMC and BMD were calculated on each portion. Our data show that the ossification center of the femoral shaft extends prevalently in the proximal direction. A denser area was recognizable on the densitometric images at the level of the lesser trochanter from the 19th week of prenatal life and at the level of the greater trochanter at term. During development, the trends of BMC and BMD are similar in both trochanteric areas, but these parameters are fairly constantly higher at the level of the lesser trochanter. Our findings disagree with the data of the current literature on the postnatal appearance of the trochanteric ossification centers and suggest a different biomechanical interpretation of the secondary ossification of the femur.