Translation, Cross-Cultural Adaptation, and Validation of the Measure of Intermittent and Constant Osteoarthritis Pain (ICOAP) Measure into Brazilian Portuguese for Individuals with Knee Osteoarthritis

<b>Background:</b> A comprehensive understanding of chronic pain is crucial for assessing its impact on knee osteoarthritis (KOA). This study aimed to translate, cross-culturally adapt, and validate the ICOAP into Brazilian Portuguese for individuals with KOA. <b>Methods:</b> A total of 133 individuals with KOA participated. Phase 1 involved the translation and cross-cultural adaptation of the ICOAP into Brazilian Portuguese. In Phase 2, the pre-final version was tested, and in Phase 3, the final version was validated with 103 participants. Convergent validity was assessed using Spearman's correlation with the Numeric Rating Pain Scale (NRPS), the International Knee Documentation Committee (IKDC), and the Short Form 36 Health Survey (SF-36). Internal structure was evaluated through exploratory and confirmatory factor analyses using fit indices: chi-square/degrees of freedom (χ²/df), root mean square error of approximation (RMSEA), standardized root mean square residual (SRMR), comparative fit index (CFI), and Tucker-Lewis index (TLI). Internal consistency was assessed with Cronbach's alpha (α), and floor and ceiling effects were examined. A subsample of 53 participants was used to assess test-retest reliability through the intraclass correlation coefficient (ICC), standard error of measurement (SEM), and minimum detectable change (MDC). <b>Results:</b> The ICOAP showed adequate fit indices. Reliability analysis demonstrated satisfactory internal consistency and test-retest reliability. However, only the constant pain domain exhibited convergent validity. <b>Conclusions:</b> The Brazilian Portuguese version of the ICOAP consists of two independent domains with good internal consistency and reliability. However, only the constant pain domain showed appropriate convergent validity.