Establishing the Minimally Important Difference for the KOOS–Joint Replacement and PROMIS Global–10 in Patients After Total Knee Arthroplasty

Abstract

Background: Despite the overall prevalence and success of total knee arthroplasty (TKA), a significant portion of patients are dissatisfied with their outcomes. Purpose: To assess the responsiveness and determine the minimally important difference (MID) of 2 patient-reported outcome measures (PROMs)—the Knee injury and Osteoarthritis Outcome Score–Joint Replacement (KOOS-JR) and the Patient-Reported Outcomes Measurement Information System Global–10 (PROMIS 10)—in patients after TKA. Study Design: Cohort study (diagnosis); Level of evidence, 3. Methods: Included were patients who underwent TKA from August 2015 through August 2019 and completed baseline and postoperative KOOS-JR and PROMIS 10 surveys. The PROMIS 10 consists of 2 domains: physical health and mental health. Estimates for the reliable change index (RCI) and MID, using anchor-based and distribution-based methods, were calculated for each PROM. Regression modeling was used to determine whether patient and clinical factors predicted MID thresholds or MID achievement. Results: A total of 1315 patients were included. Distribution-based MIDs, calculated using various methods from baseline scores, ranged from 19.3 to 31 for the KOOS-JR, and the RCI was 4.38. Of these patients, 293 (22.3%) demonstrated small or moderate improvement, and this cohort was included in the calculation of anchor-based MIDs. The anchor-based MIDs were 16.9 and 24.3 at 3-month and 1-year follow-up, respectively, and 66% of patients achieved the MID at 12 months. Higher preoperative PROM score, male sex, non-White race, and current smoker status were predictive of failing to achieve the anchor-based MID for KOOS-JR at 1 year postoperatively ( P < .05). Higher preoperative PROM score and any 90-day adverse event predicted lower thresholds of important change in anchor-based MIDs. Higher baseline PROM scores, younger age, male sex, non-White ethnicity, higher American Society of Anesthesiologists classification, preoperative narcotics use, not smoking, and longer hospital stay were all associated with lower odds of achieving the MID on the KOOS-JR or either of the PROMIS 10 subscales. Conclusion: The study results demonstrated relevant values for interpretation of the KOOS-JR and PROMIS 10. While patient demographics did not accurately predict which patients would achieve the MID, some potential factors predicting successful patient-reported outcomes after TKA were identified.