Not-So-Stimulating Study on Kneecap PainScientists sit up and take notice of research results when a study is randomized, controlled, and double-blinded. That means there are two groups of subjects. Each person is randomly placed in a group, and no one knows what group they are in. This is the first study of this type looking at the use of electrical stimulation (ES) for patellofemoral pain syndrome (pain where the kneecap meets the thighbone).
ES is used to make a muscle contract without the subject's voluntary contraction. A new type of ES has a mixed-frequency pulse that increases both muscle endurance and power. The older, more traditional ES increases one or the other, but not both at the same time.
These two types of ES were used on 80 patients at home. Everyone had muscle stimulation one hour daily for six weeks (42 sessions). The results were compared using pain, size of muscle, and strength as measures of outcome. Knee flexion was measured by having the patients squat as far as possible before having knee pain.
The authors found no difference in results between the two ES units. Patients in both groups showed improvement in strength, function, and pain levels. Knee flexion improved equally in both groups. A small difference was seen in muscle size.
The researchers offer several possible explanations for these results. They suggest that pain may be reduced when muscle strength improves because the kneecap can track up and down better. A second explanation may be that the ES blocks pain signals by entering a different signal along the same nerve pathway.
Since the patients reported less pain several hours later, it was thought that the change occurred because of the effect of the ES on the muscles rather than from blocking nerve signals. In any case, the effects of ES were the same with both types of frequency. One wasn't better, or worse, than the other.
Michael J. Callaghan, PhD, and Jacqueline A. Oldham, PhD. Electric Muscle Stimulation of the Quadriceps in the Treatment of Patellofemoral Pain. In Archives of Physical Medicine and Rehabilitation. June 2004. Vol. 85. No. 6. Pp. 956-962.
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