Some babies are born with a dislocation, or lack of fit, between the top of the thigh bone (which is shaped like a ball) and the socket in the hip bone. This occurs in approximately 1 in 700 births, and is more common in girls by a ratio of 4:1. Usually only one hip is affected, but both hips are involved in 25% of cases.
Cause
There is no one cause of congenital dislocation of the hip (CDH). Genetic factors seem to play a part, as it is more common in girls than in boys, and especially in daughters of mothers who themselves had CDH as babies. The posture of the baby in the womb also seems important, so that it is more common in breech presentations (where the baby is born legs first instead of the usual head first).
Clinical features
Often there are no easily detectable signs of CDH in infancy. Sometimes the skin creases in the thighs are asymmetrical. Parents may notice when changing the nappy that one thigh is restricted in its movement, and cannot be laid all the way back on the table. Later, an abnormal position of the leg on the affected side may be noticed, and the leg itself may be shorter than the other due to dislocation. There may be a delay in walking, or the child may walk with a limp or with the pelvis tilted to one side.
During the doctor’s examination of a newborn baby, both hips are carefully checked for any signs of dislocation. Several tests are performed specifically to detect CDH or an unstable hip. On examination of your baby’s hip a faint click may be heard (‘clicky hips’), which may be due only to stretched ligaments and simply requires monitoring. If this click is accompanied by an abnormal movement of the hip, the diagnosis of congenital hip dislocation is likely.
Investigation
A very careful physical examination of both hips should be done in the first few-days of life, and repeated at 6 weeks of age. In experienced hands, this should detect most cases of CDH. Sometimes an X-ray of the hip may be helpful, and ultrasound is being increasingly used
