Validation of the Polish version of the Knee injury and Osteoarthritis Outcome Score (KOOS) in patients with osteoarthritis undergoing total knee replacement.

OBJECTIVE: To test the clinimetric properties and to evaluate the internal consistency, validity and reliability of the Polish version of the Knee injury and Osteoarthritis Outcome Score (KOOS) in older patients with end-stage knee osteoarthritis undergoing total knee replacement (TKR).

DESIGN AND SETTING: A prospective cohort study performed at the university hospital and the outpatient clinic.

METHODS: The patients were asked to complete the KOOS questionnaire and the Short Form 36 Health Survey. We evaluated floor/ceiling effects, reliability (using Cronbach's α, intraclass correlation coefficients (ICC) and measurement error), structural validity (performing exploratory principal factor analysis), construct validity (with the use of 3 a priori hypotheses) and responsiveness (using data obtained before and after the surgery, and described by Global Perceived Effect, effect size and standardised response mean).

RESULTS: The study consisted of 68 participants (mean age 68.8, 82% women). The floor effects were found prior to surgery for the subscales Sports and Recreation Function, and Quality of Life. The Cronbach's α was from 0.90 to 0.92 for all subscales, indicating excellent internal consistency. The test-retest reliability at follow-up was excellent, with ICCs ranging from 0.81 to 0.86 for all KOOS subscales. The minimal detectable change ranged from 18.2 to 24.3 on an individual level and from 2.4 to 2.9 on a group level. All KOOS items were relevant, and all a priori established hypotheses were supported. Responsiveness was confirmed with a statistically significant correlation between all KOOS subscales and the Global Perceived Effect score (ranging from 0.56 to 0.70, p<0.001).

CONCLUSIONS: The Polish version of KOOS demonstrated good reliability, validity and responsiveness for use in patient groups that had undergone TKR. Since the smallest change considered clinically relevant cannot reliably be detected in individual cases, the Polish version of KOOS is advocated for assessment of groups of patients.