No Weekend Effect in Elective Primary Total Knee Arthroplasty: A Nationwide Analysis of 437,121 U.S. Cases

Background: The "weekend effect" describes the possibility that patients treated on weekends experience worse outcomes because of differences in staffing, resource availability, and workflow. Evidence for a weekend effect in elective orthopedic surgery is limited, and most prior work does not isolate cases in which admission and surgery truly occur on the weekend. Methods: We performed a retrospective cohort study using the Nationwide Readmissions Database from 2020 to 2022. Adult patients undergoing elective primary total knee arthroplasty (TKA) with surgery on hospital day 0 were identified, yielding 437,121 admissions. Weekend admissions (Saturday to Sunday) were compared with weekday admissions (Monday to Friday). Baseline characteristics, in-hospital outcomes (length of stay, total hospital charges, mortality, and major postoperative complications) and 90 day outcomes (all cause readmission, time to readmission, readmission length of stay, and procedures during readmission) were compared using t tests and chi square tests. Results: Of all eligible cases, 435,822 (99.7 percent) occurred on weekdays and 1,299 (0.3 percent) on weekends. Baseline demographics, comorbidities, and hospital characteristics were highly similar between groups. In-hospital outcomes, including thromboembolic, renal, infectious, respiratory, and surgical complications, did not differ in a clinically meaningful way between weekday and weekend cases. Ninety day readmission rates, timing of readmission, readmission length of stay, and the need for procedures during readmission were also comparable. Conclusion: In this large contemporary national cohort of elective primary TKA with surgery on hospital day 0, weekend admission was not associated with worse in-hospital outcomes or higher 90 day readmission rates. These findings suggest that, within standardized perioperative pathways, elective TKA can be safely performed on weekends without a detectable weekend effect.