An Examination of the Adoption of Outpatient Total Knee Arthroplasty Since 2018

J Arthroplasty. 2020 Jun;35(6S):S24-S27. doi: 10.1016/j.arth.2020.01.073. Epub 2020 Feb 4.


Background: The Centers for Medicare and Medicaid Services removed total knee arthroplasties (TKAs) from the inpatient-only (IPO) list on January 1, 2018, which meant that TKAs could be performed on a hospital outpatient basis. We examined the following: (1) the national rate of adoption of outpatient TKAs over time, (2) how adoption varied across hospitals, and (3) whether adoption of outpatient TKAs has positively or negatively impacted 90-day TKA readmission rates.

Methods: We used national patient-level Medicare Fee-for-Service Part A claims data (100% sample) from January 2017 through June 2019 to look at the quarterly trend in percent of TKAs performed as outpatient, and the distribution in this percentage across hospitals in the country. We ran a case-level regression to understand whether inpatient vs outpatient coding status relates to 90-day readmission rates.

Results: In 2017 prior to the removal of TKAs from the IPO list, 0.2% were performed as outpatient. In the first quarter (Q1 2018) after the rule change, 24.9% were performed as outpatient, and by the second quarter of 2019, 36.4% were performed as outpatient. These rates varied widely across hospitals from 0% (10th and 25th percentiles) to 78% (90th percentile) from January 2018 through March 2019. There was no difference in readmission rates for same-day discharges, but outpatient cases discharged after one or more nights in the hospital had statistically lower readmissions than inpatient cases.

Conclusion: There was a rapid increase in the adoption of hospital outpatient TKAs following their removal from the Medicare IPO, which has resulted in lower readmission rates, and so adoption is likely to continue.

Keywords: inpatient-only list; length of stay; medicare; outpatient; readmission; total knee arthroplasty.

MeSH terms

  • Aged
  • Arthroplasty, Replacement, Knee*
  • Humans
  • Inpatients
  • Medicare
  • Outpatients
  • Patient Discharge
  • Patient Readmission
  • United States