Our six-month old baby just had a closed reduction for hip dysplasia. Now we wait and see if it worked. How do they tell if this operation has been successful?

The surgeon will use pelvic X-rays to judge the development of the hip joint. If the child is walking, the X-rays may be taken in the standing position. The surgeon looks for coverage of the femoral head by the acetabulum (hip socket). This means the round head at the top of the femur (thigh bone) is covered by the cup-shaped hip socket.

There are several measurements that can be taken from the X-rays that can help with this decision. For example, the acetabular cartilaginous angle (ACA) 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.

Studies show that if the acetabular cartilaginous angle is less than 20 degrees, then the hip is very likely to develop fully. There is no further need for surgical repair. Patients with an angle greater than 24 degrees very likely need 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.

Another measurement taken from the X-rays is the acetabular index (AI). The AI 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. An acetabular index above 30 degrees is a sign to begin treatment. The higher the index, the more aggressive the treatment.

It’s important that you take your child to all of the scheduled follow-up appointments. The surgeon uses the ACA and the AI to help determine the success of the treatment. If further surgery is needed, early treatment has a better result.