Freestanding Ambulatory Surgery Centers and Patients Undergoing Outpatient Knee Arthroplasty.

Importance: In 2018, Medicare removed total knee arthroplasty from the list of inpatient-only procedures, resulting in a new pool of patients eligible for outpatient total knee arthroplasty. How this change was associated with the characteristics of patients undergoing outpatient knee arthroplasty at hospital-owned surgery centers (HOSCs) vs freestanding ambulatory surgery centers (FASCs) is unknown. Objectives: To describe the characteristics of patients undergoing outpatient, elective total and partial knee arthroplasty in 2017 and 2018 and to compare the cohorts receiving treatment at FASCs and HOSCs. Design, Setting, and Participants: This observational retrospective cohort study included 5657 patients having elective, outpatient partial and total knee arthroplasty in the Florida and Wisconsin State Ambulatory Surgery Databases in 2017 and 2018. Prior admissions were identified in the State Inpatient Database. Statistical analysis was performed from March to June 2022. Main Outcomes and Measures: Characteristics of patients undergoing surgery at a FASC vs a HOSC in 2017 and 2018 were compared. Results: A total of 5657 patients (mean [SD] age, 64.2 [9.9] years; 2907 women [51.4%]) were included in the study. Outpatient knee arthroplasties increased from 1910 in 2017 to 3747 in 2018 and were associated with an increase in total knee arthroplasties (474 in 2017 vs 2065 in 2018). The influx of patients undergoing outpatient knee arthroplasty was associated with an amplification of differences between the patients treated at FASCs and the patients treated at HOSCs. Patients with private payer insurance seen at FASCs increased from 63.4% in 2017 (550 of 867) to 72.7% in 2018 (1272 of 1749) (P < .001), while the percentage of patients with private payer insurance seen at HOSCs increased, but to a lesser extent (41.6% [427 of 1027] in 2017 vs 46.4% [625 of 1346] in 2018; P < .001). In 2017, the percentages of White patients seen at FASCs and HOSCs were similar (85.0% [737 of 867] vs 88.2% [906 of 1027], respectively); in 2018, the percentage of White patients seen at FASCs had increased and was significantly different from the percentage of White patients seen at HOSCs (90.6% [1585 of 1749] vs 87.9% [1183 of 1346]; P = .01). Both types of facilities saw an increase from 2017 to 2018 in the percentage of patients from communities of low social vulnerability, but this increase was greater for FASCs (FASCs: 6.7% [58 of 867] in 2017 vs 33.9% [593 of 1749] in 2018; HOSCs: 7.6% [78 of 1027] in 2017 vs 21.2% [285 of 1346] in 2018). Finally, while FASCs and HOSCs had cared for a similar portion of patients with prior admissions in 2017 (7.8% [68 of 867] vs 9.4% [97 of 1027], respectively; P = .25), in 2018, FASCs cared for fewer patients with prior admissions than HOSCs (4.0% [70 of 1749] vs 8.1% [109 of 1346]; P < .001). Conclusions: This study suggests that the increase in the number of patients undergoing outpatient knee arthroplasty in 2018 corresponded to FASCs treating a greater share of patients who were White, covered by private payer insurance, and healthier. These findings raise a concern that as more operations transition to the outpatient setting, variability in access to FASCs may increase, leaving hospital-owned centers to bear a greater share of the burden of caring for more vulnerable patients with more severe illness.