Objective: To test the reliability, validity and responsiveness of the Portuguese version of the Knee injury and Osteoarthritis Outcome Score--Physical Function Short-form (KOOS-PS).
Methods: The Portuguese full KOOS and Medical Outcomes Study e 36 item Short-Form (SF-36) questionnaires, and a form of individual characteristics of the patients were applied to 85 subjects with knee osteoarthritis (OA).
Results: Cronbach's alpha coefficient was 0.89 and intraclass correlation coefficient (ICC) was 0.85, certifying that KOOS-PS reliability was acceptable. Construct validity was supported by the confirmation of the five predefined hypotheses involving expected correlations between KOOS-PS scale, KOOS subscales and SF-36 subscales. An additional predefined hypothesis was also confirmed with the subjects that need walking aids obtaining higher KOOS-PS scale scores (P = 0.011). Responsiveness to 4 weeks of conventional physical therapy treatments and to a 6-week health education and exercise program was demonstrated with a standardized effect size of 0.88 and 0.50, and a standardized response mean of 1.21 and 0.73, respectively.
Conclusion: The Portuguese KOOS-PS evidenced acceptable psychometric characteristics.