Developmental dysplasia of the hip (DDH) is a condition caused by abnormal development of the hip joint, in which the top of the thighbone (femur) does not fit securely into the hip socket (acetabulum). See an illustration of developmental dysplasia of the hip. DDH can affect one or both hip joints. The femur may fit loosely into the hip socket (subluxation) or be completely out of the hip socket (dislocated). If only one hip is affected, it is about three times more likely to be the left hip. Girls are more often affected than boys.

See an illustration of hip anatomy in a child.

Signs of the condition may be present at birth. In rare cases, there are no signs of DDH at birth, but the condition develops in the first few weeks or months after birth. The exact cause of DDH is not known but may be related to the position of the baby before birth, during birth (breech birth), or after birth. It may also be caused by higher-than-expected amounts of the hormones responsible for loosening the mother's ligaments during pregnancy.

A baby with DDH may have:

• No obvious signs of the condition.
• Extra skin folds on the inner side of one thigh when compared with the other thigh. The skin folds do not appear in a symmetrical pattern on each thigh.
• Toes that point out to the side because the muscles of the affected leg pull the thighbone out of the hip joint, allowing the foot to turn out.
• Decreased mobility or flexibility in the movement of the affected hip joint.
• One leg that is shorter than the other.

Sometimes the signs of DDH are not apparent until a child starts to walk. Then the child may:

• Stand with one hip raised higher than the other because one leg is shorter than the other. The shorter leg is on the affected side.
• Walk on the toes of one foot with the heel up off the floor, attempting to accommodate the difference in leg length.
• Walk with a limp.

Treatment for DDH depends on the age of the child, how easy it is to keep the femur in place within the hip socket, and whether any deformities have already developed. Treatment may include use of splints, harnesses, casts, or surgery. Back pain or a breakdown of the hip joint (degeneration of the hip) may develop later in life if this condition is not treated.