Table 1.

Main results of outpatient total knee arthroplasty (TKA) in the literature

Authors	Year	Results	Comments from the original publications
Berger et al18	2005	A total of 48/50 patients (96%) chose to go home the day of surgery. No intraoperative complications occurred. There were three readmissions, none related to early discharge: gastrointestinal haemorrhage at eight days, superficial irrigation and debridement at 21 days and a closed manipulation at nine weeks.	This study demonstrated that, in these selected patients, outpatient TKA was safe, with no short-term readmission or complications related to early discharge. This comprehensive pathway might make it possible for this minimally invasive TKA to be performed as an outpatient procedure in specialized surgicentres in the future.
Berger et al19	2009	Of 111 patients, 104 (94%), 24 with unicompartmental knee arthroplasty (UKA) and 80 with TKA met discharge criteria and were discharged directly to home the day of surgery. Nausea requiring additional treatment before discharge was the most common reason for a delay in discharge. There were four (3.6%) readmissions (all with TKA) and one emergency room visit without readmission (in a patient with a TKA) within the first week after surgery, whereas there were four subsequent readmissions (3.6%) and one additional emergency room visit without readmission within three months of surgery, all among patients undergoing TKA. There were no deaths, cardiac events, or pulmonary complications during this study.	Outpatient knee arthroplasty surgery is feasible in a large percentage of patients, yet early readmissions might be decreased with a prolonged hospitalization. Level IV of evidence.
Lovald et al3	2014	TKA patients were identified in the Medicare 5% sample (1997–2009) and separated into the following groups: outpatient, 1–2 days, 3–4 days, or 5+ days inpatient. At two years, costs associated with the outpatient and the 1–2 day stay groups were US$8527 and $1967 lower than the 3–4 day stay group, respectively. At two years, the outpatient and 1–2 day stay groups reported less pain and stiffness, respectively, although the 1–2 day stay group also had a higher risk for revision.	NA
Lovald et al20	2014	The Medicare 5% limited data set sample was used to identify patients with a TKA procedure who were treated in an outpatient setting or who were discharged within one or two days in the hospital setting. Rehospitalization risk increased with higher CCI (i.e. poorer health status), older patients, inpatients (vs. outpatients), patients not receiving a femoral nerve block, earlier (vs. recent) year of surgery and those with a recent history of heart failure.	The findings of this study suggest that current comorbidities, particularly heart failure, have the greatest effect on event risk after outpatient and short-stay TKA. The information obtained from this study should assist with patient selection for TKA performed on an outpatient basis.
Pollock et al7	2016	Systematic review. Of the 17 included studies, four were cohort studies with a control group and 13 were case series. All four cohort studies indicated that the complication rates and clinical outcomes were similar between the inpatient and outpatient groups. Furthermore, the three studies that involved an economic analysis indicated that outpatient arthroplasty is financially advantageous.	In selected patients, outpatient THA, TKA, and UKA can be performed safely and effectively. The included studies lacked sufficient internal validity, sample size, methodological consistency and standardization of protocols and outcomes. There is a need for high-quality prospective cohort studies and randomized trials to definitively assess the safety and effectiveness of outpatient THA, TKA and UKA.
Lovecchio et al13	2016	These authors compared outpatient arthroplasty and fast-track inpatient arthroplasty. All patients undergoing THA or TKA between 2011 and 2013 were selected from the American College of Surgeons-National Surgical Quality Improvement Program database. A propensity score was used to match 1476 fast-track ( ≤ 2 day length of stay) inpatients with 492 outpatients (3:1 ratio). Thirty-day complication, reoperation, and readmission rates were compared, both during and after hospitalization. After matching, outpatients had higher rates of medical complication (anytime, 10.0% vs. 6.7%). Most complications were bleeding requiring transfusion, which occurred at similar rates after surgery but at higher rates post discharge in outpatients (anytime, 7.5% outpatients vs. 5.6% inpatients; post discharge, 4.1% outpatients vs. 0.1% inpatients). There was no difference in readmission rate (2.4% outpatient vs. 2.0% inpatient).	Outpatients experience higher rates of post-discharge complications, which may countermand cost savings. Surgeons wishing to implement outpatient TJA clinical pathways must focus on preventing post-discharge medical complications to include blood management strategies.
Springer et al21	2017	A retrospective review of 137 patients undergoing outpatient TJA and 106 patients undergoing inpatient (minimum two-day hospital stay) TJA was conducted. Unplanned hospital readmissions and unplanned episodes of care were recorded. All patients completed a telephone survey. Seven inpatients and 16 outpatients required hospital readmission or an unplanned episode of care following hospital discharge. Readmission rates were higher for TKA than THA. The authors found no statistical differences in 30-day readmission or unplanned care episodes.	NA
Courtney et al22	2017	Of the total 169,406 patients who underwent TJA, 1220 were outpatients (0.7%). The outpatient and inpatient groups had an overall complication rate of 8% and 16%, respectively. Patients aged older than 70 years, those with malnutrition, cardiac history, smoking history or diabetes mellitus were at higher risk for readmission and complications after THA and TKA. Surprisingly, outpatient TJA alone did not increase the risk of readmission or reoperation, and was a negative independent risk factor for complications.	With the resources available in a hospital setting, outpatient TJA might be a safe option, but only in select, healthier patients. Care should be taken to extrapolate these results to an outpatient facility, where complications might be more difficult to manage.
