Abstract

Background: Morbid obesity (MO) is defined by the World Health Organization (WHO) as Class II (i.e. Body Mass Index (BMI) >/= 35 kg/M2 + 2 comorbidities) or Class III (i.e. BMI >/= 40 kg/M2). Here, we reviewed the rates for adverse event/s (AE)/morbidity/mortality for MO patients undergoing anterior cervical surgery as inpatients/in-hospitals, and asked whether this should be considered the standard of care?

Methods: We reviewed multiple studies to document the AE/morbidity/mortality rates for performing anterior cervical surgery (i.e., largely ACDF) for MO patients as inpatients/in-hospitals.

Results: MO patients undergoing anterior cervical surgery may develop perioperative/postoperative AE, including postoperative epidural hematomas (PEH), that can lead to acute/delayed cardiorespiratory arrests. MO patients in-hospitals have 24/7 availability of anesthesiologists (i.e. to intubate/run codes) and surgeons (i.e. to evacuate anterior acute hematomas) who can best handle typically witnessed cardiorespiratory arrests. Alternatively, after average 4-7.5 hr. postoperative care unit (PACU) observation, Ambulatory Surgical Center (ASC) patients are sent to unmonitored floors for the remainder of their 23-hour stays, while those in Outpatient SurgiCenters (OSC) are discharged home. Either for ASC or OSC patients, cardiorespiratory arrests are usually unwitnessed, and, therefore, are more likely to lead to greater morbidity/mortality.

Conclusion: Anterior cervical surgery for MO patients is best/most safely performed as inpatients/in-hospitals where significant postoperative AE, including cardiorespiratory arrests, are most likely to be witnessed events, and appropriately emergently treated with better outcomes. Alternatively, MO patients undergoing anterior cervical procedures in ASC/OSC will more probably have unwitnessed AE/cardiorespiratory arrests, resulting in poorer outcomes with higher mortality rates. Given these findings, isn't it safest for MO patients to undergo anterior cervical surgery as inpatients/in-hospitals, and shouldn't this be considered the standard of care?

Keywords: Anterior Cervical Surgery, Postoperative Epidural Hematomas (PEH), Risks, Adverse Events, Patient Selection, Morbid Obesity (MO), Contraindication Outpatient Surgery, Morbidity/Mortality, Cardiorespiratory Arrests, Witnessed, Unwitnessed

INTRODUCTION

Morbid obesity is defined as Class II (i.e. Body Mass Index >/= 35 kg/M2 + 2 comorbidities) and Class III (i.e. BMI >/= 40) by the World Health Organization (WHO) [ Table 1 ]. Specifically for MO patients undergoing anterior cervical surgery (i.e. mostly anterior cervical discectomy/fusion (ACDF), some anterior corpectomy/fusions (ACF), and cervical disc arthroplasties (CDR)), we looked at the frequencies of postoperative adverse events (AE), including acute/delayed cardiorespiratory arrests, and the resultant morbidity and mortality rates for inpatients [ Table 1 ]. We concluded, based on our review of MO patients undergoing anterior cervcial surgery as inpatients/in-hospitals, that this should be considered the standard of care.

Table 1:

Summary of Data.

1/1000 to 0.4-1.2% Incidence of Postoperative Spinal Epidural Hematomas (SEH) Following Anterior Cervical Surgery

Two studies looked at varying frequencies of postoperative SEH following anterior cervical surgery (i.e. 1/1000 to 0.4-1.2^%) [ Table 1 ].[ 15 , 21 ] Schroeder et al. (2017) looked at 16,582 cervical spine operations performed at 23 centers (2005-2011); for the 15 (i.e. 0.09% nearly 1/1000) postoperative spinal epidural hematomas (SEH), they recommended early diagnosis and treatment to optimize recoveries.[ 21 ] Miao et al. (2018) found 15 cases of postoperative hematomas following cervical spine surgery, citing seven retropharyngeal hematoms (RPH in 0.5%), and eight postoperative spinal epidural hematomas (SEH in 0.6%).[ 15 ] Patients with higher BMI and/or MO, those with OPLL (ossification of the posterior longitudinal ligament), longer operative times, and multilevel surgery were all at increased risk for SEH.[ 15 ]

