Determinants of ninety day readmission after elective primary total knee arthroplasty: A nationwide readmissions database study of 437,121 cases

Ninety day readmission after total knee arthroplasty (TKA) is a key quality and cost metric in value based care. Recent work in Arthroplasty Today has highlighted the role of mental health and machine learning based prediction, but contemporary national data focusing exclusively on elective primary TKA with full ninety day follow up remain limited. We analyzed the Nationwide Readmissions Database for 2020 to 2022. Adult patients undergoing elective primary TKA with surgery on the calendar day of admission were included. Revision, bilateral, nonelective, fracture, malignancy, infection, and COVID 19 related cases were excluded. Only discharges from January through September were used to ensure complete ninety day follow up. The primary outcome was ninety day all cause readmission. Multivariable logistic regression identified independent predictors. We identified 437,121 elective primary TKAs. Mean age was 67.6 ± 9.5 years and 61.2 percent were women. Robotic assisted TKA accounted for 9.9 percent and navigation guided TKA for 6.0 percent of procedures. The ninety day readmission rate was 5.3 percent. Periprosthetic infection (12.6 percent), gastrointestinal disorders (12.3 percent), cellulitis and soft tissue infection (11.5 percent), respiratory issues (11.0 percent), and cardiac events (9.8 percent) were the most common causes. Independent predictors included age, type 2 diabetes, chronic kidney disease, chronic lung disease, heart failure, prior stroke, prior myocardial infarction, peripheral vascular disease, fibromyalgia, and blood loss anemia during index admission. Female sex, obesity, dyslipidemia, robotic assistance, and navigation guidance were associated with lower odds of readmission. Ninety day readmission after elective primary TKA is infrequent but driven by a mixture of orthopedic and systemic medical complications. High risk comorbidity clusters and perioperative blood loss anemia are important targets for optimization. Computer assisted techniques showed a modest protective association. Level III