RESUMO
The aim of this study is to assess the reliability and validity of the Western Ontario and McMaster University Osteoarthritis Index (WOMAC) in Moroccan patients with knee osteoarthritis. The WOMAC was translated and back translated to and from dialectal Arabic, pre-tested and reviewed by a committee following the Guillemin criteria. The Moroccan version of the WOMAC was administered twice during a 24-48 h interval to 71 Moroccan patients with symptomatic knee osteoarthritis, fulfilling the revised criteria of the American College of Rheumatology. The test-retest reliability was assessed using intra-class correlation coefficient, and the Bland and Altman method. Internal consistency was assessed by Cronbach's alpha coefficient. Construct validity was tested by correlating the WOMAC subscales with visual analogic scale (VAS) of pain, VAS of handicap, maximum distance walked and clinical characteristics. The Moroccan version of the WOMAC showed good reliability, with ICC values of the three dimensions: pain, stiffness and physical function being 0.80, 0.77 and 0.89, respectively. Bland and Altman analysis showed that means of differences did not differ significantly from 0 and that no systematic trend was observed. Internal consistency with Cronbach's alpha for pain was found to be 0.76, and its equivalents for stiffness and physical function subscales were evaluated at 0.76, 0.90, respectively. Construct validity showed statistically significant correlation with all WOMAC subscales and VAS of pain (rho=0.38, 0.42, 0.63 respectively, P<0.01). Correlation between VAS handicap (rho=0.38 P<0.001) and maximum distance walked (rho=-0.40, P<0.01) was observed with physical function subscale. There was no correlation between age, duration of disease, BMI and severity of pain and physical function in knee OA. The Moroccan version of the WOMAC is a comprehensible, reliable, and valid instrument to measure outcome in patients with knee OA.