Responsiveness of four patient-reported outcome measures to assess physical function in patients with knee osteoarthritis

Objectives: The aim of this study was to evaluate the responsiveness of four patient-reported outcome measures (PROMs) to measure change in physical function simultaneously in patients with knee osteoarthritis (OA) following currently recommended COSMIN (COnsensus-based Standards for the selection of health status Measurement INstruments) standards. Method: Patients with knee OA receiving conservative treatment following a stepped care approach were invited to complete a set of questionnaires at baseline and 3 months. Questionnaires included four widely used measures of physical function: the Knee Injury and Osteoarthritis Outcome Score Physical Function Short Form (KOOS-PS), the Lequesne algofunctional index (LAI), the Lower Extremity Functional Scale (LEFS), and the Western Ontario and McMaster University Osteoarthritis Index Physical Function subscale (WOMAC-PF). Responsiveness of physical function was investigated according to the COSMIN standards by testing 15 a priori defined hypotheses. Responsiveness was considered positive if > 75% of the hypotheses could be confirmed. Results: A total of 161 patients participated [61% female, mean (sd) age 59 (9) years and body mass index 29.7 (5.0) kg/m(2)]. Baseline values of the four PROMs were, mean (sd): KOOS-PS 53.6 (16.8), LAI 11.0 (4.0), LEFS 40.6 (14.1), and WOMAC-PF 51.8 (19.4). We could confirm 12 out of 15 predefined hypotheses (80%) about expected correlations for the WOMAC-PF whereas for the KOOS-PS, LAI, and LEFS < 75% hypotheses could be confirmed (73, 67, and 73%. respectively). Conclusions: Our results suggest that the WOMAC-PF is able to detect changes over time in physical function and therefore should be the measure of first choice in clinical trials evaluating the effectiveness of an intervention on physical function in knee OA patients.