Hip dysplasia in children and babies is a condition where the “ball-and-socket” hip joint is not properly formed.
Generally, the preferred term for this condition is developmental dysplasia of the hip (DDH), as the condition can develop after birth. It is also sometimes called congenital hip dislocation. DDH affects 1-2 of every 1,000 babies born.
The hip joint connects the femur or thigh bone to the pelvis. The top of the femur or femoral head is the “ball” and is located inside the hip socket, which is part of the larger pelvis bone. In DDH, the femoral head does not fit properly inside the cup-shaped hip socket because the socket is too shallow. The femur can even detach or dislocate from the socket in severe cases. The abnormality may be the result of an irregularly shaped femoral head or socket or the ligaments that usually hold the hip joint firmly in place may be stretched.
Either one or both of the hip sockets may be affected, but the left hip is more commonly affected. Babies with DDH require treatment, without which the condition can lead to problems later in life such as a limp, hip pain, and stiff joints. So long as DDH is treated early, children can develop normally, have full-ranging hip movement and lead a normal life.
The extent of looseness in the hip varies between children. In mild cases, the femoral head is simply loose in the hip socket and may move and no longer be centred within the socket. In this case, the femoral head is referred to as subluxatable, which means it may partially, but not completely dislocate. In other cases, the femoral head sits inside the socket, but can easily be pushed out, in which case it is referred to as dislocatable. In the most severe cases, the femoral head is completely detached from the socket and is referred to as dislocated.
The exact cause of DDH is not fully understood, but experts currently believe that the reasons infants may be prone to this condition include the following:
- Family history of the condition – DDH is 12 times more likely to occur in individuals with a family history of the condition.
- Positioning in the womb – If a baby’s position in the womb increases pressure on the hip joints, then the ligaments that support the joint may become stretched. Babies that are in the breech position are also more likely to have less stable hips than those in a normal position.
- Infant’s positioning throughout the first year after birth – Among cultures where infants are positioned with their hips extended on a cradleboard, the rates of DDH are higher than that among cultures where infants are held with the hips apart. Swaddling, where the hips are extended, is therefore not advised during the first few months of life.
- Baby’s response to pregnancy hormones – Around the time of birth, hormones are produced that enable the mother’s ligaments to become lax and stretch more easily, to help the baby move through the birth canal. It is thought that being more sensitive to these hormones than usual can result in a baby having ligaments that are more lax than usual.
When DDH is detected early in life, it can usually be corrected with a splint referred to as a Pavlik harness. If the condition is not diagnosed until later in life when the child is already walking, treatment can be more complicated and the outcomes may be less predictable.
This harness secures the baby’s hips in place, which helps tighten the ligaments surrounding the hip joint, while allowing free movement of the legs. It needs to be worn continuously over a period of several weeks. Eventually, parents are given advice on how to adjust and remove the harness for short periods until it is safe for it to be no longer used.
If a baby is diagnosed with DDH after six months of age or if the harness has failed to work, it is likely that surgery will be required. The most common surgical approach is referred to as reduction, which may be either open reduction or closed reduction. In open reduction, a surgeon makes an incision in the groin area and then gently places the femoral head into the proper position within the hip socket. In closed reduction, the femoral head is also placed correctly in the socket, but no incision is required.
After a reduction procedure, a hip cast needs to be worn for at least six weeks before further checks are carried out, after which it is likely that a cast will be required for a further six week period.