Huang et al23	2017	In every case-control match, the SDD TKA was less costly than the inpatient procedure and yielded median cost savings of approximately 30%. The savings came primarily from costs associated with the inpatient encounter, such as surgical ward, pharmacy and patient meal costs. At one year, there were no major complications and no returns to hospital or readmission encounters for either group.	These results were consistent with previously published data on the cost savings associated with short-stay or outpatient TKA. In carefully selected patients, outpatient TKA is a feasible alternative to traditional inpatient TKA and is significantly less costly. Furthermore, it was deemed to be safe in the perioperative period.
Bovonratwet et al24	2017	Patients who underwent primary, elective TKA were identified in the 2005–2014 American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database. A total of 112,922 TKA patients met the inclusion criteria. Of these, only 64 (0.57%) were outpatient procedures. Outpatients tended to be men, slightly younger and have less comorbidity. After propensity matching, a multivariate analysis revealed a higher rate of postdischarge blood transfusions (P < .001) in the outpatient cohort. There were no other significant differences in 30-day postoperative individual adverse events or readmissions.	Based on the perioperative outcome measures studied here, outpatient TKA can be appropriately considered in select patients based on rates of overall perioperative adverse events and readmissions. However, higher surveillance of these patients postdischarge might be warranted.
Gromov et al4	2017	Of the 557 patients who were referred to the participating surgeons during the study period, 54% were potentially eligible for outpatient surgery. Actual DOS discharge occurred in 13–15% of the 557 patients. Female sex and surgery late in the day increased the odds of not being discharged on the DOS.	This study showed that even in unselected THA and TKA patients, SDD is feasible in approximately 15% of patients.
Arshi et al14	2017	Cohorts of 4391 patients who underwent outpatient TKA and 128,951 patients who underwent inpatient TKA were identified. The median age was in the 70- to 74-year age group in both cohorts. The incidence of outpatient TKA increased across the study period. After adjustment for age, sex, and CCI, outpatient TKAs were found to more likely be followed by tibial and/or femoral component revision due to a non-infectious cause, explantation of the prosthesis, irrigation and debridement and stiffness requiring manipulation under anaesthesia within one year. Outpatient TKA was also more frequently associated with postoperative deep vein thrombosis and acute renal failure.	Nationwide data from a private insurance database demonstrated a higher risk of perioperative surgical and medical complications in outpatient TKA than inpatient TKA, including component failure, surgical site infection, knee stiffness and deep vein thrombosis. Level III of evidence.
Courtney et al25	2018	Of the 49,136 Medicare-aged TKA patients, 365 (0.7%) were outpatient, 3033 (6%) were short-stay and 45,738 (93%) were inpatient. Short-stay patients had a lower complication rate than both the outpatient and inpatient groups (2% vs. 8% vs. 8%, respectively). Independent risk factors for experiencing a complication or requiring an inpatient stay include female sex, general anaesthesia, diabetes mellitus, chronic obstructive pulmonary disease, hypertension, kidney disease, ASA Score 4, body mass index > 35 kg/m2 and age > 75 years.	TKA can be performed safely as an outpatient in a subset of healthy Medicare patients with a complication rate similar to an inpatient stay. A 23-hour stay, however, might be the ‘sweet spot’ that minimizes complications in this population.
Gauthier-Kwan et al26	2018	A comparative cohort study of 43 inpatients (43 TKAs) and 43 outpatients (43 TKAs). Quality of recovery (QoR) was similar in the outpatient TKA group compared with the inpatient group. No statistically significant differences were observed for Knee Injury and Osteoarthritis Outcome Score and Western Ontario and McMaster Universities Osteoarthritis Index subscores. There was one readmission in both the outpatient and inpatient groups. Six inpatients and eight outpatients returned to the emergency department for any reason within 90 days, with no significant differences observed between the two groups.	Outpatient TKA in selected patients produced similar short-term and two-year patient-reported outcome measures and a comparable 90-day postdischarge hospital resource use compared with an inpatient cohort, supporting further investigation into outpatient TKA.
Husted et al27	2018	This study presented baseline detailed economic calculations of outpatient THA and TKA in two different settings: one from the hospital and another from the ambulatory surgery department. Patients and methods: Data from six patients (1 TKA, 1 uncemented THA, 1 cemented THA in each department) were collected prospectively using the Time Driven Activity Based Costing method (TDABC). Time consumed by various staff members involved in patient treatment in the perioperative period of outpatient THA and TKA was calculated in two different settings: one in the orthopaedic department and one in the ambulatory surgery department. Length of stay (LOS) was approximately 11 hours in the orthopaedic department and approximately seven hours in the ambulatory surgery department. TDABC revealed minor differences in the operative settings between departments, and similar expenses occurred during the short stay of US$777 and US$746, respectively. Adding the preoperative preparation and postoperative follow-up resulted in total costs of US$951 and US$942 for the ward and the ambulatory surgery department, respectively.	Outpatient THA and TKA in the hospital and ambulatory surgery departments results in similar cost using the TDABC method. Compared with the cost associated with two-day stays, outpatient procedures are approximately two-thirds cheaper, provided no increase occurs in complications or readmissions.
