Impact of Severe Obesity on Outcomes in Single-Level Anterior Cervical Discectomy and Fusion (ACDF): A Large-Scale Comparative Study

Abstract

Background: Anterior cervical discectomy and fusion (ACDF) is a common procedure for cervical radiculopathy and myelopathy. Severe obesity (BMI ≥ 40 or BMI ≥ 35 with comorbidities) is associated with increased perioperative risks. This study examines the impact of severe obesity on outcomes in patients undergoing single-level ACDF. Methods: Data from the Nationwide Inpatient Sample (2016–2019) were analyzed, including 85,585 patients who underwent single-level ACDF. Patients were classified as severely obese (n = 4935) or non-obese (n = 80,650). Outcomes such as length of stay, complications, and in-hospital mortality were compared using SPSS and MATLAB, with a significance level of p < 0.05. Results: Severely obese patients were younger (54 vs. 55.7 years, p < 0.001) and had more comorbidities like type 2 diabetes (38% vs. 17.8%, p < 0.001) and obstructive sleep apnea (31.1% vs. 9.5%, p < 0.001). They experienced longer hospital stays (1.92 vs. 1.65 days, p < 0.001) but similar in-hospital mortality (0.1%, p = 0.506). Severe obesity was linked to higher odds of complications, including increased risks of dehiscence (OR 8.2), respiratory failure (OR 6.5), myocardial infarction (OR 5.5), Horner syndrome (OR 4.7), pulmonary edema (OR 4.5), and dural tears (OR 4.1). Risks of acute kidney injury, pulmonary embolism, and dysphonia were also elevated in severely obese patients. Conclusion: Severe obesity is associated with higher complication rates and longer hospital stays following ACDF. Tailored perioperative management is essential to mitigate these risks and improve outcomes in this high-risk population.

1. Introduction

Anterior cervical discectomy and fusion (ACDF) remains the definitive treatment for cervical radiculopathy and myelopathy, particularly in patients with cervical spondylosis [1,2,3]. With the global population aging rapidly, the incidence of spondylosis—and the corresponding need for ACDF—is expected to surge. ACDF is primarily indicated when conservative management fails to alleviate symptoms in degenerative cervical spine disorders, including spondylosis, disk herniations, fractures, and spinal tumors. Its high efficacy and favorable safety profile have cemented it as one of the most frequently performed procedures in addressing cervical spine degeneration.

Body mass index (BMI) is a well-established risk factor for increased complications and suboptimal outcomes after ACDF [4,5]. Patients with elevated BMI, coupled with characteristics such as larger neck circumference and shorter neck length, are prone to longer operative times, greater blood loss, and a heightened likelihood of postoperative complications [6]. These anatomical and physiological challenges further complicate the procedure, impacting both intraoperative management and postoperative recovery. In patients with severe obesity, however, ACDF poses specific challenges. The increased subcutaneous fat deposition and broader anatomical corridors introduce greater complexity in accessing the cervical spine. This often necessitates more forceful and prolonged retraction of adjacent structures such as the longus colli muscles, esophagus, and trachea, which can elevate the risk of complications. These include localized edema, tissue ischemia, longer operative durations, and increased intraoperative blood loss.

Obesity has been consistently associated with higher rates of perioperative complications and poorer outcomes in surgical procedures, including ACDF [7,8,9,10]. According to the WHO, obesity is categorized by a BMI of ≥30.0, with further classifications as class I (30.0–34.9), class II (35.0–39.9), and class III (≥40.0). The prevalence of obesity in the United States continues to rise, placing this population at a significantly greater risk of developing degenerative spinal disorders across all levels of the spine, in comparison to individuals with a healthy BMI [11]. Patients with a BMI over 30 have been identified as being at a heightened risk for developing complications such as dysphagia, neurological issues, respiratory complications, hematologic disorders, pulmonary embolism (PE), and durotomy.

A deeper insight into the impact of obesity on inpatient complications after ACDF could enhance patient selection, preoperative risk stratification, and patient counseling, potentially mitigating avoidable perioperative complications. This study seeks to evaluate the prevalence of obesity among ACDF patients and to assess its influence on postoperative inpatient outcomes, with the goal of improving clinical management strategies for this high-risk population.

Research Question

Our goal is to investigate the correlation between severe obesity (BMI ≥ 40 or BMI ≥ 35 with obesity-related comorbidities) and the outcomes of patients undergoing single-level ACDF.

