Our seven-year-old grandson has a partially dislocated hip from cerebral palsy. The parents (our children) don’t have insurance so we have been paying many of the medical bills. We just got a bill for X-rays and now heard today the surgeon wants an expensive CT scan, too. We don’t want to withhold what Jason needs but we can’t help but wonder if this is really a necessary test.

A hip subluxation (partial dislocation) in a child with cerebral palsy is likely going to require surgery. That could be the reason for all the tests. Before trying to rebuild or reconstruct a hip subluxation, the surgeon must map out every detail of the hip itself.

In order to prevent future problems, the surgeon must understand now what went wrong. In other words, why did the hip start to dislocate? And where are the weak or deficient places in the hip socket where the head of the femur has popped out?

These questions must be answered when planning surgery to reconstruct the hip. Otherwise, the same problem can happen again after surgery. There could be instability at the top of the socket (superior direction). This superior deficiency could be more toward the front (anterior) or more toward the back (posterior) part of the hip.

Then again the instability or deficiency could be multidirectional (present in more than one direction). The problem is really more complicated than that. In many cases, normal growth and development of the bones is altered in children with cerebral palsy by the change in muscle pull and biodynamics.

For example, the femur may twist or tilt thus placing the head of the femur in the socket at an angle. Likewise, any change in the shape or orientation of the pelvic bones that form the upper part of the hip socket can have an impact on alignment.

The surgeon must take both the direction of the hip subluxation and the location of the acetabular (hip socket) deficiency into consideration when planning corrective surgery. How is this type of evaluation done? That’s where the testing you are paying for might be needed.

There are three-dimensional CT scans that allow orthopaedic surgeons to see the entire acetabulum (hip socket). The surgeon needs information on direction, depth, and degree of hip dysplasia (shallow socket). The CT scan provides depth and direction but not degree of dysplasia.

Pelvic X-rays may offer a better view to measure something called the acetabular index. The acetabular index is a measure already in use to look at the angle of the acetabular roof. Combining these two tests together (CT scan and pelvic X-ray) makes it possible to get a three-dimensional view of the angle and curve of the roof (top) of the acetabulum (socket).

How will your surgeon use this information? Using the acetabular index will give surgeons a more accurate measure of all the planes of the acetabulum. Taking this measurement in consideration along with other factors such as child’s age, function, and other deformities will help direct surgical choices when reconstructing the dysplastic hip in children with spastic cerebral palsy.