Objective: To assess and compare the test-retest reliability and the construct validity of the Lequesne and the French-Canadian version of the WOMAC indexes.
Design: Patients with symptomatic knee osteoarthritis (OA) fulfilling the revised criteria of the American College of Rheumatology completed both the Lequesne and the French-Canadian version of the WOMAC indexes twice at a 3-h interval. Impairment outcome measures, patients' perceived discomfort in walking and handicap were recorded. For both questionnaires, an analysis was performed item by item. Repeatability was assessed using the intraclass correlation coefficient (ICC) and the Bland and Altman method. Construct validity was investigated using the Spearman rank correlation coefficient and a factor analysis was performed.
Results: 88 patients were included. Eight questions of the WOMAC section C and one question of the Lequesne index had insufficient psychometric properties. Although repeatability of questionnaires was fair to excellent (0.82, 0.68, 0.74, 0.95 for the WOMAC sections A, B, C and Lequesne index respectively), construct validity could not be demonstrated. Factor analysis of the WOMAC extracted five factors which differed from the a priori triple stratification. Factor analysis of the WOMAC section C extracted two factors explaining 71% of the variance which could not be clinically characterized. For the Lequesne index, expected convergent correlations were not always achieved. Three factors were extracted by factor analysis explaining 58% of the variance.
Conclusion: Despite their good test-retest reliability, the two composite indexes evaluated are not valid to assess the concept of functional disability induced by knee OA in a French population.