Introduction: The aim of this study was to translate the Pediatric International Knee Documentation Committee Score (Pedi-IKDC) into European Portuguese language. The Pedi-IKDC was originally developed in the English language and its main construct is functional assessment of knee disorders in children and adolescents.
Material and Methods: The original English version of the questionnaire was translated to European Portuguese using the forwardbackwards method. Patients aged eight to 17 with knee disorders were considered eligible for the study. An online platform was implemented to collect patient responses, including general patient information, the questionnaires Pedi-IKDC, EuroQol-5 Dimension Youth and Childhood Health Assessment Questionnaire. Three surveys were sent: at the moment of first evaluation (T0), after two (T1) and ten (T2) weeks. These surveys followed the Consensus-based Standards for the Selection of Health Measurement Instruments - COSMIN Checklist recommendations. The internal consistency, reliability, error of measurement, structural and construct validity (by means of correlation with previously validated scales), responsiveness and interpretability (floor/ceiling effects, MIC and ROC curve) were evaluated.
Results: Forty-seven patients completed T0, 42 patients completed T1 and 40 patients completed T2. The factorial analysis confirmed that the scale has one dimension. Cronbach alpha (α) was 0.94; interclass correlation coefficient was 0.92; smallest detectable change was 19.04 for individuals and 3.31 for groups; standard error of measurement was 6.87; minimum important change was 18.48; floor and ceiling effects were absent. More than 75% of the hypotheses tested for construct validity were confirmed, showing its adequacy. The variation of scores between T0 and T2 correlated with the clinical evolution of the participants (r = 0.421, p < 0.05).
Conclusion: The Portuguese version of Pedi-IKDC demonstrated good psychometric properties, being a valuable tool for clinical assessment of pediatric patients with knee disorder.

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