DEAR MAYO CLINIC:

My 4-month-old daughter has hip dysplasia. One leg is one-half inch shorter than the other. Does this mean she will need a hip replacement in the future?

ANSWER:

Some people born with hip dysplasia eventually require hip replacement. But when the condition is detected during infancy -- as in your child's situation -- effective treatment is often available, significantly decreasing the chances that hip replacement will be necessary in the future.

The hip is a ball-and-socket joint. The top part of the leg's thigh bone (femoral head) is the ball portion of the joint. It fits into an opening (socket) in the pelvis. Hip dysplasia, also called developmental dysplasia of the hip, is a condition present at birth in which the ball of the hip joint is not firmly in the socket. This may happen because the socket is too shallow, the hip joint is dislocated, or the ligaments holding the ball in place are too loose. The exact cause of hip dysplasia is unknown, although there appears to be a familial tendency toward hip dysplasia. The condition is much more common in girls than in boys.

In the most severe cases of hip dysplasia, the hip joint is dislocated, which means the ball of the joint is completely outside the socket. Although that may sound painful, it's not. Hip dysplasia is a painless condition, and most children can function remarkably well, even with a dislocated hip. Hip dysplasia that involves dislocation is often diagnosed soon after birth because a difference in leg length is usually apparent. For your 4-month-old to develop a one-half inch leg length difference, the hip would have to be dislocated.

Treatment of hip dysplasia in infants younger than 6 months is with a soft device (Pavlik harness) that holds the hip joint properly in place. If the joint is displaced only, and the socket is otherwise normal, the harness is typically necessary for about three weeks. If the socket is too shallow or the joint is otherwise unstable, the harness may be needed for up to six months to promote correct development of the joint as the child grows. For 90 percent of babies diagnosed with hip dysplasia, a Pavlik harness successfully corrects the problem.

If the harness isn't effective, or if the child is older than 6 months, a procedure is needed to position the hip joint properly. This may involve gently manipulating the joint into place while the child is sedated (closed reduction), or it may require open surgery in which a surgeon makes an incision in the hip, properly positions the joint and secures it with stitches. Following these procedures, a special cast that extends from the chest to the ankles (spica cast) is required to hold the joint in place.

Children who are adequately treated for hip dysplasia during the first year of life usually don't require additional treatment, and long-term complications are unlikely. The older a child is when a diagnosis of hip dysplasia is made, and the later in life treatment is received, the higher the likelihood of developing early degenerative arthritis in the hip, due to wear and tear of the hip joint.

Delayed diagnosis is more common in mild cases of hip dysplasia because symptoms are usually minimal. Eventually, though, undiagnosed hip dysplasia can cause pain and discomfort, lead to premature wear and tear of the hip joint, and result in arthritis. It is estimated that hip dysplasia is responsible in approximately one-half of adults with arthritis who require hip replacement surgery.

Fortunately, because your child's hip dysplasia was identified early and can be treated during infancy, the risk of long-term problems as a result of this disorder is quite low. -- William Shaughnessy, M.D., Pediatric Orthopedics, Mayo Clinic, Rochester, Minn.

Medical Edge from Mayo Clinic is an educational resource and doesn't replace regular medical care.

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