Morphology of the acetabulum in congenital dislocation of the hip. Gross, histological and roentgenographic studies.

At autopsy, the hips of six infants who died soon after birth and had unilateral congenital hip dysplasia were found to have a cartilaginous ridge in the acetabulum which separated the hip socket into two sections. In two of the hips with a moderate degree of dysplasia and in one completely dislocated hip the ridge was formed exclusively by a bulge of acetabular cartilage. In three completely dislocated hips the ridge was formed by a bulge of acetabular cartilage covered by the inverted labrum. The acetabular cartilage showed signs of degeneration whereas the triradiate cartilage was normal. Examination of many newborn infants indicated that hip "clicks" are common and are not diagnostic of hip dysplasia. This diagnosis should be made only when the femoral head slides with a jolt over the acetabular ridge, causing a true positive Ortolani sign. Scattered ossification centers in the acetabular cartilage were seen on the roentgenograms of nearly half of fifty-nine hips with congenital dislocation reduced after the child was two years old, but less frequently in hips reduced at an earlier age.