Defining the Minimal Clinically Important Difference and Patient Acceptable Symptom State for Isolated Microfracture of the Knee at 5-Year Follow-up.

Background: There is a paucity of literature regarding the long-term clinical significance and patient-reported outcome measures (PROMs) after isolated microfracture of the knee for cartilage defects. Purposes: To (1) define the minimally clinically important difference (MCID) and patient acceptable symptom state (PASS) thresholds for knee microfracture at a minimum 5-year follow-up, and (2) investigate predictive factors-including preoperative, demographic, and intraoperative variables-to achieve MCID and PASS. Study Design: Case-control study; Level of evidence, 3. Methods: All patients who underwent isolated microfracture for knee chondral defects from 2013 to 2018 were retrospectively identified through a prospectively-maintained institutional database. MCID thresholds were determined by a distribution-based method, while PASS thresholds were established using an anchor-based method. The PROMs analyzed included the International Knee Documentation Committee (IKDC) score and the Knee injury and Osteoarthritis Outcome Score (KOOS). Multivariate logistic regression was performed to identify factors associated with achieving the MCID and PASS thresholds. Results: A total of 70 patients were included in the study. The thresholds for MCID achievement and achievement rates were as follows: IKDC, 11.13 (68.57%); KOOS activities of daily living (ADL), 10.56 (65.71%); KOOS Pain, 9.83 (72.86%); KOOS quality of life (QoL), 14.47 (67.14%); KOOS Sport, 14.65 (68.57%); and KOOS Symptoms, 9.95 (58.57%). The thresholds for PASS achievement and achievement rates were as follows: IKDC, 67.24 (58.57%); KOOS ADL, 96.31 (44.29%); KOOS Pain, 85.54 (51.43%); KOOS QoL, 56.38 (55.71%); KOOS Sport, 57.41 (55.71%); and KOOS Symptoms, 76.74 (54.29%). A lower preoperative score was predictive of achieving the MCID for the IKDC and each KOOS subscale. A Kellgren-Lawrence (K-L) grade of 0 or 1 was predictive of achieving the PASS for the IKDC, KOOS Pain, and KOOS Symptoms. A lower body mass index (BMI) was predictive of achieving the PASS for the KOOS ADL and the KOOS Pain, in addition to attaining the MCID for the KOOS ADL, KOOS Pain, and KOOS Sport. A lesion size of <2 cm Conclusion: This study defines the thresholds for MCID and PASS achievement at a minimum 5-year follow-up for patients undergoing isolated microfracture of the knee. Patient-specific and defect-specific factors associated with MCID and PASS achievement included lower BMI, younger age, male sex, lower K-L grade, and smaller lesion sizes.