WOMAC Osteoarthritis Index - Reliability, validity, and responsiveness in patients with arthroscopically assessed osteoarthritis

Objective: To validate the WOMAC Osteoarthritis Index for use in Sweden. Methods: Test-retest reliability, internal consistency, validity, and respo nsiveness was determined in 52 patients (mean age 48 (20- 69)) with arthros copically assessed cartilage damage of the tibio-femoral knee joint. Results: All WOMAC scales were internally consistent with Cronbach's alpha coefficients of 0.83, 0.87, and 0.96 pre-operatively. Test-retest reliabili ty was satisfactory with intraclass correlation coefficients of 0.74, 0.58, and 0.92. As hypothesized worse post-operative but not preoperative outcom es were associated with radiographic OA. In comparison with the SF-36 the e xpected correlations were found when comparing items measuring similar and dissimilar constructs, supporting the concepts of convergent and divergent construct validity. Three months after arthroscopy significant mean improve ment was seen in all WOMAC scales (p<0.0004). Conclusion: The Swedish version of WOMAC is a reliable, valid, and responsi ve instrument with metric properties in agreement with the original widely used version.