Translation, cross-cultural adaptation, and clinimetric testing of instruments used to assess patients with patellofemoral pain syndrome in the Brazilian population

Clinical measurement study. To cross-culturally adapt the Anterior Knee Pain Scale (AKPS), the Functional Index Questionnaire (FIQ), and the Pain Severity Scale (PSS) for patellofemoral pain syndrome (PFPS) into Brazilian Portuguese. This study also aimed to test the measurement properties of the AKPS, the FIQ, and the PSS, and the existing Brazilian Portuguese versions of the numeric pain rating scale (NPRS) and the Global Perceived Effect scale in a group with PFPS. PFPS is a common condition. Therefore, translated, culturally adapted, and clinimetrically tested instruments for measuring PFPS are needed. The AKPS, FIQ, and PSS instruments were cross-culturally adapted into Brazilian Portuguese. The measurement properties of the AKPS, FIQ, PSS, NPRS, and Global Perceived Effect scale (internal consistency, ceiling and floor effects, and construct validity) were tested in 83 patients with PFPS. The reproducibility and responsiveness were tested in 52 patients with PFPS in a test-retest design, with follow-up testing at 48 to 72 hours and at 4 weeks after baseline. The AKPS, the FIQ, and the PSS yielded adequate internal consistency (Cronbach alpha ranging from .75 to .87) and excellent reliability (intraclass correlation coefficients [model 2,1] ranging from 0.90 to 0.97). The AKPS and the PSS yielded very good agreement (standard error of measurement, 2.9% and 3.5%, respectively). The highest correlations were observed among the AKPS, the FIQ, and the PSS (Pearson r>0.60, P