Roentgenographic parameters of the normal infant hip.

Multiple parameters of hip development were analyzed in 100 children at 3, 6, 9, and 12 months. The acetabular index decreased from 25 degrees in girls and 22 degrees in boys at 3 months to 18 and 19 degrees, respectively, at 24 months. H distance did not vary with age or sex, but D distance increased with increasing age. Measurement of the medial gap was found to be highly variable. Asynchronous appearance of the secondary ossification centers occurred in eight children and was not associated with subsequent abnormal hip joint development. The true acetabular teardrop is not consistently present in these age ranges. The center edge angle increases with age. Shenton's line was difficult to measure and not reproducible.