Advantages of Inpatient/In-Hospital Treatment for Acute Postoperative Anterior Cervical Hematomas

The protocols for treating acute postoperative anterior cervical hematomas may include; (A) immediate opening of wounds in the postoperative care unit (PACU) (i.e. for patients in severe acute distress, especially where intubation is extremely difficult), and (B) obtaining STAT postoperative MR scans followed by returns to the operating room to remove documented hematomas. Additionally, MO inpatients who develop postoperative AE, especially including increased focal swelling/edema, exacerbation of obstructive sleep apnea, and/or postoperative epidural hematomas (PEH) as inpatients/in-hospital settings, have 24/7 availability of anesthesiologists (i.e., to intubate, run codes and resuscitate), and surgeons (i.e. to evacuate anterior acute hematomas). Alternatively, after typical 4-7.5 hr. postoperative care unit (PACU) observation periods, Ambulatory Surgical Center (ASC) patients are sent to unmonitored floor beds for up to the remaining 23-hour stays, while Outpatient SurgiCenter (OSC) patients are discharged home. For ASC/OSC patients, cardiorespiratory arrests result in more devastating neurological sequelae and/or death (i.e. Advanced Cardiac Life Support (ACLS) Data Show Significant Brain Damage for CPR Delayed 4-6 minutes, and High Probability of Brain Damage if Delayed 6-10 minutes).

Two Case Studies of Acute Returns to the Operating Room Without MR Scans Missed Hematomas

Following ACDF, 2 case studies documented how immediate returns to the operating room without postoperative MR scans failed to correctly diagnose the locations of postoperative hematomas [ Table 1 ].[ 7 , 18 ] In Hans et al. (2003) study, 2.5 hours following a C67 ACDF, the patient developed acute flaccid quadriplegia; they immediately returned to the operating room without a repeat MR to remove a presumed anterior C67 PEH.[ 7 ] However, when they failed to find the clot, they then obtained a STAT MR that demonstrated a posterior PEH that warranted an immediate C3-T3 laminectomy. In the second case (2016), following a C56 ACDF, the patient developed acute postoperative paraparesis; the immediate return to the operating room without an MR failed to reveal an anterior C56 PEH.[ 18 ] The patient subsequently underwent a STAT cervical/thoracic MR that demonstrated a thoracic subdural hematoma that was acutely treated with a thoracic laminectomy.

Patients With Fewer/More Minor Comorbidities Were “Carefully Selected” for ACDF Surgery in ASC/OSC

Several studies showed that patients with fewer/more minor comorbidities were “carefully selected” to undergo ACDF surgery in ASC/OSC, while most with MO/other major comorbidities were typically triaged to undergo ACDF surgery as inpatients [ Table 1 ].[ 5 , 14 , 24 ] Garringer et al. (2010) retrospectively assessed unplanned readmissions within 48 postoperative hours in a population of 645 patients undergoing 1-level ACDF in ASC/OSC; 2 (0.3%) acutely developed postoperative spinal epidural hematomas diagnosed in postoperative care units (PACU) within 4-hour post-surgery windows.[ 5 ] However, there were 6 other unplanned readmissions that occurred following the 4-hour PACU observation period; 80% were for postoperative pain/nausea. Using a PearlDiver Database, Martin et al. (2018) evaluated the number/severity of postoperative adverse events occurring within 30 days of 18,386 ACDF performed in inpatient vs. outpatient settings (2007-2014).[ 14 ] There was a lower AE rate of 9.5% for ACDF performed as outpatients vs. an 18.6% incidence of AE for inpatients who had more severe comorbidities (i.e. higher incidence of obesity, older age, coronary, renal, and pulmonary disease). These authors concluded, “Appropriate patient selection is key, and the standard of care nationally for the comorbid patient remains inpatient admission.” When Yerneni et al. (2020) evaluated the safety of performing ACDF in an outpatient setting (i.e. based on 21 review articles up to 2018), they determined that only; “...well-selected patients should undergo outpatient ACDF”.[ 24 ] Notably, they specifically “selected” to perform inpatient ACDF procedures for those with greater/more severe comorbidities, typically including; significant obesity, older age, and myelopathy that predisposed these patients to higher reoperation rates, longer lengths of stay (LOS), and greater mortality. They concluded that those with greater comorbidities; “are likely not suitable (candidates) for outpatient ACDF.”

