Validation of the German Forgotten Joint Score (G-FJS) according to the COSMIN checklist: does a reduction in joint awareness indicate clinical improvement after arthroplasty of the knee?

Evaluation of further improvement in treatment of patients with osteoarthritis of the knee requires measurement tools with a high discriminatory power. In this context, joint awareness in everyday life is seen as crucial criterion. Purpose of this study was to adapt and validate a German version of the "Forgotten Joint Score" (FJS) according to the COSMIN checklist. We evaluated a German translation of the FJS for reliability, validity and responsiveness according to the COSMIN checklist. Therefore, patients with an artificial knee joint completed the G-FJS questionnaire twice at intervals of at least 2 weeks. In addition, the Knee Society Score, the Oxford Knee Score, the Tegner Activity Scale, a Visual Analogue Scale, the EuroQol-5D (EQ 5-D), and a subjective assessment of the limitations were recorded. Between June and December 2014, one hundred and five patients (average age 65.2 years) completed both questionnaires and were available for data analysis. Test-retest reliability of the FJS was high with an ICC = 0.80 (95 % CI 0.69, 0.90) and with a Cronbach's alpha of 0.95 (95 % CI 0.92, 0.99). The German translation of the FJS is a viable tool for the postoperative monitoring after arthroplasty of the knee. This is the first study providing data on test-retest reliability of the FJS. The FJS is a reliable and valid measurement tool for evaluation of patient rated outcome in patients with an artificial knee joint. Validating cohort study, Level 1b