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.