Definition of Obesity and Morbid Obesity

The World Health Organization defines Obesity as Class II (>/= 35 kg/M2 + 2 comorbidities) vs. Morbid Obesity as Class III (>/= 40 kg/M2: MO World Health Organization) [ Table 1 ].[ 2 , 3 , 6 , 9 , 12 , 13 , 16 , 22 ]

Greater Comorbidities in Obese/MO Patients Undergoing ACDF Lead to More Postoperative Adverse Events (AE)/Morbidity/Mortality

Multiple studies documented greater postoperative AE, morbidity, and mortality rates for obese/MO patients undergoing anterior cervical surgery, particularly ACDF [ Table 1 ].[ 1 , 3 , 6 , 10 , 16 , 17 , 19 , 20 ] At 2 postoperative years in Chotai et al. (2016), MO Class II (BMI >/= 35 mg/M2) and Class III patients (40 kg/M2) exhibited greater comorbidities, more adverse events (AE), lower Quality-Adjusted Life Years (higher cost per QALY), and lower cost-effectiveness following ACDF surgery vs. non-obese patients.[ 1 ] In Epstein’s review in 2017, most spine studies documented the increased risks of major AE for morbidly obese patients (i.e. Classes II or III) undergoing spine surgery.[ 3 ] Their higher risks included; poor quality preoperative studies, poor resolution of intraoperative films resulting in more wrong-level surgery, more vascular compromise (i.e., deep venous thrombosis (DVT)/pulmonary embolism (PE)), more cardiac events, plexus/positioning injuries, blindness in the prone position, wound hematomas, seromas, and anesthetic AE (i.e. due to obstructive sleep apnea and/ or edema/swelling). In Kalanithi et al. (2012), 1,455 MO patients demonstrated increases in the cost and incidence of AE out of 84,607 patients undergoing four types of spine fusions (i.e. anterior or posterior cervical fusion, anterior lumbar interbody fusion (ALIF) and posterior lumbar interbody fusion (PLIF) from California 2003-2007 (CASID) Healthcare Cost and Utilization Project’s California State Inpatient Databases).[ 10 ] The MO patients demonstrated a 97% greater in-hospital complication rate (13.6% vs. 6.9% outpatient), a higher mortality rate, higher average hospital costs, and longer lengths of stay (LOS). Evaluating a NSQUIP database of 51,149 patients in 2020, Ottesen et al. found that both under and overweight (MO) patients were at higher risk following anterior cervical surgery for adverse perioperative events (i.e. 30-day AE, readmissions, postoperative infections and mortality from 2005-2016).[ 16 ] Qi et al. (2020) observed that obesity increased the incidence of AE for 156 obese patients (2010-2016) undergoing multilevel ACDF for cervical spondylotic myelopathy (CSM).[ 19 ] Major risk factors included; larger neck circumference, shorter neck length, higher BMI, longer surgical times, greater estimated blood loss, more multilevel disease, and greater severity of CSM.

