Assessment of the test-retest reliability and construct validity of a modified Lequesne index in knee osteoarthritis

OBJECTIVES: To assess the test-retest reliability and the construct validity of a modified version of the Lequesne index. METHODS: Patients with symptomatic knee osteoarthritis (OA) fulfilling the revised criteria of the American College of Rheumatology completed the Lequesne index twice at a 3-h interval. Impairment outcome measures and patients' perceived discomfort in walking and handicap were recorded. An item-by-item analysis was performed. Items having insufficient psychometric properties were excluded. Test-retest reliability was assessed using the intra-class correlation coefficient (ICC) and the Bland and Altman method. Construct validity was investigated using Spearman rank correlation coefficient and a factor analysis was performed. RESULTS: Eighty-eight patients were included. One question assessing pain (question IE) had a weak reliability (Kappa (kappa) = 0.39) and was excluded. The test-retest reliability of the modified questionnaire was excellent (ICC = 0.95). Expected convergent and divergent correlations were achieved except for visual analog scale pain (VAS P) and VAS handicap (VAS H) (0.46 and 0.40, respectively), and the "a priori" double stratification was confirmed by factor analysis, explaining 48.7% of the variance. CONCLUSION: The modified form of the Lequesne index has sufficient psychometric properties to be used to assess pain and function in knee OA in a French population.