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-SES(18)) 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-SES(18) was translated to English using recommended guidelines. RESULTS: The test-retest reliability for the K-SES(18) subscale present and the K-SES(18) subscale future showed an Interclass Correlation Coefficient (ICC) = 0.92. In addition, the K-SES(18) had a Cronbach’s α ranging from 0.93 to 0.96 for the K-SES(18) subscale present and from 0.81 to 0.91 for the K-SES(18) subscale future. No floor and ceiling effects were identified for the subscale present or the subscale future of the K-SES(18). A factor analysis produced 2 factors of importance; K-SES(18)present and K-SES(18)future. Seven predefined hypotheses were confirmed. CONCLUSION: The K-SES(18) 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. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40634-021-00414-2.