Comorbidity Burden Contributing to Racial Disparities in Outpatient Versus Inpatient Total Knee Arthroplasty

Introduction: Outpatient total knee arthroplasty (TKA) is increasingly common in the setting of early-recovery protocols, value-based care, and removal from the inpatient-only list by the Centers for Medicare & Medicaid Services. Given the established racial disparities that exist in different aspects of total joint arthroplasty, we aimed to investigate whether racial and ethnic disparities exist in outpatient compared with inpatient TKA.

Methods: This was a retrospective cohort study using the American College of Surgeons National Surgical Quality Improvement Program. We queried TKAs done in 2018. Demographics, inpatient (≥2 midnights) versus outpatient (≤1 midnight) status, comorbidities, and perioperative events/complications were recorded. We analyzed differences between racial/ethnic groups and predictors of inpatient versus outpatient surgery, and outcomes.

Results: A total of 54,582 patients were included (83.2% Caucasian, 9.2% African American [AA], 4.5% Hispanic, 2.4% Asian, and 0.6% Native American). AA had the highest mean body mass index, American Society of Anesthesiologists score, and comorbidity burden. AA had the lowest rate of outpatient TKA (18.3%) and Asians the highest rate of outpatient TKA (31.4%, P < 0.0001). AA had the highest postoperative transfusion rate (1.8%, P < 0.0001) and highest rate of discharge to acute rehab (8.4%). Asians had the highest rate of postoperative cardiac arrest and urinary tract infection. AA had the highest rate of acute kidney injury within 30 days. Regression analyses revealed that AAs were more likely to undergo inpatient surgery (odds ratio [OR], 2.58; confidence interval [CI], 1.57-4.23; P = 0.001) and discharge to rehab/skilled nursing facility [SNF] (OR, 2.86; CI, 1.66-4.92; P = 0.001). Asian patients were more likely to undergo outpatient surgery (OR, 2.48, CI, 1.47-4.18, P = 0.001) and discharged to rehab/SNF (OR, 2.41, CI, 1.36-4.25, P = 0.001). Caucasians were more likely to undergo outpatient surgery (OR, 1.62, CI, 1.34-1.97, P = 0.001) and less likely discharged to rehab/SNF (OR, 0.73, CI, 0.60-0.88, P = 0.001). When controlling for comorbidities, race was not an independent risk factor for 30-day complications or inpatient versus outpatient surgery.

Discussion: Differences in indications for outpatient TKA between races/ethnicities seem to be highly associated with comorbidity burden and preoperative baseline differences, not race alone. Appropriate patient optimization for either outpatient or inpatient TKA may reduce disparities between groups in either care setting.