Validation of an 18-item version of the Swedish Knee Self-Efficacy Scale for patients after ACL injury and ACL reconstruction.

PURPOSE To evaluate the measurement properties of a new version of the Swedish Knee Self-Efficacy Scale (K-SES) in samples of individuals with an anterior cruciate ligament (ACL) injury and after ACL reconstruction. A secondary aim was to translate the new version of K-SES into English in order to prepare for future complete cross-cultural adaptation. METHODS The reliability, structural validity, internal consistency and construct validity of the new, 18-item version of the K-SES (K-SES18) were assessed according to the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) checklist for evaluating methodological quality. The Swedish version of the K-SES18 was translated to English using recommended guidelines. RESULTS The test-retest reliability for the K-SES18 subscale present and the K-SES18 subscale future showed an Interclass Correlation Coefficient (ICC) = 0.92. In addition, the K-SES18 had a Cronbach's α ranging from 0.93 to 0.96 for the K-SES18 subscale present and from 0.81 to 0.91 for the K-SES18 subscale future. No floor and ceiling effects were identified for the subscale present or the subscale future of the K-SES18. A factor analysis produced 2 factors of importance; K-SES18present and K-SES18future. Seven predefined hypotheses were confirmed. CONCLUSION The K-SES18 has acceptable reliability and validity to assess knee self-efficacy in patients up to 18 months after ACL injury and reconstruction. LEVEL OF EVIDENCE IV.