As National Inpatient Survey (NIS) Databases Showed Increased Risks for Obese Patients Undergoing ACDF Surgery, These Should Be Performed as Inpatients/InHospitals

Two NIS studies documented that obesity increased the frequencies of adverse events following ACDF surgery that should, therefore, be performed as inpatients [ Table 1 ].[ 17 , 20 ] Perez-Roman et al. (2021) observed a greater incidence of perioperative morbidity in obese patients undergoing ACDF in the National Inpatient Survey (NIS) 2004-2014 sample of 1,212,475 patients undergoing ACDF; 9.2% were obese, and this number increased from 5.8% in the earlier years to greater than 13.4% at the end of the study period.[ 17 ] Obesity in patients undergoing ACDF increased the rates of; dysphagia, new postoperative neurological deficits, respiratory depression, hematological/hemorrhagic adverse events, pulmonary embolism, and dural tears. The authors concluded that ACDF in obese patients should be performed as inpatients. Also utilizing a NIS database (2006-2010) involving 78,771 patients, Rogerson et al. (2021) identified multiple risk factors, including obesity, that contributed to adverse events/mortality following 1-2 level inpatient ACDF.[ 20 ] Early AE following ACDF were largely attributed to; obesity, renal disease, anemia, myelopathy, bleeding disorders, chronic obstructive pulmonary disease, obstructive sleep apnea, age over 65, and diabetes. The overall morbidity/adverse event (AE) rate was 3.73%, with the medical 3.13% frequency of AE. Here, the authors concluded: “Surgeons should consider these risk factors when deciding to perform ACDF surgery in an outpatient setting.”

Greater Risks for Postoperative Hematomas in MO Patients Undergoing ACDF

In 2020, Epstein reviewed 11 studies looking at the frequency of postoperative hematomas following anterior cervical surgery (i.e. ACDF, ACF, and anterior cervical spine surgery (ACSS)) [ Table 1 ].[ 4 ] A total of 44,030 patients were evaluated; these data included 4 large series and one National Surgical Quality Improvement Program (NSQUIP) database. Risk factors for postoperative hematomas included; morbid obesity, high or low BMI, DISH (Diffuse Idiopathic Skeletal Hyperostosis), OPLL, surgery lasting over 4 hours, heparin, multilevel surgery, preoperative ASA (American Society of Anesthesiologists) scores of >/= 3, prone surgery, smoking, anemia, age over 65, and myelopathy. The study emphasized the need for early diagnosis of postoperative hematomas to limit perioperative/postoperative morbidity and mortality.

Obese Patients Undergoing ACDF Typically Exhibited More Preoperative Comorbidities and Perioperative Adverse Event (AE) Requiring More Non-Routine Discharges

When Koo et al. (2021) looked at discharges for 17,385 patients from the National Inpatient (NIS) sample undergoing ACDF for CSM, they found 3035 (17.4%) were obese (i.e., vs. 14,350 who were not obese) [ Table 1 ].[ 12 ] Obesity was an independent predictor of a 24.2% rate of non-routine discharges vs. a lower 16.6% incidence of non-routine discharges for those without obesity. Further, 43.5% of obese patients had three or more major preoperative comorbidities vs. a lower 28.1% incidence seen in non-obese patients. The greater comorbidities for obese patients likely contributed to their higher 14.3% frequency of AE vs 10.3% for non-obese patients.

MO Patients Undergoing ACDF Required Longer Operations But Without Higher Reoperation/ Readmission Rates, Length of Stay (LOS) or Non-Routine Discharges

Gross et al. (2023) performed a 1-level ACDF study that included 670 patients operated on from 2010 to 2022; 413 (61.6%) patients were non-obese (BMI < 30), 226 (33.7%) were obese (BMI 30-39.9), while 31(4.6%) were MO (BMI >/= 40) [ Table 1 ].[ 6 ] MO and obese patients undergoing ACDF required longer surgical procedures, but had no increased reoperation/readmission rates, length of stay (LOS), or non routine discharges compared with non-obese patients.

General Impact of Bariatric Surgery on Spine Operations

In 2017, Epstein specifically looked at the increased risks for MO patients (i.e. Classes II and III) with prior histories of bariatric bypasses undergoing different spine operations [ Table 1 ].[ 2 ] Within two years of BS surgery, spine patients exhibited vitamin D deficiency and significant losses in bone mineral density (BMD), which predisposed them to higher risks of spine/other fractures.

