Defining MCID, SCB, and PASS for Kujala and HSS Patella Scores After Total Knee Arthroplasty.

Purpose

Anterior knee pain remains a common cause of dissatisfaction after total knee arthroplasty (TKA). Although patient-reported outcome measures are widely used, clinically meaningful thresholds for patellofemoral-specific scores are not well established. This study aimed to determine the minimal clinically important difference (MCID), substantial clinical benefit(SCB), and patient acceptable symptom state (PASS) for the Kujala and HSS patella scores following TKA.

Methods

A retrospective cohort study included 205 patients who underwent primary TKA with a minimum follow-up of two years. Outcomes were assessed using Kujala and HSS Patella scores pre- and postoperatively. The Global Rating of Change (GRC) scale was used as an anchor. MCID was defined by comparing patients reporting "slightly better" (GRC=4) with those reporting no change or worsening (GRC ≤ 3), excluding GRC = 5. SCB was defined as GRC=5. PASS was determined based on patient satisfaction. Receiver operating characteristic (ROC) curve analysis with the Youden index identified optimal thresholds.

Results

MCID values were 15.5 for the Kujala score and 21.5 for the HSS score. SCB thresholds were 21.5 and 30.5, respectively. PASS thresholds were 78.5 for Kujala and 70.5 for HSS. Both scores showed acceptable discrimination for MCID (AUC ≈ 0.72) and excellent performance for SCB and PASS (AUC > 0.85). Significant correlations were found between GRC and score changes (p < 0.001).

Conclusion

Clinically meaningful thresholds for Kujala and HSS Patella scores were established in TKA patients. These values may improve interpretation of outcomes and support patient-centered assessment in clinical practice and research.