1 Introduction

Total knee arthroplasty (TKA) is one of the most effective solutions to restore function and quality of life in patients with disabling knee osteoarthritis. For TKA to be cost-efficient and safe for patients, numerous studies and guidelines have been developed with the aim of reducing inpatient stay while at the same time minimising complications.¹

Enhanced Recovery After Surgery (ERAS) is one such guideline that is gaining increasing popularity and adoption in surgical centres worldwide. The concept of ERAS evolves around 4 important concepts: a multidisciplinary patient-centric care; multimodal approach tackling post-operative complications and delayed recovery; protocols backed by evidence-based medicine; and continuous audits to improve protocols.² Originally described for coronary artery bypass and sigmoid resection, ERAS protocol has seen rapid adoption and success in numerous other surgical fields.^3–7 The basis of ERAS emphasises that patient care peri-operatively is equally important compared to the actual surgery in determining patient outcomes, and evidence-based protocols have been developed by the ERAS society for surgical centres to implement in their transition.⁸

As ERAS TKA often involves expedited discharge after operation, careful patient selection has been advocated for it to be safe and efficacious. Various patient factors and health status have been identified as negative predictors for early discharge,^9–14 and these may preclude some patients from the benefits of an enhanced recovery.

In this study, the authors explored the success and safety of ERAS protocol in conjunction with a Day-surgery protocol on some commonly used selection criteria for expedited discharge after Total Knee Arthroplasty (TKA).

2 Methods

Institutional Review Board approval was obtained for this study (CIRB Ref: 2022/2166). Reporting is performed based on Reporting on ERAS Compliance, Outcomes, and Elements Research (RECOVER) Checklist¹⁵ and Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.¹⁶

Patients who underwent ERAS Day surgery TKA between August 2020 and July 2021 in the authors institution were followed up. Inclusion criteria were: 1. Patients agreeable for discharge home; 2. unilateral primary TKA; and 3. ASA ≤3.

ERAS TKA was done as Day surgery, and patients were planned for discharge within 24 h post-operation. Guidelines from ERAS Society consensus statements⁸ was implemented in line with hospital protocols. Discharge to home within 24 h of surgery was considered successful completion of ERAS Day surgery TKA protocol. All patients received inpatient physiotherapy sessions focusing on range of motion exercises and strengthening as well as gait and mobility aid training prior to discharge. The protocol also consisted of: 1. home visit by physiotherapist at 1week post-operation; and 2. home visit by nurse at 2 weeks post-operation. Patients were also advised to continue their therapy exercises independently at home and were referred to an outpatient physiotherapist in the primary care setting near their place of residence 1 month after discharge to monitor their progress. Complications such as infection, re-admission, and re-operation within 30-days were recorded.

Patient demographics and comorbidities such as gender, age, Charlson Comorbidity Index (CCI), Body Mass Index (BMI), and American Society of Anaesthesiologist Classification (ASA) were analysed between patients who were successfully discharged within 24 h and those with prolong admission, and between those with and without complications.

Patient were reviewed pre-operatively and at 6 months post-operation and Patient Reported Outcome Measures (PROM) such as Oxford Knee Score (OKS), Knee Society Score (KSS), and mental and physical component score (MCS and PCS) of 36-Item Short-Form Health Survey (SF-36) were recorded.

3 Results

342 patients who underwent ERAS Day surgery TKA during the study period were included. The common medical comorbidities in the study population are shown in Table 1. The mean surgical time was 88.6 (±20.1) minutes and the average time from completion of surgery to ambulating ≥10 m was 11.8 (±0.8) hours. 92.1 % of patients were discharged within 24 h s and were considered as successful completion of ERAS Day surgery protocol. 7.9 % of patients had prolonged stay of more than 24 h s and were considered as failure of protocol. The most frequent cause for prolonged stay was inadequate pain control (17.9 %), patient decision for transfer to community hospital for rehabilitation after surgery (17.9 %), nausea and vomiting (7.1 %), and acute retention of urine (7.1 %). 48.1 % of the patients with delayed discharge beyond 24 h s were discharged on post-operative day 2, 49.5 % on post-operative day 3, and only 2.4 % of patients had hospitalisation of ≥ 3days. Patients who passed ERAS Day surgery protocol had similar characteristics such as gender, age, surgical side, ASA, BMI, and CCI compared to those with delayed discharge (Table 2).

