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Predicting Results of the Pavlik Harness for Developmental Dysplasia of the Hip

Posted on: 09/10/2009
Infants under the age of six months are treated for developmental dysplasia of the hip (DDH) with a Pavlik harness. The idea is to take a child with a poorly formed hip socket or dislocated hip joint and position the head of the femur (thigh bone) right in the hip socket. Then hold it there until the joint forms properly. That's where the Pavlik harness comes in. This soft harness positions and holds the infant/child with the hips bent or flexed and abducted (leg apart).

Studies show that this conservative method of treatment works about 79 to 96 per cent of the time. But that's a pretty broad range of success. The authors of this report asked the question, Why did the children in the 96 percentile have a successful response to the harness? Are there some specific predictive factors like age or gender that make the difference?

To find out what they could about possible predictive factors of success or failure of the Pavlik harness, they reviewed the records of over 200 children younger than six months treated this way. They compared children who had a successful reduction (placing the hip back in the socket after being fully dislocated) or subluxed (partial dislocation) to those who failed to achieve adequate reduction.

They took it one step further, too and also looked at the children who developed avascular necrosis (loss of blood supply to the head of the femur). They hoped to find factors that might predict which children would develop AVN. The harness can be tightened too much, pulling the legs apart too much. Too much force into abduction can block the blood supply to the femoral head causing loss of blood flow and necrosis. This is a serious complication that can prolong the treatment of the hip and may lead to other problems. In the general population of children with developmental dysplasia of the hip, anywhere from zero to 22 per cent develop avascular necrosis. In this study, 16 of the children who had a successful hip reduction with the harness still went on to develop necrosis. That's about a nine per cent rate.

The goal in finding predictive factors of failure in the conservative treatment of developmental dysplasia of the hip is to identify children who will benefit from therapy with the harness versus those who won't be helped. No sense using a treatment that you know right from the beginning won't work. It's also important to single out those children who might develop necrosis and be proactive in treatment. Necrosis can lead to deformity and even death of the bone. Where does one begin with a project like this?

Well, the authors reviewed the literature to find the results of other similar studies and see what they used for possible predictive criteria. The child's age, gender, side of the hip dysplasia, severity of the dislocation, and ability to reduce the hip before treatment are clearly the most commonly used factors. But in this study, they chose two additional factors: amount of hip abduction (leg moved away from the midline) and distance of the femoral head from the hip socket (as measured by X-rays). In fact, two separate X-ray measures were used: how far the femur was displaced proximally (up toward/past the hip socket) and how far the femur was displaced laterally (away from the midline).

Since this study was a retrospective study (taking a look back using medical records), they excluded (left out) anyone who did not have before and after X-rays, children with a neuromuscular condition causing the problem, and families that didn't complete the treatment as instructed. With a retrospective study, it's also possible to calculate how long each child wore the Pavlik harness and how long it took to reduce the hip. This type of information can help orthopedic surgeons advise patients on how long to keep the harness on the child and when to give up trying to get good results with this treatment tool.

Physical exam, X-rays, and ultrasound were used to tell if the hips were reduced and/or if avascular necrosis had developed. The children were checked by physical exam every few days at first for a sign that the hip had slipped back into the socket where it belonged. There's a specific test for this called the Ortolani maneuver. The overall rate of successful reduction with the harness in this patient group was almost 82 per cent. Most of the infants responded to the harness within one or two weeks. They were re-checked every two weeks for two months and then every month after that.

An analysis of all the variables considered showed that age at the time of treatment was not a predictor of failure. This was true so long as the child was younger than six months when use of the harness was started. Having a bilateral condition (present in both hips) was a predictor of harness failure. Children with developmental dysplasia in both hips were six times more likely to fail to get reduction of the hip using the harness when compared with children who had only one hip involved.

The starting position of the hip (as seen on X-ray before treatment) was a negative predictive factor. In other words, the farther the hip was from the socket, the less likely it would reduce with the harness and then remain stable in the hip socket. Of the two directions tested (hip displaced proximally/upwards versus hip displaced laterally/away from the socket), reduction was more likely to fail using a Pavlik harness when proximal displacement was a bigger problem.

One other factor that helped predict who would have a failed versus successful response to the Pavlik harness was how far the child's hips would abduct (move away from the midline). Loss of hip abduction is usually a sign of an adduction contracture. Contracture means the muscle is so tightly contracted, the leg can't move (or moves minimally). The fact that the hip could not be reduced manually by moving the leg into a flexed and abducted position before treatment had no bearing on the success of the harness to accomplish reduction over time.

And finally, even though one-third of the children with developmental dysplasia of the hip had a family history of this condition, family predisposition was not a predictor of treatment success with the Pavlik harness. In other words, having a family history of dysplasia didn't necessarily mean treatment would fail.

Taking a look at all the data, the authors concluded that the strongest predictor of harness failure was the proximal distance of the femur from the hip as seen on X-rays. The most reliable predictor of avascular necrosis was the presence of a severe hip adduction contracture (unable to move the affected leg away from the other leg).

What does this information mean in terms of treatment? Basically, although the Pavlik harness is safe to use, it isn't always effective. The more severe the dislocation and the tighter the muscles around the hip are, the more likely it is that treatment with the harness will fail. Consideration may be given for other treatment first (e.g., possibly surgery to release tight muscles or traction to pull the femur down) before applying the harness. Children with dysplasia in both hips are also less likely to benefit from a Pavlik harness. Children who get a good reduction but then develop avascular necrosis pose a real treatment challenge.

References:
Hiroshi Kitoh, MD, et al. Predictive Factors for Unsuccessful Treatment of Developmental Dysplasia of the Hip by the Pavlik Harness. In Journal of Pediatric Orthopaedics. September 2009. Vol. 29. No. 6. Pp. 552-557.

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