Utilizing PearlDiver Databases, Two Studies Showed Preoperative Bariatric Surgery (BS) Reduced AE/Morbidity/Mortality Rates for MO Patients Undergoing ACDF

Utilizing the PearlDiver Database, two studies showed that performing bariatric surgery in MO patients prior to ACDF decreased their postoperative AE/morbidity/mortality rates [ Table 1 ].[ 9 , 13 ] With the PearlDiver Database (2007-2013) and 100% Standard Analytic Files (SAF 100), Malik et al., (2021) compared the 90-day postoperative outcomes for 411 MO patients in Group I (BMI >/= 35 kg/M2) who had BS surgery within two years of ACDF vs. Group 2 patients (BMI >/= 35 kg/M2) undergoing ACDF without prior BS surgery.[ 13 ] MO patients with prior BS had fewer AE following ACDF (i.e., pulmonary embolism, coronary disease, renal disease, and 90-day readmission rates) vs. MO patients without BS. Similarly, using the PearlDiver Spine Database to analyze 160,166 patients, Joo et al. (2023) also found that BS surgery reduced the incidence of AE following ACDF Surgery (2010-2020).[ 9 ] They compared outcomes for non-obese (control patients) vs. 136 obese patients (i.e. BMI < 35 kg/M2m) vs. 343 MO patients (i.e. BMI >/= 35.). Those undergoing ACDF without BS and who were still MO had higher 90-day risks of pulmonary embolism, wound dehiscence, hematomas, and reoperation rates. Alternatively, those who had BS surgery and were no longer MO did not have an increased risk for AE/mortality following ACDF. Notably, the authors of both series recommended that MO patients consider undergoing BS surgery prior to ACDF to reduce perioperative/postoperative AE.[ 9 , 13 ]

Higher Risk of Dural Tears (DT) in Obese Patients Undergoing ACDF Excluding OPLL

Using the National Inpatient Sample (NIS 1998-2010) database for 1,261,140 patients undergoing ACDF, excluding those with OPLL, Kapadia et al. (2019) evaluated risk factors contributing to intraoperative DT [ Table 1 ].[ 11 ] Risk factors identified in the 3048 (0.24%) patients sustaining intraoperative DT included; older age (ages 55-69, or above age 70), non-white patients, obesity, cervical spondylotic myelopathy (CSM) (i.e. not discs/radiculopathy), and hypertension, but not diabetes or hyperlipidemia. Notably, DT contributed to longer average LOS (6.0 days vs. 2.1 days without DT). Here, the authors recommended that obese patients with hypertension and obesity be optimized prior to surgery (i.e., with stringent weight loss and better blood pressure control) to help mitigate their incidence of intraoperative DT. They further supported performing these procedures as inpatients/in-hospitals.

Risk for Respiratory Pulmonary Complications (PRC) After ACDF Surgery and Preoperative Optimization Recommendations

Utilizing the (NIS (National Inpatient Sample Database 2016-2018) including 52,575 elective ACDF procedures, Hardman et al. (2022) found 1454 ACDF-related postoperative Respiratory Pulmonary Complications (RPC) [ Table 1 ].[ 8 ] Factors contributing to the RPC rate included; obesity, older age, African American heritage, diabetes, hypertension, and multilevel surgery in urban hospital settings. Additional factors included; abscess angio-edema, laryngeal edema, vocal cord paralysis, dysphonia, pneumonia, and acute respiratory distress syndrome. The authors concluded; “Our study identified modifiable predictors of RPC after elective ACDF (e.g., obesity, diabetes), which can be used to guide preoperative patient optimization.”