30-days readmission rate was 2.6 % (9 patients). 5 patients (1.5 %) presented with infection within 30-days, consisting of 2 surgical site infection resolved with antibiotics, 2 prosthetic joint infection (PJI) (0.6 %) that underwent debridement, antibiotics, and implant retention (DAIR), and 1 case of pneumonia. Re-operation rate within 30-days was 0.9 % (3 patients), including the 2 DAIR and 1 patient who underwent aspiration of the knee joint which was negative for infection. Male gender was associated with an increased incidence of infection and all re-operation occurred in male patients (Table 3). None of the 30-days readmission, infection, and re-operation occurred in patients who initially failed ERAS Day surgery TKA.

Binary logistic regression model was constructed to ascertain the effect of age, gender, CCI, ASA class, and BMI on the probability that patients might: 1. Pass or fail ERAS Day surgery protocol; 2. 30-days readmission; 3. 30-days infections; 4. 30-days re-operation. The logistic regression model was statistically insignificant for all 4 end-points (Passing or failing ERAS protocol (x2(5) = 4.837, p = 0.436), 30-days readmission (x2(5) = 5.757, p = 0.331), 30-days infection (x2(5) = 6.344, p = 0.274), and 30 days re-operation (x2(5) = 8.998, p = 0.109)). None of independent variables contributed significantly to the model (Table 4).

Patient who passed or failed ERAS Day-surgery TKR protocol all experienced significant improvement in their quality of life and functional outcome scores(Table 5) with increase in scores above the Minimal Clinically Important Difference (MCID) (4.3–5 points for OKS,¹⁷ 5.3 to 5.9 points for KSKS, 6.4 points for KSFS¹⁸).

Propensity score matching in which 27 patients who pass ERAS Day surgery protocol were matched to the 27 patients who failed protocol based on age, gender, CCI, ASA classification, and BMI failed to demonstrate and statistically significant difference in PROM (Table 6).

4 Discussion

This study found no significant factors that influences rate of successful 24 h discharge with ERAS Day-surgery protocol or post-operation complication. Importantly, even if patients who were enrolled in an ERAS Day-surgery protocol initially failed to be discharged within 24 h, there were no increased 30-days complication rates or difference in 6-month PROMs.

ERAS TKA has been implemented with tremendous success across the world and large registry data have validated its safety and efficacy. Garriga et al.¹⁹ analysed the United Kingdom (UK) National Joint Registry and Hospital Episode Statistics (HES) databases around the period of April 2009 when ERAS program was introduced by the Department of Health and noted that mean Length of Stay (LOS) reduced to 3.7 days from 5.8 days, translating to a bed-day cost saving of £2331. There was also a decrease in complication rate from 4.1 % to 1.7 % while the revision rate remained unchanged at 4.8 % per 1000 implant years. 131 hospitals in Spain also participated in the Postoperative Outcomes Within Enhanced Recovery After Surgery Protocol in Elective Total Hip and Knee Arthroplasty (POWER2) Study Investigators Group for the Spanish Perioperative Audit and Research Network (REDGERM)²⁰ and found that ERAS group of patients had an average LOS of 4 days compared to non-ERAS patients with a LOS of 5 days. No differences in terms of complications, readmission, reinterventions, or survival were noted between the 2 groups of patients. In the authors’ institution, the median cost for ERAS Day surgery TKA is ∼$10,527USD, compared to $12,625USD for conventional TKA, which amounts to a cost reduction of 17 %.

