Two-Day Length of Stay is Not Inferior to 3 Days in Total Knee Arthroplasty with Regards to 30-Day Readmissions Stefano A. Bini, MD a , Maria C.S. Inacio, PhD b , Guy Cafri, PhD, MStat b a Department of Orthopaedic Surgery, The Permanente Medical Group, 280 Macarthur Blvd, Oakland, CA b Surgical Outcomes and Analysis, Kaiser Permanente, 8954 Rio San Diego Drive, Suite 406, San Diego, CA abstract article info Article history: Received 11 July 2014 Accepted 2 December 2014 Keywords: total knee arthroplasty readmission length of stay non-inferiority risk factors The impact of a shortened length of stay (LOS) following total knee arthroplasty (TKA) on the risk of readmission is not well documented despite recent trends towards shorter hospitalization. We retrospectively compared the adjusted risk of 30-day readmission following TKA between patients with 2-, 3- and 4-day LOS using current postoperative care protocols. A total of 23,655 consecutive primary, unilateral TKAs operated between 01/01/ 2009 and 12/31/2011 were studied retrospectively using non-inferiority testing. The main outcome was 30-day readmission. Two-day LOS decreased the odds of readmission by a factor of 0.96, with an upper bound one-sided 95% confidence interval of 1.10. After adjusting for other variables, LOS of 2 days is not inferior to 3 days with respect to the risk of 30-day readmission. © 2014 Elsevier Inc. All rights reserved. Over the past decade, significant changes in the perioperative manage- ment of total joint arthroplasty (TJA) patients have occurred [1–4]. Some of these changes included implementation of clinical pathways, standardiza- tion of rehabilitation protocols, preoperative patient education protocols, and multimodal perioperative anesthetic and pain management strategies. The introduction of TJA pathways in the 1990s significantly reduced length of stay (LOS) to a national US average of 4.6 days [5] for primary total knee arthroplasty (TKA) and 4.7 days for primary total hip arthroplasty (THA) [6]. In 2003, Kim et al [1] reported favorably on the outcomes of the imple- mentation of pathways from this decade. In association with advances in multimodal pain management and accelerated rehabilitation protocols in the ensuing decade, LOS shortened considerably with a national average now approaching 3.8 days [7] and reports of successful same day surgery by some authors [8–10]. Furthermore, hospitals are seeing decreasing re- imbursements from insurers and are looking to improve resource utiliza- tion by minimizing LOS [11,12]. Recent studies evaluating LOS and readmissions focused on identify- ing risk factors for prolonged LOS [13–17] with the goal of risk stratify- ing these patients prior to admission. Other studies looked at factors associated with a shorter LOS [2–4,17] in an effort to identify best prac- tices in this area. Several studies have also evaluated the specific impact a shortened LOS has on short term clinical outcomes such as readmis- sion rates with the consistent conclusion that a shorter LOS is not asso- ciated with an increase in perioperative complications or readmissions [7,9,10,18–21]. However, in the larger studies, LOS was compared to a historical baseline that was generally over 3 days [7,21–23]. A few stud- ies have evaluated readmission rates following same day or 1-day LOS, but these had small sample sizes and these patients were treated by a limited number of surgeons in highly specialized centers [9,10,24]. Fur- ther, the majority of current readmission studies refer to patients treat- ed before 2009 and before wide adoption of multimodal pain management and early rehabilitation protocols described elsewhere [2–4,17,19,20]. It is therefore not clear from the current literature if a 2-day LOS confers no greater risk for readmission than a 3-day LOS in large patient populations treated with current postoperative protocols. Our primary aim was to determine if an LOS of 2 days following pri- mary TKA is not inferior to a 3-day LOS with respect to risk of 30-day re- admission rates. We also evaluated the impact of patient, surgeon, and hospital variables on the risk for 30-day readmission. Patients and Methods Study Design, Data Collection, Sample A retrospective analysis of a prospectively followed cohort of primary TKA was conducted using data from the Kaiser Permanente Total Joint Replacement Registry (KPTJRR). The registry records patients’ demo- graphics, implant characteristics, surgical techniques and outcomes in- cluding revisions, re-operations and infections. The patient sample is drawn from a large, integrated health care system present in 8 geograph- ical regions of the United States and including approximately 9.2 million people. Registry forms are validated using independent administrative databases and electronic screening algorithms described elsewhere [25–27]. Most KPTJRR outcomes are validated through chart reviews using predefined guidelines. Infections are identified using a previously The Journal of Arthroplasty 30 (2015) 733–738 One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2014.12.006. Reprint requests: Maria C. Inacio, PhD, Surgical Outcomes and Analysis, Kaiser Permanente, 8954 Rio San Diego Drive, Suite 406, San Diego, CA 92108. http://dx.doi.org/10.1016/j.arth.2014.12.006 0883-5403/© 2014 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org