Safety of outpatient vs. inpatient anterior cervical discectomy and fusion: a systematic review and meta-analysis

Introduction

With the rising cost of health care around the world, interest has developed in reducing expenditure by several means like, use of generic drugs, remote care pathways, minimizing hospital stay, and improving healthcare financing systems (Cohn, 2014). Of these, remote care pathways and outpatient surgery are rapidly being incorporated in clinical practice. Remote care via telemedicine encompasses consultations by videoconferencing or telephone is now being utilized for orthopedic referrals. This encompasses patients who do not necessitate a thorough physical, internal, or visual examination. Remote consultations reduce the need for medical personnel to travel in certain circumstances, thereby reducing costs (Moldovan & Moldovan, 2025). On the other hand, outpatient surgery provides numerous benefits, such as expedited recovery periods, increased convenience, and reduced costs. Patients frequently experience reduced tension and are able to recuperate in the privacy and comfort of their own homes. Furthermore, the more predictable schedules of ambulatory settings can be advantageous for both patients and medical personnel (Zhang et al., 2024).

Anterior cervical discectomy and fusion (ACDF) is routinely used to treat degenerative cervical spine conditions, including cervical radiculopathy and myelopathy (Song & Choi, 2014). Historically, ACDF has been performed in an inpatient setting due to concerns over postoperative complications, including dysphagia, hematoma, and respiratory distress (Song & Choi, 2014; Gould, Sohail & Haines, 2019; Narain et al., 2020). However, due to advancements in surgical techniques, anesthesia, and perioperative care, there is a growing interest in outpatient ACDF that may provide several advantages, such as reduced healthcare costs, lower risk of nosocomial infections, and enhanced patient satisfaction (Erickson et al., 2007; Rossi et al., 2020; Safaee et al., 2021). However, while outpatient ACDF is associated with potential cost savings and is generally considered safe, there is still limited data on its safety and the impact on patient outcomes.

Previous reviews and meta-analyses have highlighted the need for further synthesis and evaluation of the evidence (Ban et al., 2016; McClelland et al., 2016; Yerneni et al., 2020; Epstein, 2021). Ban et al. (2016) evaluated the safety of outpatient ACDF compared to inpatient surgery using a meta-analysis of 12 studies. They concluded that outpatient ACDF is a cost-effective method that is equally safe and has a similar risk of complications as inpatient surgery if postoperative complications are closely monitored (Ban et al., 2016). More recently, the meta-analysis of 15 studies by Yerneni et al. (2020) indicated no significant difference in the incidence of overall complications, stroke, dysphagia, thrombolytic events, and hematoma between outpatient and inpatient ACDF. However, rates of reoperation, mortality, as well as length of hospitalization were significantly lower in cases of outpatient ACDF. The study concluded that while outpatient ACDF can be safe for well-selected patients, those with advanced age and comorbidities may not be suitable (Yerneni et al., 2020). The most recent review focused on studies published up to April 1, 2018 (Yerneni et al., 2020). Since then, several high-quality studies with large sample sizes have been published, providing valuable evidence on a broader range of previously unexplored outcomes. This study aims to provide an updated comprehensive summary and analysis of the evidence comparing the safety of outpatient and inpatient ACDF. The research question was: Does outpatient ACDF lead to similar risk of mortality and complications as compared to inpatient ACDF?

Methods

This systematic review strictly adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (Page et al., 2021). The protocol was preregistered in the PROSPERO database (CRD42025636625).

Study screening and final selection process

All identified studies were deduplicated. Two reviewers (MY & WY) independently assessed each title and abstract using the predetermined eligibility criteria. The literature screening was done from 5th February until 10th February 2025. An inter-rater reliability assessment was performed during the initial screening to evaluate consistency in study selection, with a predefined acceptable threshold of 80%. If the agreement fell below this threshold, the senior author (LD) would have convened a detailed discussion to ensure clarity and alignment regarding the inclusion and exclusion criteria. However, this step was not required, as the inter-rater reliability reached approximately 92%.

For studies that passed the title and abstract screening, a full-text review was conducted to confirm final eligibility. If discrepancies arose during either phase, they were resolved through a structured consensus process. Initially, the two reviewers (MY & WY) engaged in discussion to reassess the study, carefully cross-referencing it with the eligibility criteria and prior decisions. If the discrepancy was due to unclear reporting, additional details from Supplementary Materials, study protocols, or cited references were reviewed to ensure an informed decision. In cases where consensus could not be reached after discussion, the senior author (LD) was consulted to provide an independent evaluation and make the final determination. PRISMA flow diagram of the study is shown in Fig. 1.

