The hip is a ball-and-socket joint. In a normal-functioning hip, the rounded top of the thighbone, or femoral head, rests comfortably in the acetabulum (the cup-like hipbone socket).
In mild cases of DDH, the femoral head moves back and forth slightly out of the socket, causing a child to have an unstable hip. In more serious cases, the head becomes dislocated, moving completely out of the socket, but sometimes can be put back in with pressure. In the most severe cases, the femoral head may not even reach the socket.
The causes of DDH aren't completely understood, but experts think various factors are involved. These include cramping or abnormal positioning of the fetus in the womb, and softening and stretching of the hip during delivery in response to the hormones that relax the mother's ligaments for labor and delivery. After birth, DDH can be caused by swaddling a newborn too tightly around the hips.
DDH usually does not cause pain early on and typically affects only one side of the body, most often the left. Doctors look for DDH while checking the hip joints during routine infant checkups. A doctor who feels a "clunk" or hears a "click" in the hip during the exam probably will send the baby for a hip ultrasound to check for DDH. Older children with DDH may have different leg lengths or limping.
Infants are often treated with a harness that holds the femoral head in the socket until the hip is stable. Older children may need surgery to realign the affected hip.
Keep in Mind
Developmental dysplasia of the hip may happen no matter how you try to prevent it, but if it's recognized early and treated, most children will develop normally and have no related problems. Mild cases may correct themselves in the first few weeks of life, but more serious cases that are not treated can result in legs of uneven length in adulthood, which can lead to a limp or waddling gait, back and hip pain, and overall decreased movement.
All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.