Patient acceptable symptom state for New Knee Society Score after primary total knee arthroplasty

Patient-reported outcome measures (PROMs) play a crucial role in evaluating surgical success by incorporating patient perspectives in total knee arthroplasty (TKA). While the Patient Acceptable Symptom State (PASS) has been established for various PROMs, its threshold for the new Knee Society Score (2011KSS) remains undetermined. This study aimed to determine PASS thresholds for the 2011KSS.

A retrospective study was conducted on patients with knee osteoarthritis who underwent TKA and voluntarily completed satisfaction questionnaires and the 2011KSS at one or two years postoperatively. Patients were included regardless of age sex, severity of osteoarthritis, degree of deformity, or implant type. The 2011KSS Symptoms, Satisfaction, and Functional Activities domains were analyzed. PASS was evaluated based on a single question asking whether patients were satisfied or unsatisfied with the postoperative condition. PASS thresholds were determined using receiver operating characteristic (ROC) curve analysis with area under the curve (AUC). The Youden index identified optimal cutoff values.

A total of 135 and 87 patients were included in the one- and two-year analyses, respectively. ROC analysis demonstrated significant discriminatory ability, with AUC values of 0.73 (95 % confidence interval: 0.60 to 0.87), 0.76 (0.63-0.88), and 0.77 (0.67-0.88) for the one-year, and 0.97 (0.94-1.00), 0.91 (0.83-0.98), and 0.75 (0.59-0.90) for the two-year 2011KSS Symptoms, Satisfaction, and Functional Activities domains. The PASS thresholds for 2011KSS Symptoms, Satisfaction, and Functional Activities were 17, 22, and 49 at one year, and 21, 30, and 55 at two years, respectively.

This study established clinically meaningful PASS thresholds for the 2011KSS at one and two years post-TKA. These thresholds enhance the applicability of the 2011KSS by providing benchmarks for patient satisfaction, supporting clinical decision-making, and facilitating outcome comparisons in research and clinical practice.