Our hip joints are designed so that we can move our legs in many directions — forward, backward, side to side and positions in between. In order for our legs to move in so many directions, the hip joint must be shallow. Our thigh bone (femur) is held in the hip socket by a lot of ligaments and tendons.
Babies and young children are very flexible. Their joints, ligaments and tendons are very stretchy. A newborn has an immature, shallow hip joint with very stretchy ligaments and tendons. Because of all this flexibility the top (head) of the thigh bone (femur) may not sit in the shallow hip socket the way it is supposed to. Or, it may sometimes be in the right position, but slip out of position easily.
If a baby's thigh bones don't stay in the hip socket the way they are supposed to, the hip joint won't develop properly as the baby grows and matures. If the abnormal placement of the thigh bone in the hip socket isn't discovered and treated, a baby may grow into an adult with a very abnormal walk that can't be treated.
If the abnormal thigh bone position is discovered early, the abnormality can be treated and cured completely. This is the reason that pediatricians are fanatical about checking your baby's hip joints over and over. Most pediatricians routinely check hip joints until the baby is at least six months old.
If you are told your baby has dislocating hip joints, likely the only treatment at first will be to put double diapers on him. The extra diaper helps to hold his legs apart, so the thigh bones poke out from the hips in a "frog leg" sort of position. This is the correct position for the thigh bone to be in the hip socket.
Having dislocated hips is not painful to the baby. Changing his diapers and moving his legs around will not hurt him. This is probably why the condition is missed, unless the baby's doctor looks for it.
Within two or three weeks, your baby's hip joints will be evaluated by a pediatric bone specialist (orthopedist). The treatment will depend on what the specialist finds.
Thanks to Janelle Aby MD, Stanford School Of Medicine, Newborn Nursery, and Lucille Packard Children's Hospital for the use of occasional photographs.