Electromyographic predictors of residual quadriceps muscle weakness after anterior cruciate ligament reconstruction.

BACKGROUND: Despite the high prevalence of residual quadriceps muscle weakness after anterior cruciate ligament reconstruction, specific predictive factors have not been identified. HYPOTHESIS: Electromyographic analysis is a better predictor of residual muscle weakness than is preoperative strength. STUDY
DESIGN: Prospective cohort study.
METHODS: The quadriceps muscle strength of 37 patients (25 men, 12 women) was measured before reconstruction and 5 weeks and 6 months after surgery. Quadriceps surface electromyographic signals were recorded during all of the strength tests. Integrated electromyographic analysis and median frequency measurements were computed as deficits on the involved side. Patients also performed a single-legged hop test at the 6-month follow-up examination.
RESULTS: The patients had significantly lower strength, integrated electromyographic analysis, and median frequency measurements on the involved side at all three time intervals. The best predictor of the quadriceps muscle strength deficit at 6 months was the combination of the preoperative median frequency deficit and the 5-week postoperative strength deficit. The best predictor of the hop test deficit at 6 months was the combination of preoperative deficits in integrated electromyographic analysis and median frequency.
CONCLUSION: Preoperative electromyographic indices of quadriceps muscle function and early postoperative strength were predictive of residual weakness and impaired function 6 months after reconstruction.