Discordance in Published 30-Day Readmission Rates Following Primary Total Hip and Total Knee Arthroplasty: Centers for Medicare and Medicaid Services (CMS) Versus the National Surgical Quality Improvement Program (NSQIP).

Background: 30-day readmission is an important quality metric evaluated following primary total joint arthroplasty (TJA) that has implications for hospital performance and reimbursement. Differences in how 30-day readmissions are defined between Centers for Medicare and Medicaid Services (CMS) and other quality improvement programs (i.e., National Surgical Quality Improvement Program [NSQIP]) may create discordance in published 30-day readmission rates. The purpose of this study was to evaluate 30-day readmission rates following primary TJA using two different temporal definitions. Methods: Patients undergoing primary total hip and primary total knee arthroplasty at a single academic institution from 2015-2020 were identified via common procedural terminology (CPT) codes in the electronic medical record (EMR) and institutional NSQIP data. Readmissions that occurred within 30 days of surgery (consistent with definition of 30-day readmission in NSQIP) and readmissions that occurred within 30 days of hospital discharge (consistent with definition of 30-day readmission from CMS) were identified. Rates of 30-day readmission and the prevalence of readmission during immortal time were calculated. Results: In total, 4,202 primary TJA were included. The mean hospital length of stay (LOS) was 1.79 days. 91% of patients were discharged to home. 30-day readmission rate using the CMS definition was 3.1% (130/4,202). 30-day readmission rate using the NSQIP definition was 2.7% (113/4,202). Eight readmissions captured by the CMS definition (6.1%) occurred during immortal time. Conclusion: Differences in temporal definitions of 30-day readmission following primary TJA between CMS and NSQIP results in discordant rates of 30-day readmission.