Measurement properties of the short version of the Western Ontario and McMaster Universities Arthritis Index (WOMAC) for individuals with knee osteoarthritis

BACKGROUND: Assessment instruments play an essential role in the management of knee osteoarthritis. This study aimed to verify the clinimetric properties and validate the short version of WOMAC’s (SV-WOMAC) knee with two domains, pain (four items) and physical function (eight items) in individuals with knee osteoarthritis (KO). METHODS: Reliability and internal consistency Construct, criterion validity, Ceiling, and floor effects analyses were performed. In addition to the SV-WOMAC, the following instruments were used: the numerical rating scale (NRPS), International Knee Documentation Committee (IKDC), the Short Form Health Survey (SF-36), and WOMAC’s original version. Spearman’s correlation coefficient (rho) was used to determine the magnitude of the correlation between the AFAQ and the other instruments. Moreover, the test–retest reliability and internal consistency were assessed using the intraclass correlation coefficient (ICC) and Cronbach’s alpha, respectively. In addition, standard error of measurement (SEM) and minimum detectable change (MDC) were calculated. RESULTS: One hundred and thirteen subjects with KO were included for validity analysis, and a subsample of 53 subjects was used for test-retest reliability. Adequate reliability and internal consistency were observed with ICC ≥ 0.76, SEM ≤ 1.85, MDC ≥ 5.1, and Cronbach’s alpha ≥ 0.84. Regarding construct validity, correlations greater than 0.50 were observed with the IKDC, NRPS, and functional domains of the SF-36. The SV-WOMAC showed a correlation > 0.70 with the original version and did not show ceiling and floor effects. CONCLUSION: The SV-WOMAC knee has adequate measurement properties to analyze pain and physical function in Brazilian individuals with KO.