Isometric muscle force measurement for clinicians treating patients with osteoarthritis of the knee

OBJECTIVE: To evaluate the discriminant validity and, for clinicians, the test-retest reliability of isometric force in patients with knee osteoarthritis (OA). METHODS: Mean isometric muscle strength data collected for 113 patients with knee OA were compared with published normative data for 131 asymptomatic subjects. RESULTS: Patients with knee OA, ages 60-79 years, could attain only 40-53% of the knee extensor force and 35-46% of the knee flexor force generated by their age- and sex-matched peers. One-week test-retest intraclass correlations ranged from 0.79 to 0.95. Random measurement error demonstrated a favorable "signal-to-noise" ratio. CONCLUSION: The similar decrease in knee extensor and knee flexor strength demonstrated by patients with knee OA compared with their age- and sex-matched asymptomatic peers suggests that strategies should be directed at both muscle groups to optimally limit joint damage. Isometric muscle force measurement can be a useful assessment tool for clinicians.