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?

Purpose: 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.

Methods: 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.

Results: 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).

Conclusions: 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.

Level Of Evidence: Validating cohort study, Level 1b.