Test-retest reliability of the peak knee adduction moment during walking in patients with medial compartment knee Osteoarthritis

Objective. To estimate the test-retest reliability of the peak external knee adduction moment during walking in patients with medial compartment knee osteoarthritis (OA), and to describe the interpretation of the reported values. Methods. A total of 31 patients diagnosed with knee OA confined primarily to the medial compartment underwent quantitative gait analyses during 2 separate test sessions at least 24 hours apart and within 1 week. The peak knee adduction moment was calculated for each patient at each session based on the mean of 5 walking trials. Reliability was estimated using the intraclass correlation coefficient (ICC2,1) and the standard error of measurement (SEM). Results. The mean difference in peak adduction moments between test sessions was 0.1% body weight x height (BW x ht; 95% confidence interval [95% CI] -0.1, 0.3). The point estimate for the ICC was 0.86 (95% CI 0.73, 0.96). The point estimate for the SEM was 0.36% BW x ht (95% CI 0.29, 0.48). Conclusion. The ICC suggests that the peak knee adduction moment is appropriate for use when distinguishing among patients, for example, in studies of various interventions intended to decrease dynamic load on the knee medial compartment. The SEM illustrates the importance of considering measurement error and incorporating confidence levels when interpreting an individual patient's peak knee adduction moment value.