Densitometric study of developing femur

The purpose of this work was to extend to long bones the study on the ossif ication of human fetal skeleton in relation to conceptual age by a quantita tive methodological approach. Postero-anterior scans were performed on 29 d ried fetal femora (from 11.5 weeks of conceptual age to term) 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 (B MD, g/cm(2)). BMD was calculated on a rectangular area corresponding to the total length and minimum width of the shaft. This area was divided into fi ve equal sections along its longitudinal axis in order to estimate the rate of ossification from a spatio-temporal point of view. Our data show that B MC has a high correlation with conceptual age during the whole prenatal lif e, increasing in the third trimester (r greater than or equal to 0.96). Dur ing development, BMD is progressively less correlated with conceptual age ( r = 0.95 in the first half of development, r = 0.68 in the second half), pa rticularly according to a bidirectional gradient from the middle to the pro ximal and distal ends of the shaft. Our findings confirm the data obtained in our previous studies on the ossification of fetal human spines, and sugg est an individual variability in bone density at term of development and pa rticularly at the level of spongiosa, viz. in the areas mostly involved in architectural changes during the morphogenesis of the long bones.