Background: In order to better understand the clinical benefits of total knee arthroplasty (TKA) and improve the interpretability of the Forgotten Joint Score (FJS-12), the establishment of a meaningful change in score is necessary. The purpose of this study is to determine the threshold of the FJS-12 for detecting the patient acceptable symptom state (PASS) following primary TKA.
Methods: We retrospectively reviewed all patients who underwent elective, primary TKA and answered both the FJS-12 and the Knee Injury Osteoarthritis Outcome Survey, Joint Replacement KOOS, JR surveys 1-year postoperatively. The questionnaires were administered via a web-based electronic application. KOOS, JR score was used as the anchor. The anchor for PASS calculation should relate pain, physical function, and patient satisfaction. Two statistical methods were employed: (1) the receiver operating characteristic (ROC) curve point; (2) 75th percentile of the cumulative percentage curve of patients who had the KOOS, JR score difference larger than the cut-off value.
Results: This study included 457 patients. The mean 1-year FJS-12 score was 42.6 ± 27.8. The mean 1-year KOOS, JR score was 68.0 ± 17.2. A high positive correlation between FJS-12 and KOOS, JR was found (r = 0.72, P < .001) making the KOOS, JR a valid external anchor. The threshold score of the FJS-12 which maximized the sensitivity and specificity for detecting a PASS was 33.3 (AUC = 0.78, 95% CI [0.74, 0.83]). The cut-off value computed with the 75th percentile approach was 77.1 (95% CI [73.9, 81.5]).
Conclusion: The PASS threshold for the FJS-12 was 33.3 and 77.1 at 1-year follow-up after primary TKA using the receiver operating characteristic (ROC) curve and 75th percentile approaches, respectively. These values can be used to assess the successful achievement of a forgotten joint.
Level iii evidence: Retrospective Cohort Study.
Keywords: MCID; forgotten joint score; knee replacement; minimal clinically important difference; patient acceptable symptom state; total knee arthroplasty.
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