Responsiveness and minimal clinically important changes of common patient-reported and performance-based outcome measures of physical function in patients with knee osteoarthritis.

Purpose: We investigate and compare responsiveness of the physical function subscales of patient-reported measures of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Oxford Knee Score (OKS), and performance-based measures of the timed up-and-go test and 6-min walk test and determine the minimal clinically important change (MCIC) values in knee osteoarthritis (OA) patients following physiotherapy intervention.

Methods: One hundred patients were asked to complete the WOMAC and OKS and to perform the timed up-and-go test and 6-min walk test once pre-intervention and again after 4-week physiotherapy intervention (post-intervention). Responsiveness was determined by correlation analysis and receiver operating characteristics (ROC) curve.

Results: The WOMAC-physical function subscale (WOMAC-PF), OKS-functional component score (OKS-FCS), timed up-and-go test, and 6-min walk test showed moderate-to-good relationships with the patients' global rating scale (Spearman correlation ranges = 0.51-0.56). All outcome measures of physical function showed the area under the curve (AUC) >0.70 (AUC ranges = 0.78-0.82). The MCIC values were 12.5 points for WOMAC-PF, 17.5 points for OKS-FCS, 2.82 s for timed up-and-go test, 61 m for 6-min walk test.

Conclusions: All outcome measures have adequate responsiveness to detect clinical improvements over time in functional status following the physiotherapy intervention in patients with knee OA. The MCIC values can help clinicians and researchers to make a decision based on the clinical significance of improvements in patients' functional status.