BACKGROUND:
The original structure of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) has been contested in several languages.
OBJECTIVE:
To assess the structural validity of the Brazilian version of WOMAC among patients with knee osteoarthritis.
DESIGN AND SETTING:
Structural validity study conducted at physiotherapy clinics and primary healthcare units.
METHODS:
The study included males and females aged 40 to 80 years who were all native Brazilian Portuguese speakers, with knee pain in the previous six months and a diagnosis of knee osteoarthritis. We used exploratory factor analysis (EFA) followed by confirmatory factor analysis (CFA) with implementation of a polychoric matrix and the robust diagonally weighted least squares (RDWLS) extraction method. The adequacy of the model was assessed using the following fit indices: root mean square error of approximation (RMSEA), comparative fit index (CFI), Tucker-Lewis index (TLI), standardized root mean square residual (SRMR) and chi-square/degree of freedom (DF).
RESULTS:
203 patients with knee osteoarthritis were included. The model proposed in this study with two factors, i.e. “pain” (items 1, 2, 3 and 4) and “physical function” (items 10, 11, 16, 17, 18, 19, 21 and 22), showed adequate fit indices in CFA: chi-square/DF = 1.30; CFI = 0.976; TLI = 0.970; RMSEA = 0.039; and SRMR = 0.070. The factorial loads ranged from 0.68 to 0.76 for the “pain” domain and 0.44 to 0.62 for the “physical function” domain.
CONCLUSION:
The Brazilian version of WOMAC with two domains, i.e. “pain” (four items) and “physical function” (eight items), presents the best structure.
KEY WORDS (MeSH terms):
Reproducibility of results; Surveys and questionnaires; Pain; Rheumatology
AUTHORS' KEY WORDS:
Joint degeneration; Exploratory factor analysis; Confirmatory factor analysis; WOMAC
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