A cross-sectional study is proposed to study age related variation in closure of the sacral spines to properly interpret sacral anomalies of closure being studied in other contexts. We propose to test the hypothesis that age of closure is later, and shows greater variation by race and sex, than is generally reported in the literature. We further hypothesize that racial and sexual patterns of closure are governed by differences in the average rate of skeletal maturation in these categories, but that superimposed on this pattern of normal variation are genetic and environmental predispositions to spina bifida in its various manifestations. Our research protocol is designed to test these assumptions as well.