Bone Morphogenetic Protein (BMP) Used in Anterior Cervical Spine Surgery Increased AE Rates

Williams et al. (2011) compared the rates of postoperative AE for 55,862 patients undergoing spine fusions; one group of 11,933 patients received BMP (21%), while the remainder did not [ Table 1 ].[ 23 ] The overall incidence of AE was increased to 5.8% by applying BMP vs. 2.4% without BMP. Notably, a higher 2.1% infection rate was seen with BMP vs. a lower 0.4% without. Specifically, the anterior cervical application of BMP significantly increased the AE rates for new/revision operations, but this did not hold true for posterior cervical procedures or thoracolumbar fusions utilizing BMP.

Increased Risks for MO Patients Undergoing 1-2 Level Anterior Cervical Disc Replacement Surgery

Subramanian et al. (2023) looked at risk factors that correlated with early readmissions and non-home postoperative discharges in NSQUIP (National Surgical Quality Improvement Program) patients undergoing 1-2 level anterior cervical disc replacement surgery (CDR) [ Table 1 ].[ 22 ] They compared the impact of 919 MO Class II/III patients (BMI >/= 35) vs. 1238 obese Class I patients (BMI 30-34.9 kg/ M2) vs. 3,130 non-obese patients (BMI 18.5-29.9 kg/M2) for non-home discharges, and readmission rates.[ 22 ] Increased 30-day non-home discharge rates were observed for MO Class II/III (2.1%) patients vs. Class I (0.7%) patients vs. non-obese (0.5%) patients. Additionally, Class II/III MO patients showed higher 30-day readmission rates (2.1%) vs. obese (1.1%) vs. non-obese patients (0.5%).

CONCLUSION

MO patients (i.e. defined as Class II (BMI >/= 35 kg/M2) or Class III (BMI >/= 40 kg/M2) with their accompanying greater comorbidities exhibited higher perioperative/postoperative morbidity/mortality rates following anterior cervical surgery (i.e., predominantly ACDF). Therefore, shouldn’t anterior cervical procedures performed in MO patients be performed as inpatients, within in-hospital settings?

Ethical approval

Institutional Review Board approval is not required.

Declaration of patient consent

Patients’ consent not required as patients’ identities were not disclosed or compromised.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

References

1. Chotai S, Sielatycki JA, Parker SL, Sivaganesan A, Kay HL, Stonko DP. Effect of obesity on cost per quality-adjusted life years gained following anterior cervical discectomy and fusion in elective degenerative pathology. Spine J. 2016. 16: 1342-50

2. Epstein NE. Bariatric bypasses contribute to loss of bone mineral density but reduce axial back pain in morbidly obese patients considering spine surgery. Surg Neurol Int. 2017. 8: 13

3. Epstein NE. More risks and complications for elective spine surgery in morbidly obese patients. Surg Neurol Int. 2017. 8: 66

4. Epstein NE. Frequency, recognition, and management of postoperative hematomas following anterior cervical spine surgery: A review. Surg Neurol Int. 2020. 11: 356

5. Garringer SM, Sasso RC. Safety of anterior cervical discectomy and fusion performed as outpatient surgery. Spinal Disord Tech. 2010. 23: 439-43

6. Gross EG, Laskay NM, Mooney J, McLeod MC, Atchley TJ, Estevez-Ordonez D. Morbid obesity increases length of surgery in elective anterior cervical discectomy and fusion procedures but not readmission or reoperation rates: A cohort study. World Neurosurg. 2023. 173: e830-7

7. Hans P, Delleuze PP, Born JD, Bonhomme VJ. Epidural hematoma after cervical spine surgery. Neurosurg Anesthesiol. 2003. 15: 282-5

8. Hardman M, Bhandarkar AR, Jarrah RM, Bydon M. Predictors of airway, respiratory, and pulmonary complications following elective anterior cervical discectomy and fusion. Clin Neurol Neurosurg. 2022. 217: 107245

9. Joo PY, Zhu JR, Rilhelm C, Tang K, Day W, Moran J. Anterior cervical discectomy and fusion outcomes in patients with and without bariatric surgery-weight loss does make a difference. Spine (Phila Pa 1976). 2023. 48: 400-6

