Patellofemoral pain syndrome: the possible role of an inadequate neuromuscular mechanism.

Abstract

The patellofemoral pain syndrome is described by a great number of papers as a pathology related mainly to the knee extensor mechanism. However, this knee problem may have an influence on the other joints of the lower extremity. To explain the interdependence between joints of the lower extremity, the support moment concept was used as a framework for the present study. Based on this concept we hypothesized that patellofemoral pain syndrome subjects reduce the stress on their painful patellofemoral joint by decreasing the use of the knee extensor muscles during functional activities. In order to achieve the same support moment, a smaller contraction of the knee extensors could be compensated by an overuse of the hip extensors and ankle plantarflexors. The aim of this study was to verify these compensations in a strenuous functional activity for the knee by comparing 11 subjects having a patellofemoral pain syndrome with 11 normal subjects. Three squat tests were performed:NATURAL, IMPOSED, and TIP TOES. The results obtained in the tip toes test indicated that patellofemoral pain subjects have: (a) a significantly greater knee extensor moment, and (b) a significantly lower hip extensor moment as compared to the normal. A greater straightening of the trunk was observed on patellofemoral pain syndrome patients during the tip toes test as compared to the other tests. Contrary to the expected hypothesis, the patellofemoral pain subjects did not show a strategy tending to decrease the knee extensor moments. In fact in the squat test on tip toes, the subjects affected by a patellofemoral pain syndrome overused the knee extensor muscles.