The Forgotten Joint Score Is a Valid Outcome Measure for Total Ankle Arthroplasty: A Prospective Study

The success of total ankle arthroplasty (TAA) involves objective and subjective parameters such as joint motion and implant survival. Patient-reported outcome measures provide key context from the patient's perspective so that we can evaluate the results of these procedures. The Forgotten Joint Score (FJS) has demonstrated validity and reliability in other arthroplasties, but the existing evidence on the FJS in TAA is very limited.

We aimed to assess the reliability, validity, responsiveness to change, and floor and ceiling effects, as well as to perform a gender analysis, of the FJS in patients who had undergone TAA.

A prospective, observational study enrolled patients who underwent TAA at our institution between June 2021 and May 2023. The three-component TAA was performed through an anterior approach. A total of 120 patients (mean age 62 ± 10 years) participated, which was 83% (120 of 145) of those eligible, and 77% (92 of 120) of those patients underwent follow-up assessments at 12 ± 1 months after surgery. A cross-culturally adapted and validated version of the FJS in our language (Italian) was used. Additionally, three other commonly used patient-reported outcome measures for TAA were administered: the American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score, the Manchester-Oxford Foot Questionnaire (MOXFQ), and the VAS.

Reliability was demonstrated by excellent internal consistency (Cronbach α coefficient = 0.95) and excellent test-retest reliability (intraclass correlation coefficient = 0.99; standard error of measurement = 2.7). Robust validity was observed, in that the FJS had a strong correlation with the AOFAS ankle-hindfoot score, the MOXFQ, and the VAS (Pearson and Spearman values consistently above 0.7 or below -0.7). Responsiveness to change was observed between 6 and 12 months (Cohen d = 0.37). Low ceiling and floor effects at both 6 months (4% and 3% reached top and bottom scores, respectively) and 12 months (10% and 0% reached top and bottom scores, respectively) were demonstrated, below the recommended 15% interpretability threshold. No association between outcomes and patient gender was observed.

Test properties and validity of the FJS were strong in patients who underwent TAA. It seems suitable for clinical use, although future studies should seek to replicate or refute our findings in other patient populations.

Level II, therapeutic study.