10. Kalanithi P, Arrigo R, Boakye M. Morbid obesity increases cost and complication rates in spinal arthrodesis. Spine (Phila Pa 1976). 2012. 37: 982-8

11. Kapadia BH, Decker SI, Boylan MR, Shah NV, Paulino CB. Risk factors for cerebrospinal fluid leak following anterior cervical discectomy and fusion. Clin Spine Surg. 2019. 32: E86-90

12. Koo AB, Elsamadicy AA, Sarkozy M, David WB, Reeves BC, Hong CS. Independent association of obesity and nonroutine discharge disposition after elective anterior cervical discectomy and fusion for cervical spondylotic myelopathy. World Neurosurg. 2021. 151: e950-60

13. Malik AT, Noria S, Xu W, Retchin S, Yu ES, Khan SN. Bariatric surgery before elective anterior cervical discectomy and fusion (ACDF) in obese patients is associated with reduced risk of 90-day postoperative complications and readmissions. Clin Spine Surg. 2021. 34: 171-5

14. Martin CT, D’Oro A, Buser Z, Youssef JA, Park JB, Meisel HJ. Trends and costs of anterior cervical discectomy and fusion: A comparison of inpatient and outpatient procedures. Iowa Orthop J. 2018. 38: 167-76

15. Miao W, Ma X, Liang D, Sun Y. Treatment of hematomas after anterior cervical spine surgery: A retrospective study of 15 cases. Neurochirurgie. 2018. 64: 166-70

16. Ottesen TD, Malpani R, Galivanche AR, Zogg CK, Varthi AG, Grauer JN. Underweight patients are at just as much risk as super morbidly obese patients when undergoing anterior cervical spine surgery. Spine J. 2020. 20: 1085-95

17. Perez-Roman RJ, McCarthy D, Luther EM, Lugo-Pico JG, Leon-Correa R, Gaztanaga W. Effects of body mass index on perioperative outcomes in patients undergoing anterior cervical discectomy and fusion surgery. Neurospine. 2021. 18: 79-86

18. Protzman NM, Kapun J, Wagener C. Thoracic spinal subdural hematoma complicating anterior cervical discectomy and fusion: Case report. J Neurosurg Spine. 2016. 24: 295-9

19. Qi M, Xu C, Cao P, Tian Y, Chen H, Liu Y. Does obesity affect outcomes of multilevel ACDF as a treatment for multilevel cervical spondylosis?: A retrospective study. Clin Spine Surg. 2020. 33: E460-5

20. Rogerson A, Aidlen J, Mason A, Pierce A, Tybor D, Salzler MJ. Predictors of inpatient morbidity and mortality after 1-and 2-level anterior cervical diskectomy and fusion based on the national inpatient sample database from 2006 through 2010. Orthopedics. 2021. 44: e675-81

21. Schroeder GD, Hilibrand AS, Arnold PM, Rish DE, Wang JC, Gum JL. Epidural hematoma following cervical spine surgery. Global Spine J. 2017. 7: 120S-6

22. Subramanian T, Shinn D, Shahi P, Akosman I, Amen T, Maayan O. Severe obesity is an independent risk factor of early readmission and nonhome discharge after cervical disc replacement. Neurospine. 2023. 20: 890-8

23. Williams BJ, Smith JS, Fu KM, Hamilton DK, Polly DW, Ames CP. Does bone morphogenetic protein increase the incidence of perioperative complications in spinal fusion? A comparison of 55,862 cases of spinal fusion with and without bone morphogenetic protein. Spine (Phila Pa 1976). 2011. 36: 1685-91

24. Yerneni K, Burke JF, Chunduru P, Molinaro AM, Riew KD, Traynelis VC. Safety of outpatient anterior cervical discectomy and fusion: A systematic review and meta-analysis. Neurosurgery. 2020. 86: 30-45