2. Methods

2.1. Research Dataset

This study utilized a comprehensive dataset extracted from the Nationwide Inpatient Sample (NIS), the largest publicly available all-payer inpatient care database in the United States. The dataset included a total of 85,585 patients who underwent single-level anterior cervical discectomy and fusion (ACDF) between 2016 and 2019.

2.2. Study Period and Data Source

The study period spanned from 1 January 2016 to 31 December 2019. The NIS, a core component of the Healthcare Cost and Utilization Project (HCUP), captures 20% of inpatient stays from HCUP-associated hospitals, amounting to approximately seven million unweighted enrollments annually.

2.3. Patient Identification and Obesity Definition

Patients undergoing single-level ACDF were identified using specific ICD-10 codes. Severe obesity was defined by the ICD-10 code E66.01, indicating patients with a body mass index (BMI) of 40 or higher or a BMI of 35 or higher with obesity-related health conditions (e.g., diabetes, hypertension). In total, 4935 patients were identified as having severe obesity, while 80,650 patients were classified as non-severe or non-obese.

2.4. Statistical Analyses

Statistical analyses were performed using SPSS 26 and MATLAB 2024. Crosstabs and independent sample t-tests were conducted to compare outcomes between severely obese and non-obese patients undergoing single-level ACDF. A significance level of p < 0.05 was applied.

2.5. Comorbidity and Outcome Identification

Comorbidities were identified using ICD-10 codes and included conditions such as diabetes, hypertension, and chronic respiratory disease. Clinical outcomes were also extracted using ICD-10 codes and included in-hospital mortality, length of stay, complications, and overall hospitalization costs. Complications analyzed included dysphagia, blood loss anemia, cervical spinal cord injury, urinary tract infection (UTI), acute renal failure, pneumonia, blood transfusion requirement, venous thromboembolism, pulmonary edema, ileus, sepsis, and pulmonary embolism.

2.6. Ethical Considerations

The study was conducted under exempt status granted by the institutional review board due to the de-identified nature of the data. No informed consent was required.

3. Results

3.1. Comparison of Key Demographic and Hospital Characteristics

Table 1. Demographic and hospital characteristics of patients undergoing single-level ACDF surgery stratified by severe obesity status.

Parameter	Without Severe Obesity (%)	Severe Obesity (%)	Significance
Total surgeries	80,650	4935	-
Average age (y)	55.7	54	p < 0.001
Female (%)	51.3	57.1	p < 0.001
Primary expected payer—Medicare (%)	33.8	35	p < 0.001
Primary expected payer—Medicaid (%)	10.6	12.2
Primary expected payer—private, including HMO (%)	44.5	44.8
Primary expected payer—self-pay (%)	1.2	1.1
Primary expected payer—no charge (%)	0.1	0.1
Primary expected payer—other (%)	9.8	6.9
Status of hospital (STRATA)—rural (%)	72.9	75.6	p < 0.001
Status of hospital (STRATA)—urban nonteaching (%)	23.3	20.7
Status of hospital (STRATA)—urban teaching (%)	3.8	3.7

presents the demographic and hospital characteristics of patients undergoing single-level ACDF surgery, comparing those with and without severe obesity.

Severely obese patients were younger (54 vs. 55.7 years, p < 0.001) and had a higher percentage of females (57.1% vs. 51.3%, p < 0.001). Medicare coverage was more common among severely obese patients (35% vs. 33.8%, p < 0.001). A greater proportion of surgeries for severely obese patients occurred in rural hospitals (75.6% vs. 72.9%, p < 0.001).

3.2. Comparison of Comorbidities Between Severely Obese and Non-Obese Patients

Table 2. Comorbidities in patients undergoing single-level ACDF surgery by severe obesity status.

