A Matched-Cohort Study Comparing Outpatient Total Knee Arthroplasty in An Ambulatory Surgery Center With Inpatient Total Knee Arthroplasty in a Hospital

Travis W. Littleton, MD; Anthony A. Mascioli, MD; Thomas W. Throckmorton, MD; William M. Mihalko, MD, PhD; Patrick C. Toy, MD


Curr Orthop Pract. 2020;31(5):474-478. 

In This Article

Abstract and Introduction


Background: The authors compared a matched cohort of outpatient total knee arthroplasties (TKA) performed in a free-standing ambulatory surgery center (ASC) with those performed in a standard inpatient hospital setting to determine the safety, efficacy, and expense associated with both locations.

Methods: Retrospective review identified 82 patients who had TKA, 41 at an ASC and 41 in an inpatient hospital. The cohorts were matched according to age and American Society of Anesthesiologists (ASA) physical status classification.

Results: There were no statistically significant differences in age, gender, body mass index, or ASA scores. There were no readmissions or major complications, including deep infection, periprosthetic fracture, or venous thromboembolism, in either cohort. Minor wound issues occurred in four (9.8%) hospital patients and one (2.4%) ASC patient. All ASC patients were discharged the day of surgery without an overnight stay. The average length of stay for the hospital group was 2.5 days. The average total facility charge for ASC patients was $26,800.00 compared to the national average of $31,124.

Conclusions: No significant differences were noted between TKA performed in an ASC and a hospital for major complications or hospital readmissions at 90 days. The average length of stay in the hospital was 2.5 days, however, which might indicate a higher cost than day surgery. Although not statistically significant, the ASC cohort had fewer minor complications than the inpatient cohort. In select patients TKA performed outpatient in an ASC appears to be as effective and safe as that performed in a hospital, with the caveat that some patients may not be candidates. Careful patient selection, preoperative screening and counseling, and the use of multimodal pain regimens are critical to minimizing complications and reducing costs.

Level of Evidence: Level III.


Total knee arthroplasty (TKA) is one of the most common operations in orthopaedics and is a well-established surgical intervention that provides both pain relief and improved function in patients with knee osteoarthritis. Historically, the average inpatient length of stay (LOS) in the United States following TKA was 10.7 days in 1995 compared to only 4.4 days in 2007. Increasing amounts of data have shown that shortened LOS may decrease perioperative complications and costs associated with arthroplasty procedures as well as heighten patient satisfaction.[1–3] In healthcare today, there is a growing emphasis on safety, efficiency, and cost-effectiveness. Performing arthroplasty procedures in an ambulatory surgery center (ASC) is a viable option to decrease overall healthcare cost while keeping the procedure safe and effective.[4,5] Successful outpatient knee arthroplasty has been reported, and several authors have described day of surgery (DOS) discharge in patients with both UKA and TKA.[1,6,7]

To better understand the possible advantages of TKA in an ASC setting, the authors compared a matched cohort of outpatient TKAs performed in a free-standing, privately-owned ASC with those performed in a standard inpatient hospital setting. This study was performed after January 2018, when Medicare removed TKA from the inpatient-only list, allowing these surgeries to be performed either inpatient or outpatient. The authors specifically set out to determine the safety, efficacy, and expense associated with both locations, as well as the difference in costs. The hypothesis was that TKA done in an ASC with same-day discharge would be as safe as TKA done in an inpatient setting and that the costs of TKA in an ASC would be comparable to published costs of traditional in-hospital TKA.