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New Way To Predict Need For Surgery For Hip Dysplasia

Posted on: 07/24/2008
Developmental dysplasia of the hip (DDH), previously known as congenital hip dysplasia is a common disorder affecting infants and young children. In this condition, there is a disruption in the normal relationship between the head of the femur and the acetabulum (hip socket). 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 identification and treatment of this problem is important. Treatment allows normal growth to occur. With normal growth of the hip socket, dysplasia is improved. It may even be possible to avoid surgery to correct the problem.

The earlier surgery is done to correct the problem, the better the final results. The trick is to accurately predict which children are going to need surgery. It's best to avoid surgery in children with DDH who don't really need it.

Surgeons from Saudi Arabia think they may have found a new way to predict how things will go. They are using an angle of measurement from X-rays called the acetabular cartilaginous angle (ACA). Results of research using this new measurement are presented in this study.

All children involved had successful closed reduction surgery to correct the problem. Closed reduction means the dislocated hip was realigned in the socket and held in place with a cast. An open incision wasn't needed to accomplish this realignment. The cast called a hip spica goes from waist to toes on the operated side and from waist to above the knee on the uninvolved leg.

After casting for three to four months, each child was placed in a special abduction splint. The splint was worn full-time for six weeks, then only at night for another six to 12 weeks.

Success was measured using X-rays to see if the head of the femur was fully underneath the bony shelf formed by the hip socket. The acetabular cartilaginous angle was used to guide further treatment. This angle is a system of lines drawn on an x-ray to judge the formation of the cartilaginous portion of the acetabulum.

It includes a horizontal line along the bottom of the acetabulum. This is the Hilgenreiner line. Where the Hilgenreiner line intersects a second line determines the angle. The location of the second line differs according to the type of hip deformity that's present.

The authors found that if the acetabular cartilaginous angle was less than 20 degrees, then the hip was very likely to develop fully. There was no further need for surgical repair. Patients with an angle greater than 24 degrees always needed surgical correction. The procedure is called an acetabuloplasty. In this operation, the surgeon uses a bone graft (a piece of bone taken from the child or from a bone bank) to build out the edge of the hip socket. This helps enlarge the hip socket and keeps the head of the femur firmly in the socket.

Of the 234 hips corrected, 100 per cent with an ACA angle 24 degrees or more needed acetabuloplasty. Almost all hips (99.5 per cent) with ACA of 20 degrees or less did not require further surgery. The authors also report that age and acetabular index (AI) are two other important factors or indicators in predicting the need for surgical treatment.

The acetabular index is formed by drawing a horizontal line at the bottom of the pelvis and an angled line from the bottom of the pelvis to the outer edge of the socket. A normal child will have an index of 30 degrees or less. The index decreases until it reaches 20 degrees or less. This usually occurs by age four months in a normal child. An acetabular index above 30 degrees is a sign to begin treatment. The higher the index, the more aggressive the treatment.

In summary, it's difficult to predict whether or not the hip socket will form properly after closed reduction. Early acetabuloplasty has the best results but it's better not to do surgery if it's not really needed. By the time it becomes clear who needs further surgery, the results may be less than optimal.

That's where the three predictive factors (age, acetabular index, and acetabular cartilaginous angle) can help. Using these measures, the surgeon can reliably predict (early on) hips with DDH that will need acetabuloplasty after closed reduction. Results are best if the procedure is done before age four.

References:
Mohammed M. Zamzam, MD, et al. Acetabular Cartilaginous Angle. In Journal of Pediatric Orthopaedics. July/August 2008. Vol. 28. No. 5. Pp. 518-523.

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