Same-day versus overnight discharge after total knee arthroplasty: a national propensity-matched analysis of 90-day readmission and hospital charges

Same-day discharge (SDD) following total knee arthroplasty (TKA) has gained traction, particularly after the COVID-19 pandemic. However, large-scale post-pandemic evidence on safety and cost outcomes remains limited. This study evaluated 90-day readmissions and economic impact among patients discharged on the day of surgery versus those discharged after an overnight stay. Elective primary TKA admissions were identified in the 2020–2022 Nationwide Readmissions Database. Admissions involving fracture, infection, revision, oncologic diagnoses, bilateral TKA, or COVID-19 were excluded. Only procedures performed on admission day with a length of stay of 0 or 1 day were included. Propensity scores were estimated using demographic characteristics, comorbidities, robotic assistance, and hospital characteristics. Matching was performed on the unweighted discharge-level records using sequential greedy 1:1 nearest-neighbor matching without replacement and an absolute caliper of 0.1 on the propensity-score scale. NRD discharge weights were applied after matching to generate weighted national estimates. Because individual matched records carried different discharge weights, the reported weighted group totals were not numerically identical despite equal-sized underlying matched groups. The primary outcome was 90-day readmission. The eligible cohort represented 208,103 weighted elective primary TKA admissions, including 10,460 same-day discharge admissions and 197,643 overnight-stay admissions. After 1:1 matching of the underlying unweighted discharge records and subsequent application of NRD discharge weights, the matched cohort represented 10,460 same-day discharge admissions and 10,894 overnight-stay admissions nationally. Ninety-day readmission occurred in 3.4% and 4.0% of admissions, respectively, corresponding to a relative risk of 0.85 (95% CI 0.74–0.98) and an absolute risk difference of − 0.6% points (95% CI − 1.1 to − 0.1; p = 0.02). A coded surgical procedure during readmission occurred in 2.4% versus 1.9%, corresponding to a relative risk of 1.26 (95% CI 1.05–1.52) and an absolute risk difference of 0.5% points (95% CI 0.1–0.9; p = 0.007). Mortality during readmission, readmission length of stay, time to readmission, readmission charges, and index hospitalization charges were comparable between groups. In this matched observational analysis, same-day discharge was associated with a small absolute reduction in 90-day readmission and a similarly small absolute increase in coded surgical procedures during readmission. Other measured inpatient outcomes and hospital charges were comparable. These findings do not establish causal equivalence or universal safety and should be applied only to appropriately selected patients within structured perioperative pathways. Level II.