Cross-cultural adaptation and validation of the Portuguese version of the Knee injury and Osteoarthritis Outcome Score (KOOS)

Summary Objective The objective of this study was to translate and culturally adapt the Knee injury and Osteoarthritis Outcome Score (KOOS) to the Portuguese language and to test its reliability, validity, floor/ceiling effects and responsiveness. Methods This new version was obtained with forward/backward translations, consensus panels and a pre-test. The Portuguese KOOS and Medical Outcomes Study - 36 item Short Form (SF-36) questionnaires, visual analogue scales (VAS) of pain, disability and discomfort, and a form for the characteristics of the patients were applied to 223 subjects with knee osteoarthritis (OA). Results Reliability was acceptable with Cronbach's alpha coefficients between 0.77 and 0.95, and intraclass correlation coefficients (ICC) ranging from 0.82 to 0.94 for the KOOS subscales. Construct validity was supported by the confirmation of six of the seven predefined hypotheses involving expected correlations between KOOS subscales, SF-36 subscales and VAS. An additional predefined hypothesis was also confirmed with the subjects that need walking aids obtaining lower scores in all five KOOS subscales ( P ≤ 0.001). Floor/ceiling effects were considered to be not present, except for the subscale function in sport and recreation (33.6% of the subjects reported worst possible score). Responsiveness to 4 weeks of physical therapy was demonstrated with standardized effect size between 0.78 and 1.08, and standardized response mean ranging from 0.83 to 1.37 for the KOOS subscales. Conclusion The Portuguese KOOS evidenced acceptable psychometric characteristics.