Failure of voluntary activation of the quadriceps femoris muscle after patellar contusion

Study Design: Descriptive study of phenomenon. Objectives: To determine the extent of failure of voluntary activation of t he quadriceps femoris muscle in patients early after patellar confusion. Background: Pain and effusion are related to the presence of quadriceps inh ibition. We hypothesized that patients with patellar contusions would be un able to fully recruit their quadriceps muscles and that the activation defi cit would be associated with self-repel? measures of function. Methods and Measures: Sixteen patients who had sustained a unilateral patel lar contusion fewer than 4 months prior to testing participated in the stud y (7 men, 9 women; mean age = 30.0 +/- 11.6). Subjects completed a self-rep ort questionnaire to assess knee function and performed an isometric burst superimposition test on the involved and uninvolved quadriceps at 60 degree s of knee flexion. The subjects were assigned to 2 groups according to the presence (n = 5) or absence (n = 11) of quadriceps inhibition. Results: Sixty-nine percent of the subjects tested were able to fully activ ate their quadriceps. Both groups had a decreased knee extensor force on th e involved side compared to the uninvolved, but the group with inhibition h ad a lower side-to-side percentage of knee extensor force (mean = 65.5% +/- 18.9) than those without inhibition (mean = 85.5% +/- 16.4). Conclusion: Early after patellar contusion, approximately one-third of the patients demonstrated quadriceps inhibition. According to our working hypot hesis, the majority of the patients tested should have demonstrated inhibit ion. Quadriceps inhibition was not associated with the activities of daily living, sports activity, or global rating scales n this study. Decreased vo litional quadriceps force production (the hallmark of inhibition) was the o nly variable that discriminated patients with patellar contusion who had in hibition from those who did not.