Risk Factors and Thresholds for Minimal Clinically Important Difference in Worsening after Unicompartmental Knee...

The rising demand for unicompartmental knee arthroplasty (UKA) in the United States has led to high 1-year patient satisfaction rates. However, some patients experience substantial declines in patient-reported outcome measures (PROMs) postoperatively, which we refer to as "minimal clinically important difference for worsening" (MCID-W). We sought to define MCID-W values for specific PROMs and identify risk factors associated with PROMIS Physical Function Short Form 10a (PROMIS PF-10a) declines after UKA. We conducted a retrospective study of 760 patients undergoing UKA at our institution between 2016 and 2023. Preoperative and postoperative PROMIS PF-10a, PROMIS global physical, and knee injury and osteoarthritis outcome score-physical function short-form (KOOS-PS) scores were collected. Patients were stratified upon reaching minimal clinically importance difference for improvement (MCID-I), MCID-W, or "no significant change" (score between MCID-W and MCID-I). MCID-W and MCID-I values were determined using a distribution-based method. Logistic regression was performed to identify risk factors for scoring below MCID-W. We established the following MCID-I and MCID-W thresholds: PROMIS PF-10a (+3.00 and -1.64), KOOS-PS (+6.25 and -3.42), and PROMIS Global-Physical (+2.72 and -1.55). Bivariate analysis revealed differences in terms of revision (p = 0.02), reoperation (p = 0.03), postoperative complications (p = 0.002), deep venous thrombosis (DVT; p < 0.001), and pneumonia (p = 0.01) between cohorts. Body mass index >35 (odds ratio [OR] = 2.49), postoperative complications (OR = 5.09), pneumonia (OR = 22.39), DVT (OR = 9.27), and preoperative PROMIS PF-10a scores (OR = 1.07) were risk factors for scoring below the MCID-W threshold, whereas age > 80 (OR = 2.89) and preoperative PROMIS PF-10a scores (OR = 1.05) were risk factors for failing to achieve MCID-I. Our study established MCID-W values for pivotal PROMs after primary UKAs. We found that 8.8% of patients scored below MCID-W, highlighting the need to improve patient selection and perioperative care in UKA.