Reliability and Validity of the Osteoarthritis Research Society International Minimal Core Set of Recommended Performance-Based Tests of Physical Function in Knee Osteoarthritis in Community-Dwelling Adults

Background: The proper reliability analysis for specific type of data and limit study of various types of construct validity are crucial for performance-based tests for the knee osteoarthritis (OA) population. The purpose of this study was to evaluate relative and absolute reliability and construct validity of the Osteoarthritis Research Society International (OARSI) recommended minimal core set of performance-based tests in knee OA in community-dwelling adults. Methods: Fifty-five primary knee OA (median age 69.0, interquartile range [IQR] 11.0) participated in the cross-sectional study. Three performance-based tests were performed in two sessions with a 1-week interval; 30-s chair stand test, 40-m fast-paced walk test and 9-step stair climb test. Relative reliability included intra-class correlation and Spearman's correlation coefficient (SPC). Absolute reliability included standard error of measurement, minimum detectable change, coefficient of variance, limit of agreement (IAA) and ratio LOA. Knee Injury and Osteoarthritis Outcome Score-Physical Function Short Form (KOOS-PS), knee extensor strength and pain scale were analysed for convergent validity using Pearson's correlation coefficient and SPC. Analysis of Covariance was utilised for known-groups validity. Results: Relative and absolute reliability were all acceptable. LOA showed small systematic bias. Acceptable construct validity was only found with knee extensor strength. All tests demonstrated known-groups validity with medium to large effect size. Conclusion: The OARSI minimum core set of performance-based tests demonstrated acceptable relative and absolute reliability and good known-groups validity but poor convergent validity.