Prameter	Without Severe Obesity (%)	Severe Obesity (%)	Significance
Type 2 Diabetes Mellitus	17.8	38	p < 0.001
Diabetes Mellitus	19.5	38.5	p < 0.001
Mental Disorders	40.4	45.7	p < 0.001
Hypertension	56.3	43.7	p < 0.001
Dyslipidemia	70	30	p < 0.001
Obstructive Sleep Apnea	9.5	31.1	p < 0.001
Chronic Kidney Disease	3.6	6.4	p < 0.001
Chronic Lung Disease	7.8	11.4	p < 0.001
Thyroid Disorder	11.7	15.4	p < 0.001
Chronic Anemia	2.3	3.5	p < 0.001
Heart Failure	0.1	0.3	p < 0.001
Connective Tissue Disorder	0.1	0.1	p = 0.621
History of Myocardial Infarction	2.9	3.1	p = 0.372
Peripheral Vascular Disease	1.3	1.4	p = 0.559
Dementia	0.2	0.2	p = 0.002
Peptic Ulcer Disease	0.3	0.3	p = 0.623
IBD (Inflammatory Bowel Disease)	0.5	0.3	p = 0.038
Hemiplegia	0.2	0.1	p = 0.085
Neoplasms	0.8	0.9	p = 0.576
Neoplasms of Lymphoid/Hematopoietic	0.3	0.3	p = 0.664
Fibromyalgia	3.8	4.4	p = 0.041
Smoking	1.2	0.7	p = 0.001
Alcohol Abuse	1.2	1	p = 0.279
Osteoporosis	2.3	2	p = 0.137
Parkinson Disease	0.5	0.3	p = 0.103
Alzheimer Disease	0.1	0.1	p = 0.097

shows the comorbidities associated with patients undergoing single-level ACDF surgery, comparing those with and without severe obesity. Severely obese patients were significantly more likely to have type 2 diabetes mellitus (38% vs. 17.8%, p < 0.001), obstructive sleep apnea (31.1% vs. 9.5%, p < 0.001), and chronic kidney disease (6.4% vs. 3.6%, p < 0.001). They also had a higher prevalence of mental disorders (45.7% vs. 40.4%, p < 0.001) and thyroid disorders (15.4% vs. 11.7%, p < 0.001). However, they were less likely to have hypertension (43.7% vs. 56.3%, p < 0.001) and dyslipidemia (30% vs. 70%, p < 0.001). Other notable differences include higher rates of chronic lung disease (11.4% vs. 7.8%, p < 0.001) and chronic anemia (3.5% vs. 2.3%, p < 0.001) in severely obese patients.

3.3. Comparison of Hospitalization Outcomes Between Severely Obese and Non-Obese Patients

Table 3. Hospitalization outcomes for single-level ACDF surgery by severe obesity status.

Parameter	Without Severe Obesity (%)	Severe Obesity (%)	Significance
Died during hospitalization (%)	0.1	0.1	p = 0.506
Length of stay (Days)	1.65	1.92	p < 0.001
Total charges (USD)	66,913	66,655	p = 0.702

shows the hospitalization outcomes for patients undergoing single-level ACDF surgery. There was no significant difference in in-hospital mortality between severely obese and non-obese patients (both 0.1%, p = 0.506). However, the length of stay was significantly longer for severely obese patients (1.92 days vs. 1.65 days, p < 0.001). Total hospital charges were similar between the two groups, with no significant difference (USD 66,655 vs. USD 66,913, p = 0.702).

3.4. Postoperative Complications in Severely Obese vs. Non-Obese Patients

Table 4. Postoperative complications with no significant difference between severe and non-severe obesity groups following single-level ACDF surgery.

Parameter	Without Severe Obesity (%)	Severe Obesity (%)	Significance
Venous Thromboembolism	0.1	0.1	p = 0.452
Cardiac Arrhythmias	2	2.3	p = 0.092
Pneumonia	0.2	0.3	p = 0.446
Urinary Tract Infection (UTI)	0.6	0.8	p = 0.059
Blood Transfusion	0.2	0.1	p = 0.347
Blood Loss Anemia	1.6	1.6	p = 0.907
Dysphagia	5.1	4.9	p = 0.383
Brachial Plexus Injury	0	0	p = 0.338
Cerebrospinal Fluid Leak	0.3	0.2	p = 0.483

highlights the postoperative complications that did not differ significantly between severely obese and non-obese patients undergoing single-level ACDF surgery. The rates of venous thromboembolism (0.1% vs. 0.1%, p = 0.452), pneumonia (0.3% vs. 0.2%, p = 0.446), and dysphagia (4.9% vs. 5.1%, p = 0.383) were similar between the two groups. Other complications such as cardiac arrhythmias, urinary tract infections, and cerebrospinal fluid leaks also showed no statistically significant differences.

3.5. Postoperative Complications with Significantly Higher Odds in Severely Obese Patients

Figure 1 presents the odds ratios (ORs) and confidence intervals (CIs) for various postoperative complications in severely obese patients after single-level ACDF surgery. The OR provides a measure of the likelihood that a complication occurs in severely obese patients compared to non-obese patients. An OR greater than 1 indicates a higher risk of complication in the severely obese group.

