Outpatient Primary Total Hip Arthroplasty Is a Safe Alternative to Inpatient Primary Total Hip Arthroplasty: A Matched-Cohort Analysis Study

Introduction: Outpatient primary total hip arthroplasty (THA) accounts for approximately 8% of all total hip arthroplasties (THA) performed annually in the United States. As of 2020, Medicare removed THA from its inpatient-only list, allowing reimbursement as an outpatient procedure. This study aimed to determine whether outpatient primary THA is a potential alternative to inpatient procedures by assessing: 1) 90-day post-operative complications; 2) readmission rates; and 3) total costs of care. Materials and Methods: Using a national database, a matched case-control study was conducted of primary THAs performed between January 1, 2008 and March 31, 2018. Outpatient primary THAs were identified (n=10,463) and matched in a 1:5 ratio to inpatient primary THAs (n=52,306) for age, sex, and comorbidities. Outcomes assessed were 90-day medical complications, readmissions, and associated total costs of care. Baseline demographics were compared using Pearson's chi-squared analyses, with multivariate logistic regressions to calculate odds ratios (ORs) and 95% confidence intervals (CIs). Results: Patients undergoing outpatient THA had fewer 90-day complications (9.3 vs. 11.9%; OR: 0.80, 95% CI: 0.74 to 0.87, p<0.0001) relative to the inpatient cohort. Ninety-day readmission rates between outpatient and inpatient THAs were similar (4.1 vs. 4.8%; OR: 0.92, 95% CI: 0.83 to 1.03, p=0.166). Ninety-day costs were significantly lower for the outpatient cohort ($2,650.00 vs. $19,299.00, p<0.0001). Conclusion: Our study includes a large sample size of outpatient primary THAs and is the first to provide data quantifying cost differences relative to inpatient THAs. Our results suggest, in certain populations, that outpatient primary THAs are a safe alternative to inpatient procedures with the potential to decrease healthcare costs.