Day surgery TKA has been gaining increasing popularity especially in times of increasing healthcare constrains. In United States (US), there had been a significant decrease in LOS for TKA comparing 2012 (2.9 days) to 2021 (1.3 days).²¹ For ERAS Day surgery to be successful, not only does patient discharge need to be fulfilled in an expedited and timely manner, there also need to be no compromise in patient outcome and safety. Various studies have been conducted to predict patients who will not be suitable for this protocol. The American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database has been a great source of information for many clinicians seeking to analyse factors that might predict patient outcome. Using the 2014–2015 ACS-NSQIP database, Courtney et al.¹² compared patients who underwent outpatient, short-stay (24 h discharge), and inpatient TKA and found those that patients who are male, had lower BMI, lower rate of diabetes, chronic obstructive pulmonary disease, and hypertension were more likely to complete short-stay TKA. The longest study based on ACS-NSQIP conducted between 2005 and 2014 by Bovonratwet et al.¹⁰ noted that age, ASA≤ 2, and male gender were significant predictor of discharge within the same day. Lopez et al.¹³ developed a model for patient selection for outpatient Total Joint Arthroplasty (TJA) using ACS-NSQIP data from 2010 to 2018 and found predictive variable for same day discharge included age <70 years, male gender, white race, BMI <30, ASA ≤2, and non-smoker. Although these large registry studies have provided useful information on potential factors that might influence discharge rate, a non-discriminatory application will likely exclude a large population of patients who might potentially benefit from ERAS Day surgery. If an inclusion criterion of BMI ≤30, ASA ≤2, and age <70 was applied, 60.5 % of patients in this study who would have benefited from ERAS would have been excluded. By combining the multidisciplinary and multimodal approach of ERAS and day surgery protocol, the authors did not find any significant association between gender, age, ASA classification, BMI, and CCI on predicting patient discharge.

Whilst registry data are useful by providing a longitudinal data of large sample size that provide generalizable evidence applicable to the real-world usage, the heterogeneity of institutional and surgeon practice may introduce potential source for bias and confounders. Comparative studies aim to minimise this by isolating patient factors as the only variable.

Berger et al.⁹ achieved 96 % success rate of same day discharge after TKA in their study population with an exclusion criteria of patients with pulmonary embolism, myocardial infarction, anticoagulation therapy, BMI >40 kg/m², and having 3 or more comorbidities. In another study conducted by Kolisek et al.²² with a stringent criteria that excluded patients with comorbidities such as stroke, myocardial infarction, diabetes, venous thromboembolism, congestive heart failure, or chronic opioid use, 100 % of TKA patients were discharged within 23 h. Although stricter selection criteria will likely lead to higher early discharge rate, this will limit its benefit to a smaller group of patients. Riding on the success of their previous study, Berger et al.²³ expanded the inclusion of day surgery TKA and Unicompartmental Knee Arthroplasty (UKA) to an unselected group of patients and still managed to achieve a 94 % success rate on same day discharge and found the main reason for delay to discharge was difficulty with pain control. Similarly, in this study, with a limited exclusion criteria of ASA ≥4, 92.1 % of TKA patients were successfully discharged within 24 h, and the most common cause for delayed discharge was also inadequate pain control (17.9 %). Using patient comorbidities to predict successful ERAS Day surgery is not an exact science. The Outpatient Arthroplasty Risk Assessment (OARA) score was recently published by Meneghini et al.²⁴ as a tool to allow surgeons to predict if patients would be suitable for same day or next day discharge. However, there are limited studies available to validate the score. Crawford et al.²⁵ found that even though OARA had good predictive value for patients who might be discharged on the same day, its ability to determine patients who might not was lacking, giving rise to the same issue of restricting patients who would be potential candidates for outpatient arthroplasty. This study highlights an important finding that even if patient were enrolled into ERAS Day surgery protocol but failed to be discharged within 24 h, there were no increased 30-days complication rates and patient outcome did not differ at 6-month post-operatively. Therefore, it might be feasible to provide ERAS Day surgery to a wider group of patients without fear of complications arising from a more inclusive patient selection. By proving that ERAS Day surgery TKA is not only safe for the patients, but also more cost efficient that traditional inpatient TKA, valuable hospital resources could be better distributed to improve the cost-effectiveness of the healthcare system.