• Dehiscence had the highest OR at 8.2 (95% CI: 2.8–23.9, p < 0.001).
• Respiratory failure had an OR of 6.5 (95% CI: 3.1–13.6, p < 0.001), showing a significantly increased risk for severely obese patients.
• Myocardial infarction had an OR of 5.5 (95% CI: 2.0–15.0, p < 0.001), indicating a markedly higher risk in the severely obese group.
• Horner syndrome had an OR of 4.7 (95% CI: 2.3–9.5, p < 0.001).
• Pulmonary edema had an OR of 4.5 (95% CI: 2.5–7.9, p < 0.001).
• Dural tear had an OR of 4.1 (95% CI: 2.0–8.2, p < 0.001).
• Acute kidney injury had an OR of 2.6 (95% CI: 2.0–3.3, p < 0.001).
• Pulmonary embolism had an OR of 2.5 (95% CI: 1.3–4.9, p = 0.005).
• Dysphonia had an OR of 2.2 (95% CI: 1.6–3.1, p < 0.001).

These findings indicate that severely obese patients are at significantly higher risk for multiple complications following single-level ACDF surgery compared to non-obese patients.

4. Discussion

ACDF is the most commonly performed procedure on the cervical spine, with its incidence tripling over the past two decades. Despite its reputation as a safe and effective intervention, ACDF is not without risks, and significant complications can still arise [1,2,12,13,14,15,16]. Advances in surgical techniques and innovations in interbody fusion devices and plating systems have contributed to reducing postoperative morbidity. However, surgeons must remain vigilant, recognizing potential complications, fully informing patients of the associated risks, and implementing appropriate management strategies. ACDF remains the gold standard for addressing cervical radiculopathy and myelopathy, particularly when dealing with focal anterior compression of the nerve roots and/or spinal cord, often caused by cervical spondylosis.

4.1. Unique Contributions of This Study

Unlike prior studies, this research provides a detailed quantification of specific risks associated with severe obesity, such as respiratory failure (OR 6.5), myocardial infarction (OR 5.5), and wound dehiscence (OR 8.2). These findings underscore the disproportionate impact of obesity-related anatomical and physiological challenges on perioperative outcomes. Notably, our study introduces a novel perspective by addressing geographical disparities, highlighting the higher prevalence of severe obesity in rural hospital settings (75.6% vs. 72.9%) [17,18,19,20]. This geographical insight emphasizes the need for targeted resource allocation and tailored interventions in these populations. While prior research has examined general risks associated with obesity, this study uniquely quantifies these risks within a large, nationally representative cohort, providing actionable insights for clinical and policy-level decision-making [1,4,12,21,22].

4.2. Practical Implications for Clinical Practice

The markedly higher odds of complications in severely obese patients underscore the critical need for tailored preoperative risk stratification and perioperative management strategies. For instance, enhanced preoperative respiratory evaluations for conditions like obstructive sleep apnea could mitigate risks of respiratory failure. Similarly, optimizing preoperative cardiovascular status could reduce the likelihood of myocardial infarction. Surgical teams in rural hospitals, where the prevalence of severe obesity is higher, may benefit from additional training [2] and resource support to address the unique challenges posed by this population. These actionable recommendations could improve outcomes and reduce complications, particularly in resource-limited settings.

4.3. Study Findings: Demographics

Severely obese patients were generally younger and more likely to be female compared to non-obese patients. Interestingly, a larger proportion of surgeries for severely obese patients were performed in rural hospitals. This finding could reflect a geographic disparity in the distribution of obesity or surgical access in certain populations. Other studies, such as those by Roberto et al. [2], have similarly observed a higher prevalence of female patients among obese individuals, particularly those from lower socioeconomic backgrounds. These demographic differences suggest that gender, socioeconomic status, and geographic location may influence surgical outcomes differently across populations.

4.4. Study Findings: Comorbidities

Severely obese patients in our study exhibited higher rates of significant comorbidities, including type 2 diabetes, obstructive sleep apnea, chronic kidney disease, and mental health disorders. However, we found surprisingly lower rates of hypertension and dyslipidemia in this population. The increased prevalence of conditions like diabetes and sleep apnea in severely obese patients aligns with findings from previous studies, which have linked higher BMI with a greater burden of metabolic and respiratory disorders [1,2]. The presence of these comorbidities can complicate both the surgical procedure and the postoperative recovery process, underscoring the importance of thorough preoperative assessment and planning.

