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Getting Kneecaps Back on Track: Biofeedback Doesn't Help

Have you ever stood up to leave a movie theater and had a loud pop and pain in your knee? This is called the "movie sign." It happens when the knee has been bent and is suddenly straightened. For some people, this can happen anytime the knee has been flexed for 15 minutes or more.

The movie sign is common with a condition called patellofemoral pain syndrome. This is a medical term for "pain and symptoms around or behind the kneecap." It happens most often in young adults. The exact cause is unknown, but doctors think it occurs because of the position of the kneecap, or patella.

Normally, the patella moves up and down as the leg straightens and bends. There is an actual track the patella follows as it goes through these motions. Muscles, ligaments, and bone alignment help hold the patella in the middle. Many different problems can cause the patella to get off center, a situation called patellofemoral malalignment. When this happens, patellofemoral pain syndrome can develop. This includes pain, aches, and crunching sounds or "crepitus" when the knee is bent or straightened.

Some of the causes of patellofemoral malalignment include changes in normal knee anatomy, poor function of the surrounding muscles, and tightness in the ligaments that connect to the patella. Sometimes there is weakness or imbalance in the large muscle over the front of the thigh (quadriceps muscle). This muscle is made up of four parts with two major sections: the vastus medialis and the vastus lateralis. When the lateralis (on the outside of the thigh) is stronger than the medialis (the inner part of the front thigh), the patella gets pulled to the outside.

Many studies have tried to find a way to strengthen the weaker medialis muscle. No single method has been found effective. One group of researchers compared doing standard exercises for this condition versus doing exercises plus biofeedback training. They were trying to improve the balance between the lateralis and medialis muscles.

Biofeedback is a way to help patients get better awareness of muscle contractions. It can also help increase the strength of muscle contractions. In this study, electromyographic biofeedback was used. Patches or electrodes were placed on the skin over the quadriceps muscle. These recorded how well the muscle was working. Patients could hear a signal and see the pattern on a computer screen. This showed them how and when the muscle was firing.

Patients used this type of biofeedback to concentrate on getting a maximum muscle contraction. They were told to contract the medialis muscle and hold it for 10 seconds while attempting to quiet the lateralis. Unfortunately, in this study, the biofeedback treatment did not produce better results than exercises alone. Although the medialis showed improved strength with the biofeedback, there was no change in knee function or patellar tracking.

Biofeedback treatment for patellofemoral pain syndrome does not seem to be any better than the standard exercises used for this condition. The added cost and time of biofeedback can be eliminated in the treatment program. Even though this study did not have a positive outcome, researchers can still use the information. Knowing what doesn't help can be as useful as finding out what does help.

References: Nigar Dursun, MD, et al. Electromyographic Biofeedback-Controlled Exercise Versus Conservative Care for Patellofemoral Pain Syndrome. In Archives of Physical Medicine and Rehabilitation. December 2001. Vol. 82. No. 12. Pp. 1692-1695.

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