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Quadriceps femoris muscle activity in patellofemoral pain syndrome

Department of Kinanthropology, University of Quebec at Montreal, Montreal, Quebec, Canada

Marjorie A. King, MS, ATC, PT

Department of Kinanthropology, University of Quebec at Montreal, Montreal, Quebec, Canada

Richard Lefebvre

Department of Kinanthropology, University of Quebec at Montreal, Montreal, Quebec, Canada

André Pépin, MSc

Department of Kinanthropology, University of Quebec at Montreal, Montreal, Quebec, Canada

To elucidate and attempt to dissociate the two mech anisms, neuromuscular and mechanical, underlying pa tellofemoral pain syndrome, 18 subjects, divided into two groups based on a diagnosis of patellofemoral pain syndrome and the knee Q angle, were studied. The control group was asymptomatic and exhibited a nor mal Q angle (mean, 8.25°), whereas the other group, diagnosed as patellofemoral pain syndrome patients, reported knee pain and had an above-normal Q angle (mean, 21.05°). All subjects were tested for isometric maximum knee extension at 90°, 30°, and 15° of knee flexion while they were seated in a special restraining chair. During testing, surface electromyography at the oblique and long fibers of the vastus medialis, and at the vastus lateralis were recorded along with the knee moment of force. The integrated electromyographic signals associated with the peak torque for all of the vastus muscles, along with the vastus medialis obli quus :vastus lateralis and vastus medialis longus:vastus lateralis activity ratios showed no significant differences between groups nor between the three angles, sug gesting that all vasti measured were consistently active throughout the studied range of motion. This suggests that the neural drive was not affected in the patellofem oral pain syndrome patients. However, when the five patients showing the largest Q angles were isolated, they revealed a significantly smaller vastus medialis obliquus:vastus lateralis ratio when compared to the other group. The same ratio was also significantly smaller at 15° compared to 90°. These results did demonstrate that in advanced cases of patellofemoral pain syndrome the vastus medialis may even be less active relative to the vastus lateralis in the last degrees of extension compared to 90°. Furthermore, one may suggest that in patellofemoral pain syndrome the me chanical disturbances are exhibited first, at which time the vastus medialis atrophy, if present, would have a mechanical origin.

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