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Ultrasound Studies Provide Two Measurable Angles to Help Predict Treatment Success for Hip Dysplasia

Posted on: 01/27/2010
When a baby is born with all of his or her fingers and toes and looks healthy, everyone gives a big sigh of relief. But babies can be born with unseen conditions like developmental dysplasia of the hip (DDH). All newborns and infants should be screened as early as possible for hip dysplasia to avoid problems later. That's why doctors usually test for it at birth or at the first follow-up appointment with the pediatrician.

In this condition there is a disruption in the normal relationship between the head of the femur (thigh bone) and the acetabulum (hip socket). Sometimes the acetabulum is too shallow or sloping rather than a normal cup shape. It cannot hold the femoral head in place. Hip dysplasia can affect one or both hips. It can be mild to severe. In mild cases called unstable hip dysplasia, the hip is in the joint but easily dislocated. More involved cases are partially dislocated or completely dislocated. A partial dislocation is called subluxation.

Early diagnosis in the newborn and young infant is important. If the problem is not diagnosed and treated early, the soft tissues around the hip start to stretch out. There can be changes in the blood supply to the hip. Sometimes the hip joint tries to form another hip socket called a false acetabulum. Without the proper ligaments, soft tissues, and joint capsule to hold the femoral head in place, the false acetabulum creates even more problems.

The physical examination performed by the pediatrician is the most important early diagnostic tool. One of the special tests used most often to look for signs of an unstable hip is the Ortolani maneuver. This test is designed to detect if the hip is sliding in and out of the acetabulum.

To perform the test, the doctor places the infant on a table in a supine position (on his or her back). The doctor then abducts the hips by moving the bent hips and knees apart. If the hip feels like it can be pushed out the back of the socket, this is considered abnormal. This is a sign of instability in the hip. As the hip is abducted further, the doctor might feel the ball portion (the femoral head) slide forward as it slips back into the socket. This is a positive Ortolani Maneuver and is also a sign of hip instability.

If the test is positive, the child will be watched closely or immediately placed in a special brace called a Pavlik harness. Treatment isn't always required as some children seem to grow out of it. The hip socket is a soft, rubbery cartilage at birth and some children have greater laxity or looseness naturally. This laxity means the hip moves in and out of the socket fairly easily -- just like in the child who has the anatomic changes associated hip dysplasia--but without any actual changes in the bone structure.

The Ortolani test doesn't differentiate between children with true hip dysplasia and those who just have loose hips. Recently, the use of ultrasonography as an imaging tool has come into play with hip dysplasia. Ultrasound testing might also help doctors recognize who has a true case of hip dysplasia and is a good candidate for the harness treatment.

Doctors are also concerned because the harness doesn't always work to put the hip back in place. In fact, it's estimated that four out of every 10 infants aren't helped by the harness. That leads researchers to wonder: is there a way to tell ahead of time which children will benefit from the harness and when it is likely to fail? Are there certain signs or anatomical changes that can be seen early with an ultrasound to help guide treatment?

The results of this study suggest yes and show that babies who test positive for Ortolani sign but fail treatment with the harness actually had a visible reason for that failure. They tested a large number of infants (total of 1,566 hips) and found 228 hips that tested positive using the Ortolani's test. Only those children who had an ultrasound study done within the first four weeks of treatment with a Pavlik harness were included in this particular study. That amounted to a total of 115 hips.

They divided the children in two groups based on treatment results: those who failed the harness treatment and those who were successful. Failure meant the hip did not go back into the socket and further treatment (usually surgery) was required. Going back and looking at the ultrasound studies and comparing the two groups, they found that the failure group had an inverted labrum. The labrum is a rim of fibrous cartilage around the hip socket. It is designed to give the socket a little bit more depth to hold the head of the femur in place and prevent subluxation or dislocation.

Instead of acting as a buttress or barrier to movement, the labrum in the failure group was inverted (turned inward) and blunted (short) and was therefore at an angle that didn't help stabilize the femoral head in the socket. Without this added support, the harness treatment only keeps the hip in its socket while the harness is in place. Once the harness is removed, the hip slides out of the socket.

The authors provided photos of their ultrasound pictures with lines drawn in to show other surgeons how they measured the angles and determined that the abnormal labrum was the problem. Two angles in particular were predictive of Pavlik harness failure: femoral head displacement relative to the labrum (FHD-L) and total femoral head displacement (FHD-T).

Children with an FHD-L of zero degrees (normal relationship of femoral head to the labrum) had successful results with the Pavlik harness. These children probably just had loose cartilage and the head of the femur could slip into the socket easily. They may not have even needed the harness. By the time the harness was removed, the cartilage had tightened up and the hip remained in the socket without the harness.

Children with FHD-T angles less than -30 to -40 all failed treatment with the Pavlik harness. This angle indicates that the femoral head was displaced out and up away from the socket too far to be reduced by positioning with the harness. Additional treatment was needed -- either with a wider hip angle using an abduction brace or with corrective surgery.

In summary, early imaging for all children with a positive Ortolani test might help sort out those who don't really need treatment with the Pavlik harness from those who won't benefit from it and need a different treatment approach. The authors have modified their own treatment of hip dysplasia in several ways as a result of the findings from this study.

First, if an ultrasound study shows an inverted and blunted labrum, they use a greater amount of hip abduction and flexion with the harness right from the beginning. Second if the Pavlik harness doesn't work in the first four weeks, they don't keep using it. They switch right away to an abduction brace, which puts the hips into an even wider position to put the femoral head deeply and firmly into the socket. If the abduction brace isn't successful, then surgery is done to reduce the hip (relocate the hip in the socket).

The authors hope that with additional testing to confirm their findings using the two ultrasound angles will help guide orthopedic surgeons in identifying which children are likely to fail harness treatment and need a more aggressive approach right from the start. If there is a normal relationship between the head of the femur and the labrum (FHD-L angle is zero), the harness has a high probability of success. If the hip is located too far out of the socket (FHD-T is -30 to -40 or more), treatment with the harness is more likely to fail.

References:
Klane K. White, MD, MSc, et. al. Ultrasonographic Findings in Hips with a Positive Ortolani Sign and Their Relationship to Pavlik Harness Failure. In Journal of Bone and Joint Surgery. January 2010. Vol. 92-A. No. 1. Pp. 113-120.

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