Picturing a Tilted Kneecap

Patients with patellofemoral pain syndrome (PFPS) know a thing or two about knee pain. In their case, it’s often the sideways tilt of the kneecap (patella) that causes pain and other symptoms. Teenagers, athletes, and soldiers are the most likely to suffer this condition.

PFPS can be diagnosed with imaging studies such as CT scans or MRI. X-rays don’t always show it because the knee has to be completely straight or just slightly bent to see the problem. But X-rays cost much less than CT or MRIs. X-rays are also easier and faster than other methods of imaging.

Canadian researchers tried using a new X-ray system to look at the knee. Measures of patellar tilt, position, shape, and height were made using a specific type of X-ray system. This new machine is designed to show as little distortion as possible. The knee was X-rayed in 35 degrees of flexion.

Two groups of military subjects were X-rayed. One group had PFPS. The other group was similar in age, years of military service, and gender, but had no knee problems. The authors report no difference in X-ray measurements taken between the two groups. It didn’t matter if the quadriceps muscle was contracted or not.

The authors conclude that the new X-ray system isn’t a useful tool to diagnose PFPS when the knee is flexed at 35 degrees. The knee is bent too much to show any alignment problems. Further study is needed.