Functional performance is associated with both knee extensor and flexor muscle strength in patients scheduled for total knee arthroplasty: A cross-sectional study.

OBJECTIVE To determine whether muscle strength in patients scheduled for total knee arthroplasty is: (i) strongly associated with both measured functional performance and patient-reported measures; (ii) more closely associated with functional performance when measured during concentric than during isometric contractions; and (iii) more strongly related to the 30-s chair stand test than to the timed-up-and-go and walking measures. DESIGN Cross-sectional-study. PATIENTS Fifty-nine patients (36 women, 23 men), mean age 70.4 years. METHODS Associations between muscle strength, measured functional performance, and patient-reported measures were calculated. RESULTS Both knee extensor and knee flexor strength were associated with performance-based measures. In general, concentric knee flexor muscle strength was more strongly associated with functional performance than was isometric knee flexor strength. Concentric and isometric knee extensor strength were of equal importance. The 30-s chair stand test was better than the timed-up-and-go and the walking tests at determining muscle strength. CONCLUSION Future rehabilitation programmes should include both the knee extensor muscles and the knee flexor muscles in order to improve functional performance. The 30-s chair stand test is a valid and clinical relevant proxy measure of knee extensor and knee flexor muscle strength.