Translation, cross-cultural adaptation, and validation of the Italian language Forgotten Joint Score-12 (FJS-12) as an outcome measure for total knee arthroplasty in an Italian population

Background: With ever-increasing numbers of patients undergoing elective total knee arthroplasty (TKA) and as TKA is performed in increasingly younger patients, patient demands and expectations have also increased. With improved patient outcomes, new PROMs with heightened discriminatory power in well-performing patients are needed. The present study aimed to translate and validate the Italian version of the Forgotten Joint Score (FJS-12) as a tool for evaluating pre-operative through longitudinal post-operative outcomes in an Italian population. Methods: In this prospective study, patients with unilateral osteoarthritis, undergoing TKA surgery between May 2015 and December 2017 were recruited to participate in the study. The FJS-12 and WOMAC were collected pre-operatively and at six and 12 months post-operatively. According to the COSMIN checklist, reliability, internal consistency, validity, responsiveness, effect size, and ceiling effects and floor effects were evaluated. Results: One hundred twenty patients completed the study, 66 of which participated in the evaluation of test-retest reliability. Good test-retest reliability was found (ICC = 0.90). The FJS-12 also showed excellent internal consistency (Cronbach α = 0.81). Construct validity with the WOMAC, as a measure of the Pearson correlation coefficient, was moderate (r = 0.45 pre-operatively; r = 0.46 at 6 months and r = 0.42 at 12 months post-operatively). From six to 12 months, the change was slightly greater for the WOMAC than for the FJS-12 patients (effect size d = 0.94; d = 0.75, respectively). At 12-months follow-up, the ceiling effects reflecting the maximum score were 12% for the FJS-12 and 6% for the WOMAC; however, scores within 10% of the maximum score were comprised 30% of the FJS-12 scores and 59% for the WOMAC. Conclusion: The Italian FJS-12 demonstrated strong measurement properties in terms of reliability, internal consistency, and construct validity in TKA patients. Furthermore, a more detailed look at ceiling effects shows a superior discriminatory capacity when compared to the WOMAC at 12-months follow-up, particularly in better-performing patients. Trial registration: clinicaltrials.gov NCT03805490. Registered 18 January 2019 (retrospectively registered).