Results

Of 269 identified studies (Fig. 1), 53 duplicates were removed, and the titles and abstracts of 216 unique records were inspected. Of them, 179 studies were eliminated as not meeting the review’s objectives. The full texts of the 37 studies were evaluated. Eventually, 21 studies (Stieber et al., 2005; Liu, Briner & Friedman, 2009; Martin et al., 2014; McGirt et al., 2015; Adamson et al., 2016; McClelland et al., 2017; Fu et al., 2017; Khanna et al., 2018; Purger et al., 2018; Purger et al., 2019; Mullins et al., 2018; Arshi et al., 2018; Vaishnav et al., 2019a; Vaishnav et al., 2019b; Patel et al., 2019; Shenoy et al., 2019; Khalid et al., 2019; Boddapati et al., 2021; Lee et al., 2021; Kamalapathy et al., 2021; Tani et al., 2023) were incorporated in the final analysis (Table 1).

The included studies provided data from 164,541 patients, of whom 36,361 were treated as outpatients, and 128,180 as inpatients. All the studies had a retrospective cohort design and were done in the United States of America (Table 1). The inpatient groups tended to be older and exhibit a higher comorbidity burden, as reflected by higher American Society of Anesthesiologists (ASA) classification (often ASA ≥3) and/or Charlson Comorbidity Index (CCI) scores. The outpatient groups, in contrast, were generally younger, with fewer comorbidities. Many studies examined one- or two-level ACDF in both groups (17 out of 21 included studies). Where reported, BMI was comparable between groups, though a few studies indicated higher obesity rates in the inpatient group (Table 1). The postoperative outcomes were primarily assessed within 6 months post-operatively (19 out of 21 studies). Most studies demonstrated moderate-to-high methodological quality (score of 6 and above) based on their NOS assessments (Table 1; Table S2). The mean NOS score was 7.2.

Risk of complications

Compared to the inpatient ACDF group, patients undergoing outpatient/ambulatory procedures had reduced risk of “any” complications (RR 0.45, 95% CI [0.35–0.57]; n = 14, I² = 74.7%) and mortality (RR 0.35, 95% CI [0.16–0.77]; n = 7, I² = 0.0%) (Fig. 2). Furthermore, these patients had a lower risk of deep vein thrombosis (DVT) (RR 0.56, 95% CI [0.37–0.85]; n = 8, I² = 39.6%). However, the risk of stroke/cerebrovascular accident (CVA) and dysphagia was similar in both groups (Fig. 3). Patients undergoing outpatient ACDF had reduced risk of wound complications (infection and/or dehiscence) (RR 0.59, 95% CI [0.52–0.68]; n = 8, I² = 0.0%) and reduced need for blood transfusion (RR 0.21, 95% CI [0.09–0.48]; n = 5, I² = 55.0%) (Fig. 4). The estimated blood loss (in ml) (WMD −13.6, 95% CI [−20.2 to −7.0]; n = 4, I² = 72.1%) and the length of hospital stay (in hours) (WMD −22.3, 95% CI [−40.1 to −4.5]; n = 6, I² = 100.0%) was also lesser in the outpatient group (Fig. S1). However, the risk of developing hematoma was similar between the groups (Fig. 4).

The risk of unplanned reoperation (RR 0.33, 95% CI [0.24–0.46]; n = 9, I² = 19.0%), readmission (RR 0.57, 95% CI [0.46–0.70]; n = 10, I² = 62.4%) and reintubation (RR 0.47, 95% CI [0.27–0.81]; n = 5, I² = 0.0%) was substantially reduced in outpatient ACDF group (Fig. 5). While the risk of progressive renal insufficiency, acute renal failure, and cardiac complications was similar in both groups, the outpatient ACDF was associated with a reduced risk of pulmonary complications (pneumonia, pulmonary embolism, ventilator dependence) (RR 0.43, 95% CI [0.27–0.68]; n = 9, I² = 88.7%) (Fig. 6). The risk of developing sepsis (RR 0.56, 95% CI [0.49–0.64]; n = 6, I² = 0.0%) and urinary tract infection (UTI) (RR 0.34, 95% CI [0.20–0.60]; n = 7, I² = 59.7%) was lower in the outpatient group, compared to inpatient subjects (Fig. 7).

Discussion

This meta-analysis synthesizes evidence from 21 studies encompassing 164,541 patients, comparing the outcomes of outpatient and inpatient ACDF. The findings demonstrate that outpatient ACDF correlates with a significantly lower risk of overall complications, mortality, DVT, wound complications, and the need for blood transfusion. Additionally, outpatient ACDF was linked to a lower length of hospital stay, estimated blood loss, and lower risks of unplanned reoperation, readmission, reintubation, incidences of pulmonary complications, sepsis, and UTI. However, risks of stroke/CVA, dysphagia, hematoma, and renal and cardiac complications were comparable between the two groups.