Although no association between gender, age, ASA classification, BMI and CCI on predicting patient discharge was identified in this study, there was a significantly higher incidence of infection and re-operation in male patients. Male gender as an independent risk factor for prosthetic joint infection after total joint arthroplasty has been well described in the literature. In an observational cohort study of 679 010 TKA from England and Wales, Lenguerrand et al.²⁶ found that male gender was associated with an increased risk of infection compared to female (RR 1.8, 95 % CI 1.7–2.0). In a systematic review and meta-analysis by Kunutsor et al.,²⁷ male gender was again identified as an independent risk factor for infection after total joint arthroplasty (RR 1.36, 95 % CI 1.18–1.57). The findings of this study showed that this increased risk of infection in male gender was also present in patients undergoing ERAS Day Surgery TKA. However, as this was not an isolated risk factors only associated with ERAS Day surgery TKA, this should not be used as an exclusion criterion for patient selection. Instead, this could serve as a basis for targeted preoperative intervention for male patients who presents with other potential risk factors for increased risk of prosthetic joint infection.

This study has to be interpreted in lights of its limitations. This study was performed in a single surgical centre with a relatively smaller cohort of patients compared to other multicentred or registry data. However, as all operations were carried out within the same centre, it was easier to ensure administrative process were followed and all patients were homogenous in the standard of care received. As ERAS protocol had only recently been implemented in the authors institution, longer follow up studies are needed to ascertain the role of ERAS Day surgery TKA in a patient's long-term outcome and implant survivorship. The strength of this study is that as data were collected prospectively for the conduct of this study, a wide range of parameters were included, which allowed for more meaningful analysis of patient outcomes to effectively evaluate the results of ERAS Day surgery TKA. As one of the first centres in Asia to introduce ERAS TKA, this study also described the application of ERAS protocol as well as its feasibility in the Asian population. The findings of this study would also serve as a platform to explore for potential solutions to address the correctable factors influencing successful discharge after ERAS Day surgery TKA such as improving post-operative pain control and reducing post-anaesthesia complications such as nausea and urinary retention. The positive results from this pilot study will form the basis to allow a broader inclusion of patients to the ERAS Day surgery TKA protocol in the authors institution.

5 Conclusion

Various selection criteria have been proposed in order for expedited discharge after TKA to be both cost-efficient and at the same time safe for patients. A stringent criterion might preclude many patients who might potentially benefit from an expedited discharge. In this study, no significant association between age, gender, CCI, ASA classification, BMI, and successful completion of ERAS Day surgery TKA or complication rates were noted. Failure of discharge within 24 h was also not associated with increased 30-days complication or poorer 6-month PROMs. Expanding the inclusion criteria for ERAS Day surgery TKA can allow more patients to benefit from this cost-efficient and safe protocol.

Ethical statement

Institutional Review Board approval was obtained for this study (CIRB Ref: 2022/2166).

Funding/sponsorship

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Guardian/patient's consent

Patient consent was exempted for the conduct of this study as this was a retrospective study approved by the institution review board (CIRB Ref: 2022/2166).

CRediT authorship contribution statement

Sheng Xu: Data curation, Formal analysis, Investigation, Methodology, Writing – original draft, Writing – review & editing. Ming Han Lincoln Liow: Conceptualization, Project administration, Resources, Supervision, Validation, Writing – review & editing. Xuan Eric Liu: Project administration, Validation, Writing – review & editing. Hee-Nee Pang: Conceptualization, Project administration, Resources, Supervision, Validation, Writing – review & editing. Shi-Lu Chia: Project administration, Resources, Supervision, Validation, Writing – review & editing. Keng Jin Darren Tay: Conceptualization, Project administration, Resources, Supervision, Validation, Writing – review & editing. Seng Jin Yeo: Conceptualization, Project administration, Resources, Supervision, Validation, Writing – review & editing. Jerry Yongqiang Chen: Conceptualization, Project administration, Resources, Supervision, Validation, Writing – review & editing, Each of the co-authors was involved in the design of the study, the interpretation of the data, and writing of the manuscript; and has read and concurs with the content in the manuscript.