The anatomy and pathology of congenital dislocation of the hip.

At least 1 per cent of all newborn infants in the United Kingdom have CDH (Fig 10). Among these infants, approximately 85 per cent are normally formed and 15 per cent malformed. Among the normally formed infants, 90 per cent of the CDH are of the Grade 1 type, and 10 per cent of Grades 2 and 3. Such infants have a perinatal mortality of about 5 per cent. In contrast, among the malformed infants, about 50 per cent are CDH Grade 1, and 50 per cent Grades 2 and 3; their perinatal mortality is around 70 per cent. In other words, a much higher proportion than usual of the severe grades of CDH are found among the infants with a high perinatal mortality.