Establishing the Minimal Clinically Important Difference and Patient Acceptable Symptomatic State following Patellofemoral Inlay Arthroplasty for Visual Analog Scale Pain, Western Ontario and McMaster Universities Arthritis Index, and Lysholm Scores

Background: The purposes of the study were to define the minimal clinically important difference (MCID) and patient acceptable symptomatic state (PASS) after patello-femoral inlay arthroplasty (PFA) and to identify factors predictive for the achievement of clinically important outcomes (CIOs). Methods: A total of 99 patients who underwent PFA between 2009 and 2019 and had a minimum of 2-year postoperative follow-up were enrolled in this retrospective monocentric study. Included patients had a mean age of 44 years (range, 21 to 79). The MCID and PASS were calculated using an anchor-based approach for the visual analog scale (VAS) pain, Western Ontario and McMaster Universities Arthritis Index (WOMAC), and Lysholm patient-reported outcome measures. Factors associated with CIO achievement were determined using multivariable logistic regression analyses. Results: The established MCID thresholds for clinical improvement were −2.46 for the VAS pain score, −8.5 for the WOMAC score, and + 25.4 for the Lysholm score. Postoperative scores corresponding to the PASS were <2.55 for the VAS pain score, <14.6 for the WOMAC score, and >52.5 points for the Lysholm score. Preoperative patellar instability and concomitant medial patello-femoral ligament reconstruction were independent positive predictors of reaching both MCID and PASS. Additionally, inferior baseline scores and age were predictive of achieving MCID, whereas superior baseline scores and body mass index were predictive of achieving PASS. Conclusion: This study determined the thresholds of MCID and PASS for the VAS pain, WOMAC, and Lysholm scores following PFA implantation at 2-year follow-up. The study demonstrated a predictive role of patient age, body mass index, preoperative patient-reported outcome measure scores, preoperative patellar instability, and concomitant medial patello-femoral ligament reconstruction in the achievement of CIOs. Level of Evidence: Prognostic Level IV.