Development of the Italian version of the knee injury and osteoarthritis outcome score for patients with knee injuries: Cross-cultural adaptation, dimensionality, reliability, and validity

Objective: Translating, culturally adapting and validating an Italian version of the Knee injury and Osteoarthritis Outcome Score (KOOS-I) to allow its use with Italian-speaking patients with knee complaints. Design: The KOOS-I was developed by means of forward-backward translation, a final review by an expert committee, and a test of the pre-final version to establish its correspondence with the original English version. The psychometric testing included analysis of dimensionality using item-scale correlation after correction for overlap, reliability by means of internal consistency (Cronbach's alpha) and test-retest reliability (Intraclass Correlation Coefficients), and construct validity using an a priori hypothesised Pearson correlations with a Numerical Rating Scale (NRS) and the Short-Form 36 Health Survey (SF-36). Results: The questionnaire was administered to 224 subjects with knee injuries and proved to be acceptable. Hypothesised item-to-domain correlations were observed for all of the items. The questionnaire showed good internal consistency (0.782-0.977), and a high level of test-retest reliability (0.850-0.949). Construct validity was supported by the confirmation of the a priori hypothesised correlations. Conclusions: The KOOS outcome measure was successfully translated into Italian, and proved to have good psychometric properties that replicated the results of existing versions. Its use is recommended for clinical and research purposes in patients with knee injuries.