4.5. Study Findings: Postoperative Complications

Severely obese patients were found to have significantly longer hospital stays compared to non-obese patients (1.92 days vs. 1.65 days), reflecting more complex postoperative courses. However, no significant differences were observed in in-hospital mortality rates or total hospital costs between the two groups. Interestingly, while conditions like venous thromboembolism, pneumonia, and dysphagia showed similar rates across BMI categories, severely obese patients had a markedly higher risk of certain serious complications, including wound dehiscence, respiratory failure, myocardial infarction, Horner syndrome, and pulmonary edema. In some cases, the odds ratios (ORs) indicated up to an 8-fold increased risk for these complications.

These findings emphasize the need for increased vigilance and tailored preoperative strategies for severely obese patients. It is essential to implement a multidisciplinary approach, involving anesthesiologists, nutritionists, and physical therapists, to optimize patient outcomes and mitigate the risks associated with obesity.

4.6. Clinical Implications of Increased Complication Risks in Severely Obese Patients

The clinical significance of these findings is profound, particularly when considering the implications for surgical decision-making and patient outcomes. The markedly higher odds of severe complications, such as respiratory failure, myocardial infarction, and wound dehiscence in severely obese patients, underscore the need for heightened preoperative risk assessment and tailored perioperative care [4,7]. Surgeons must carefully weigh the benefits of ACDF against these elevated risks, particularly in patients with severe obesity, who may require additional resources and more complex postoperative management [4,7,11]. The increased risk of complications not only impacts immediate surgical outcomes but may also prolong recovery and increase the likelihood of rehospitalization, further straining healthcare resources. These findings highlight the importance of a multidisciplinary approach to the surgical care of obese patients, which includes early identification of at-risk individuals, optimization of comorbidities, and enhanced postoperative monitoring to improve outcomes and mitigate potential complications.

4.7. Tailored Perioperative Management for Severely Obese Patients

Given the increased risk of complications in severely obese patients, individualized perioperative management is critical for improving outcomes. A multidisciplinary approach, involving anesthesiologists, nutritionists, and physical therapists, can help optimize patient care both before and after surgery [4,12]. Tailoring care to address specific comorbidities, such as diabetes and obstructive sleep apnea, and implementing strategies for better postoperative monitoring are essential to mitigate risks. This personalized management can reduce the likelihood of adverse events and enhance recovery in this high-risk population.

4.8. Broader Implications for Policy and Research

The findings of this study have significant implications for both clinical practice and healthcare policy. The identification of geographical disparities in the prevalence of severe obesity highlights the need for targeted investments in rural healthcare infrastructure. Policymakers could allocate additional resources to rural hospitals, enabling them to better manage the complex needs of severely obese patients undergoing ACDF. Furthermore, our results advocate for the development of standardized preoperative protocols that incorporate obesity-specific risk factors, ensuring that high-risk patients receive optimal care across diverse healthcare settings. Future research should focus on validating these findings in prospective cohorts and exploring novel interventions to mitigate the identified risks.

4.9. Limitations

While our study provides valuable insights, several limitations should be acknowledged. First, the absence of intraoperative data, such as surgical time, blood loss, or specific techniques used, limits the ability to directly link the observed complications to procedural factors. Second, the lack of long-term outcomes, including functional recovery, quality of life, or patient satisfaction, restricts the scope of our findings to the immediate postoperative period. Future studies should integrate patient-reported outcomes and long-term follow-up to better understand the comprehensive impact of severe obesity on ACDF outcomes. Third, the retrospective nature of this study and reliance on administrative coding may introduce potential inaccuracies or under-reporting of complications. Lastly, the absence of detailed data on regional healthcare access and socioeconomic factors limits our ability to fully explore the drivers of geographical disparities. Addressing these gaps in future research could provide a more holistic understanding of the interplay between obesity, surgical outcomes, and healthcare disparities.

5. Conclusions

Severely obese patients were younger, predominantly female, and had higher rates of comorbidities, such as type 2 diabetes and sleep apnea. They also faced increased risks of complications like respiratory failure and myocardial infarction, though hospital costs remained similar to non-obese patients. This study’s limitations include a reliance on retrospective coding and lack of patient-reported outcomes. Despite this, it offers important insights into managing high-risk ACDF patients.