A sonographic study of perinatal hip development: from 34 weeks of gestation to 6 weeks of age.

A sonographic study of perinatal hip development was performed by consecutive measurement of Graf's alpha and beta angles in fetal and newborn hips. The study group consisted of infants with sonographically normal hip findings at birth. Forty fetuses were examined by fetal hip sonography at 34, 36 and 38 weeks of gestation. Postnatally, hip sonography was performed in the first and sixth week of age. Maturation curves of the bony (alpha-angle) and cartilaginous (beta-angle) acetabular roof from 34 weeks of gestation to 6 weeks of age were established. Prenatally, the mean alpha-angles were above the level that corresponds to a mature hip joint. A significantly higher value of the mean alpha-angles was found after birth. The mean beta-angles of the fetuses did not differ from those of the newborns. Our results revealed that the fetal hip joint is sonographically mature at 34 weeks of gestation. Further progression of hip development occurs around term.