Translation, cross-cultural adaptation, reliability, validity, and responsiveness of the Brazilian Portuguese version of the Knee Injury and Osteoarthritis Outcome Score for Children (KOOS-Child) in children and adolescents with knee injuries

To translate, culturally adapt, and evaluate the reliability, validity, and responsiveness of the Brazilian Portuguese version of the Knee Injury and Osteoarthritis Outcome Score for Children (KOOS-Child-Br) in children and adolescents with knee injuries. This is a clinical measurement study. Cross-cultural adaptation was assessed via cognitive debriefing. Test–retest reliability was evaluated using the intraclass correlation coefficient (ICC2,1). Internal consistency was assessed using Cronbach’s alpha. Construct validity was assessed by correlations between KOOS-Child-Br subscales and the Pediatric Quality of Life Inventory (PedsQL™), and between the pain subscale and the Numerical Pain Rating Scale (NPRS). Responsiveness was evaluated through correlations with the Global Perceived Effect Scale (GPES) and effect size. 135 participants were evaluated. KOOS-Child-Br subscales showed excellent test-retest reliability (ICC2,1 = 0.84–0.91) and adequate internal consistency (α = 0.77–0.93). KOOS-Child-Br showed moderate to good correlation with the PedsQL™ (r = 0.65–0.82), moderate correlation between the pain subscale and the NPRS (r = −0.66), moderate to high effect size (0.60–0.84) and an adequate correlation with the GPES (rho = 0.35–0.56). KOOS-Child-Br is reliable, valid and responsive in children and adolescents with knee injuries. Knee Injury and Osteoarthritis Outcome Score for Children (KOOS-Child-Br) is the first questionnaire in Brazilian Portuguese to assess children and adolescents with knee injuries.KOOS-Child-Br demonstrated adequate levels of reliability and internal consistency.KOOS-Child-Br showed good validity and responsiveness.The results support the use of the Brazilian Portuguese version of the KOOS-Child in both clinical practice and research. Knee Injury and Osteoarthritis Outcome Score for Children (KOOS-Child-Br) is the first questionnaire in Brazilian Portuguese to assess children and adolescents with knee injuries. KOOS-Child-Br demonstrated adequate levels of reliability and internal consistency. KOOS-Child-Br showed good validity and responsiveness. The results support the use of the Brazilian Portuguese version of the KOOS-Child in both clinical practice and research.