Cassard et al28	2018	Of 574 patients, 61 were selected to undergo outpatient TKA and 513 had inpatient TKA. The day-30 readmission rate was 2/61 (3.3%) in the outpatient group and 25/513 (4.9%) in the inpatient group. The overall complication rate was 8.0% for the outpatients and 7.2% for the inpatients. The satisfaction rate was high in the outpatient group, with 80% very satisfied and 20% satisfied patients.	When performed in appropriately selected patients, outpatient TKA is not associated with a higher readmission rate compared with inpatient TKA.
Shah et al8	2018	These authors evaluated 30-day and 90-day complication rates in patients who underwent outpatient TJA. Of the 90-day complication events, there were two patients (2%) with postoperative arthrofibrosis of the knee after TKA requiring manipulation under anesthesia, one postoperative patellar tendon rupture during therapy after TKA requiring surgical repair and one delayed hematogenous infection after international travel after THA requiring two-staged exchange.	Outpatient TJA with discharge to home is a safe option after development of a multidisciplinary TJA pathway.
Gogineni et al6	2018	This study analysed 105 consecutive patients who underwent THA or TKA following a newly implemented outpatient arthroplasty protocol. These authors compared these patients to a group of inpatient arthroplasty patients from the same time period. Eighty-three of 105 (79%) patients were successfully discharged home on the DOS. Successful same-day discharge was predicted by early ambulation, TKA over THA, and shorter duration of surgery. General anaesthesia correlated with better early ambulation distances and a lower incidence of urinary retention. The outpatient readmission and complication rates were 0.95% and 1.9%, respectively, whereas the matched inpatient rates were 3.7% and 2.9%, respectively.	Outpatient THA and TKA in a well-selected patient is feasible in an academic multidisciplinary tertiary care hospital, with complication rates approximating inpatient surgery.
Bilgen et al15	2019	This report anaylsed 31 patients (three male, 28 female), with a mean age of 67 years, who underwent TKA. The mean LOS was 28.7 hours and mean duration of surgery was 92 minutes. Combined spinal epidural anaesthesia was performed for 23 (74.2%) patients and general anaesthesia was used in eight (25.8%) patients. Among the 31 patients, 23 (74.2%) patients were discharged within 23 hours of surgery.	Early discharge of patients following outpatient surgery for TKA was not associated with any procedure-related complications among the selected patients up to three months postoperatively.
Gromov et al16	2019	In this study all consecutive and unselected patients scheduled for THA or TKA at two participating hospitals were screened for potential DOS discharge. Patients who fulfilled the DOS discharge criteria were discharged home. Patients discharged on DOS were matched on preoperative characteristics using propensity scores to patients operated on at the same two departments prior to the beginning of this study with at least one overnight stay. All readmissions within 90 days were identified. It was possible to match 116 of 138 outpatients with 339 inpatient controls. Median LOS in the control cohort was two days. Seven (6%) outpatients and 13 (4%) inpatient controls were readmitted within 90 days. Readmissions occurred between postoperative day 2–48 and day 4–58 in the outpatient and control cohorts, respectively. Importantly, we found no readmissions within the first 48 hours and no readmissions were related to the DOS discharge.	Readmission rates in patients discharged on DOS may be similar to matched patients with at least one overnight stay. With the selection criteria used, there may be no safety signal associated with same-day discharge.
Crawford et al17	2019	These authors analysed the incidence of complications associated with outpatient TKA and also the two-year minimum results. In 124 procedures, the patient stayed overnight for 23-hour observation. Thirty-seven (3.2%) were for convenience reasons and 87 (7.6%) for medical observation. Heart disease and chronic obstructive pulmonary disease were associated with increased risk of overnight stay. Excluding manipulations, reoperation within 90 days occurred in eight (0.7%) knees. Patients with two-year minimum follow-up had significant improvements in range of motion, Knee Society Clinical, Functional and Pain scores. Nine (0.8%) patients required revision. Manipulations were performed on 118 (10.3%) patients. The overall deep infection rate was 0.17% (2/1143).	Outpatient TKA is safe for a large proportion of patients. Certain medical comorbidities increase the risk of overnight stay. Patients had significant improvement in range of motion and outcome scores with low revision rate.

Note. NA, not available; UKA, unicompartmental knee arthroplasty; THA, total hip arthroplasty; TJA, total joint arthroplasty; SDD, same-day discharge; DOS, day of surgery; CCI, Charlson Comorbidity Index; ASA, American Society of Anesthesiologists; QoR, Quality of recovery; LOS, length of stay.