The test-retest reliability of a new measurement of lower extremity isometric muscle strength for patients with knee osteoarthritis

Objective To determine the test-retest reliability of functional squat system (FSS) isometric muscle strength tests for patients with knee osteoarthritis. Methods The isometric muscle strength of thirty patientswith knee osteoarthritis (21 males and 9 females; age 45 to 89 years, mean age 68.73 ± 12.19 years) was tested twice within 1 week by the same tester. Three test results were obtained: maximum isometric extension strength, the time to initiate isometric extension and the average isometric extension strength. Intra-class correlation coefficients (ICCs) for the three tests were computed to evaluate their retest reliability. Results The ICCs of the maximum isometric extension strength and average isometric extension strength of the uninvolved and involved extremities were respectively 0.87, 0.88, 0.92 and 0.89. The ICCs of the initiation time for the uninvolved and involved legs were respectively 0.25 and 0.41. Conclusion In these tests of patients with knee osteoarthritis using the functional squat system, both the maximum isometric extension strength and the average isometric extension strength had very good test-retest reliability. These two test results could be used as reliable guidance for treatment and rehabilitation of osteoarthritic knees. Key words: Knee osteoarthritis;  Isometric muscle strength;  Tests;  Retest reliability