Cross-cultural adaptation, reliability and validity of the Arabic version of the reduced Western Ontario and McMaster Universities Osteoarthritis index in patients with knee osteoarthritis

Purpose: We adapted the reduced Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index for the Arabic language and tested its metric properties in patients with knee osteoarthritis (OA). Methods: One hundred and twenty-one consecutive patients who were referred for physiotherapy to the outpatient department were asked to answer the Arabic version of the reduced WOMAC index (ArWOMAC). After the completion of the ArWOMAC, the intensity of knee pain and general health status were assessed using the visual analog scale (VAS) and the 12-item short form health survey (SF-12), respectively. A second assessment was performed at least 48 h after the first session to assess test-retest reliability. The test-retest reliability was quantified using the intra-class correlation coefficient (ICC), and Cronbach's alpha was calculated to assess the internal consistency of the Arabic questionnaire. The construct validity was assessed using Spearman rank correlation coefficients. Results: The total ArWOMAC scale and pain and function subscales were internally consistent with Cronbach's coefficient alpha of 0.91, 0.89 and 0.90, respectively. Test-retest reliability was good to excellent with ICC of 0.91, 0.89 and 0.90, respectively. SF-12 and VAS score significantly correlated with ArWOMAC index (p<0.01), which support the construct validity. The standard error of measurement (SEM) of the total scale was 2.94, based on repeated measurements for test-retest. The minimum detectable change based on the SEM for test-retest was 8.15. Conclusions: The ArWOMAC index is a reliable and valid instrument for evaluating the severity of knee OA, with metric properties in agreement with the original version. ▸ Implications for Rehabilitation • Although, the reduced WOMAC index has been clinically utilized within the Saudi population, the Arabic version of this instrument is not validated for an Arab population to measure lower limb functional disability caused by OA. • The Arabic version of reduced WOMAC (ArWOMAC) index is a reliable and valid scale to measure lower limb functional disability in patients with knee OA. • The ArWOMAC index could be suitable in Saudi Arabia and other Arab countries where the language, culture and the life style are similar.