Why Are Some Patients Poor Candidates for Outpatient TKA?
Dr. Patawut Bovonratwet and Dr. Michael Ast answer ICJR’s questions about their study that evaluated the 30-day readmission rate following outpatient primary total knee arthroplasty, as well as the risk factors contributing to readmission, using the NSQIP database.
ICJR: What questions did you and your co-authors want to answer with this study?
Patawut Bovonratwet, MD: We attempted to answer several important questions about outcomes of outpatient total knee arthroplasty (TKA) with this study:
- What are the incidence, timing, and most common reasons for 30-day readmission in outpatient TKA patients?
- What are the perioperative risk factors for 30-day readmission in these patients?
- Would patients at high risk for 30-day readmission benefit from an inpatient hospital stay?
ICJR: What did you conclude?
Dr. Bovonratwet: Overall, patients are at low risk of 30-day readmission after outpatient TKA. However, we identified 3 factors that put patients at high risk of 30-day readmission: dependent functional status, chronic obstructive pulmonary disease (COPD), and prolonged operative time. Some of these high-risk patients were less likely to be readmitted if they had an overnight stay and seemed to benefit from an inpatient hospital stay. In addition, the majority of readmissions were non-surgical site related, which may provide opportunities for targeted intervention.
ICJR: How did you reach your conclusions? What was your study cohort and what did you find with your analysis?
Dr. Bovonratwet: Our study cohort included 3015 patients in the National Surgical Quality Improvement Program (NSQIP) dataset who had undergone outpatient TKA (defined as length of stay equal to 0 days) between 2012 and 2017. Briefly, the NSQIP database collects more than 150 perioperative variables from more than 500 participating institutions in the US. Trained clinical reviewers extract patient information using a variety of methods, including medical chart review, through the 30th postoperative day, regardless of day of discharge.
The incidence of 30-day readmission in this cohort was 2.59%, with an average time from surgery to readmission of approximately 2 weeks. Most readmissions (64%) were not related to the surgical site and included thromboembolic and gastrointestinal complications. As mentioned above, risk factors for 30-day readmission included dependent functional status prior to surgery (relative risk [RR]=6.4), COPD (RR=2.4), and operative time ≥ 91 minutes (≥ 70th percentile) (RR=1.9).
The 30-day readmission rate was significantly reduced for patients who had some of these risk factors if they had stayed at least 1 night at the hospital:
- For patients with dependent function status, the risk of 30-day readmission after outpatient TKA was significantly reduced if they had stayed in the hospital for 2 nights instead of being discharged the same day as surgery (RR=0.2).
- For patients with operative time ≥ 91 minutes, the risk of 30-day readmission was significantly reduced if they had stayed in the hospital for 1 night (RR=0.7).
ICJR: Why are these findings significant for clinical practice?
Michael P. Ast, MD: Multiple healthcare groups, including the Centers for Medicare and Medicaid Services (CMS), have a growing interest in using outpatient primary TKA as a means to reduce costs and increase efficiency. CMS, for example, removed TKA from the Inpatient-Only List for Medicare-covered patients in 2018 and now reimburses for it under the Medicare Hospital Outpatient Prospective Payment System and the Ambulatory Surgical Center Payment System.
However, although numerous studies have compared complication rates and costs between outpatient versus inpatient TKA, few studies have helped identify suitable candidates for outpatient pathways. Our study is among the first to identify patients who may not be a good fit for outpatient TKA due to higher 30-day readmission risk.
Our data can be used by surgeons when determining which patients could safely undergo outpatient TKA, as well as when counseling patients about their appropriateness for outpatient TKA pathways. In addition, this information serves to advise third-party payers that certain patients should not be pushed toward same-day discharge because of their significantly increased risk for readmission, which could ultimately increase costs due to complications following discharge.
Bovonratwet P, Shen TS, Ast MP, Mayman DJ, Haas SB, Su EP. Reasons and risk factors for 30-day readmission after outpatient total knee arthroplasty: a review of 3,015 cases (Paper 241). Presented at the 2021 Annual Meeting of the American Academy of Orthopaedic Surgeons, August 31-September 3, San Diego, California.
Bovonratwet P, Shen TS, Ast MP, Mayman DJ, Haas SB, Su EP. Reasons and risk factors for 30-day readmission after outpatient total knee arthroplasty: a review of 3,015 cases. J Arthroplasty. 2020 Sep;35(9):2451-2457. doi: 10.1016/j.arth.2020.04.073. Epub 2020 Apr 28.
About the Experts
Patawut Bovonratwet, MD, is an orthopaedic surgery resident at Hospital for Special Surgery, New York, New York. Michael P. Ast, MD, is an Assistant Professor of Orthopaedic Surgery, specializing in adult reconstruction and joint replacement, at Hospital for Special Surgery, New York, New York. He is also the Chief Medical Innovation Officer and Vice Chair, Innovation, at Hospital for Special Surgery.
Disclosures: Dr. Bovonratwet has no disclosures relevant to this article. Dr. Ast has disclosed that he receives royalties from, has stock or stock options in, is paid consultant for, and is a paid presenter or speaker for OrthAlign; that he has stock or stock options in HS2, OssoVR, and Parvizi Surgical Innovations; that he is a paid consultant for BD, ConformMIS, and Surgical Care Affiliates; that he is a paid consultant for, a paid presenter or speaker for, and receives research support from Smith & Nephew; and that he is a paid consultant for and a paid presenter or speaker for Stryker.