Our findings align with earlier reviews, including those by Ban et al. (2016) and Yerneni et al. (2020), which highlighted the safety of outpatient ACDF for appropriately selected patients. However, this study updates the field by incorporating ten additional recent studies and examining a broader spectrum of outcomes, thereby providing a more comprehensive evaluation of outpatient ACDF safety.

While this meta-analysis demonstrated the safety of ACDF as an outpatient procedure, it is important to take into account the quality of the evidence while interpreting the results. The mean NOS score of the studies was 7.2, indicating moderate quality. All studies were retrospective in nature and hence, the possibility of selection bias, i.e., healthier patients being chosen for outpatient procedures cannot be neglected. This was evident in the comparison of baseline characteristics wherein the outpatient cohort was younger and had fewer comorbidities. In some studies (Adamson et al., 2016), outpatient procedure was conducted, initially, only in those patients who had the lowest risk of postoperative complications and gradually extended to more complex cases. Boddapati et al. (2021) have reported that in the USA, in 2018, only 32.9% of three-level ACDF were conducted in an outpatient setting and surgeons still carried out four-level procedures in an in-patient setting, given the more complex nature of the surgery and higher tendency of complications. There has been an increasing trend of conducting two-level and three-level procedures in an outpatient setting, however, data is still limited (Boddapati et al., 2021). The study by Arshi et al. (2018) also reported that high-risk cases like elderly patients or those undergoing multi-level procedures still have significantly higher complication rates in an outpatient setting. This suggests that patient selection is still critical while deciding to perform ACDF as an outpatient or an inpatient procedure. Baseline comorbidities, age, ASA grade, etc would remain essential factors in selection of patients till more quality evidence from randomized controlled trials is made available. The present study could not conduct a subgroup analysis for high-risk patients due to lack of data. We believe that future studies should stratify patients as high-risk and low-risk categories to better assess the safety of ACDF as an outpatient procedure.

Many factors may explain the observed associations between outpatient ACDF and reduced complication rates. Patient selection plays a critical role, as outpatient ACDF patients are typically younger, healthier, and have fewer comorbidities, which collectively lower their baseline risk of complications. Additionally, outpatient facilities often adhere to enhanced perioperative protocols to ensure rapid recovery and early discharge, thereby reducing risks such as infection and sepsis (Smith et al., 2020). The shorter hospital stays associated with outpatient procedures could further minimize exposure to hospital-acquired infections, including pneumonia and UTIs. Lastly, the surgical and anesthetic stress experienced by outpatient ACDF patients is generally lower due to shorter procedures, reduced blood loss, and decreased anesthetic exposure, which may help reduce risks of DVT and pulmonary embolism (Phan et al., 2017).

This study has some limitations. There was substantial (I² > 70%) heterogeneity in some outcomes, such as length of stay and estimated blood loss, likely reflecting differences in study populations, definitions of outcomes, and reporting standards. Additionally, the retrospective cohort design of all included studies introduces inherent risks of bias, such as unmeasured confounders and potential selection bias. For example, healthier patients are more likely to undergo outpatient procedures, skewing results in favor of outpatient ACDF.

We could not conduct a more detailed subgroup analysis in our study stratifying patients based on age, comorbidities, and complexity of surgery as segregated data was unavailable. Furthermore, the GRADE assessment revealed that the certainty of the evidence was low to very low for most outcomes due to high heterogeneity, risk of bias, and indirectness of the evidence. These limitations underscore the need for high-quality prospective studies or randomized clinical trials to strengthen the evidence base.

While our findings support the safety of outpatient ACDF, clinicians should consider patient-specific factors such as age, comorbidities, and surgical complexity when determining the appropriate surgical setting. The reduced risk of complications and shorter recovery times in outpatient settings suggest that this approach might be a cost-effective and patient-centered option if appropriate perioperative care protocols are followed. Given the low certainty of evidence on GRADE, high-quality prospective cohort studies and randomized controlled trials are needed to provide reliable comparisons between outpatient and inpatient settings. Standardizing outcome definitions and reporting protocols will ensure consistency across studies. Studies should stratify outcomes based on the number of comorbidities and complexity of the case so that the benefits of out-patient surgery are clearly delineated. Additionally, future investigations should explore long-term outcomes, such as fusion success rates and chronic complications, to comprehensively understand the risks and benefits of outpatient ACDF. Research into the biological and clinical mechanisms underlying outcome differences could offer valuable insights to optimize surgical practices.

Conclusion

This meta-analysis suggests that outpatient ACDF may be associated with fewer complications as compared to inpatient procedures in carefully selected patients. However, the findings should be interpreted cautiously as they are based on retrospective cohort studies, which are inherently prone to selection bias, and have a low to very low certainty of evidence. While outpatient ACDF demonstrates promising outcomes, careful patient selection and adherence to standardized perioperative protocols remain critical to ensure safety and efficacy. In the absence of robust randomized controlled trials, evidence from retrospective studies remains speculative.

Supplemental Information