RESUMO
PURPOSE: To translate and cross-culturally adapt the Spine Functional Index (SFI) into Brazilian Portuguese (SFI-Br) in individuals with musculoskeletal spine disorders. METHODS: Participants (n=194) answered the Numerical Pain Rating Scale (NPRS), 36-item Short-Form Health Survey (SF-36), Roland-Morris Disability Questionnaire for General Pain (RMDQ-g), and SFI-25 incorporating the SFI-10. Structural validity, from confirmatory factor analysis (CFA), used comparative fit index (CFI), Tucker-Lewis index (TLI), root mean square error of approximation (RMSEA), and chi-square/degrees of freedom (DF). The best structure was considered from the lower values of the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC). Construct and criterion validity used Spearman's correlation coefficient (rho). Internal consistency used Cronbach's alpha, reliability used intraclass correlation coefficient (ICC2,1), with ceiling and floor effects determined. Error used the standard error of the measurement (SEM) and minimal detectable change, 90% level (MDC90). RESULTS: Adequate fit indices demonstrated an unequivocal one-factor structure only for the SFI-10 (chi-square/DF <3.00, CFI and TLI >0.90, RMSEA <0.08). The SFI-10-Br correlation was high with the SFI-Br (rho=0.914, p<0.001), moderate for the RMDQ-g (rho=-0.78), SF-36 functional capacity domain (rho=0.718) and NPRS (rho=-0.526); and adequate for the remaining SF-36 domains (rho>0.30). Test-retest reliability (ICC2,1=0.826) and internal consistency (alpha=0.864) were high. No ceiling or floor effects were observed, and error was satisfactory (SEM=9.08%, MDC90=25.15%). CONCLUSION: The SFI Brazilian version was successfully produced with the 10-item version showing an unequivocal one-factor structure, high construct and criterion validity, reliability, internal consistency, and satisfactory error. Further research on responsiveness is required.
