Abstract
Objective Including conditions like obesity, diabetes, hypertension, and dyslipidemia, metabolic syndrome disrupts metabolic homeostasis and impairs recovery, increasing the risk of surgical complications. This study evaluates the impact of metabolic syndrome on spine surgery outcomes, addressing inconsistencies in the existing literature.
Methods Four databases were searched until December 2024 for studies comparing the postoperative complication rates of spine surgeries between patients with and without metabolic syndrome. Following deduplication, 2 authors independently reviewed the studies. For each included study, demographics and incidence rates of postoperative complications were extracted separately by 2 authors. Data analysis was performed using R.
Results After deduplication, 115 studies were evaluated for inclusion in our study. Following the review of full texts, 11 studies were included. No significant differences were found between patients with and without metabolic syndrome in terms of mortality and nonhome discharge, pulmonary thromboendarterectomy, pneumonia, and sepsis (P > 0.05). However, metabolic syndrome was associated with a significantly increased risk of 30-day readmission (RR: 1.5, 95% CI: 1.2–1.8), reoperation (RR: 1.3, 95% CI: 1.1–1.6), cardiac complications (RR: 1.7, 95% CI: 1.5–2.1), respiratory complications (RR: 1.68, 95% CI: 1.17–2.40), cerebrovascular complications (RR: 2.0, 95% CI: 1.4–2.9), renal complications (RR: 4.48, 95% CI: 2.58–7.80), urinary complications (RR: 1.45, 95% CI: 1.41–1.48), venous thromboembolism (RR: 1.3, 95% CI: 1.1–1.6), and wound complications (RR: 1.6, 95% CI: 1.3–1.9).
Conclusions Metabolic syndrome might significantly increase the risk of some postoperative complications in spine surgery patients. These findings highlight the need for personalized preoperative planning and management strategies to mitigate surgery risks.
Clinical Relevance Identifying and optimizing metabolic syndrome components before surgery may improve patient outcomes and reduce complication rates.
Level of Evidence 2.
Introduction
Metabolic syndrome (MetS) is a state of hormonal dysfunction that can increase the risk of cardiovascular mortality and various chronic diseases.1 The core components of MetS definitions include having a body mass index (BMI) >30th kg/m2, diabetes mellitus, hypertension (HTN), and dyslipidemia (DL).2,3 Factors such as genetic predisposition, old age, smoking, and sedentary lifestyle increase the risk of MetS.4 With a global prevalence of 45.1%, MetS has a substantial burden on public health systems due to its association with both chronic diseases and surgical complications.2,5,6
Previous studies have shown that MetS is associated with a higher risk of osteoarthritis, proposing a connection in their pathophysiology, possibly involving inflammation, oxidative stress, and metabolic homeostasis imbalance.7–9 MetS has been consistently linked to poorer surgery outcomes and more preoperative complications in various surgeries, including but not limited to cardiovascular and orthopedic procedures.1 ,0 The metabolic abnormalities in MetS appear to interfere with the body’s ability to heal and recover from surgical stress, leading to more extended hospital stays, increased postoperative infections, delayed recovery, higher rates of postoperative complications and mortality, and higher health care costs.1 ,0–12
Approximately 900,000 spine surgeries are performed annually on American adults.13 These surgeries are becoming increasingly common as the population grows older, and degenerative spine disorders are more prevalent in the elderly.14 While there is limited literature on the specific effects of MetS on spinal surgeries, some studies suggest that MetS significantly increases the risk of complications, length of hospital stays, and hospital readmissions.4,15–17 However, some studies did not find MetS to be an independent predictor for spinal surgery outcomes, and some found different results regarding different complications.15,16,18,19
Given the growing prevalence of MetS and the rising number of spinal surgeries, understanding the impact of MetS on surgical outcomes is crucial for risk stratification and improved patient care strategies. In this systematic review and meta-analysis, we aim to integrate existing evidence on the impact of MetS on outcomes for patients following spine surgery, addressing inconsistencies in the present literature.
Methods
Search Strategy and Databases
Studies were retrieved through a systematic search in PubMed, Embase, Scopus, and Web of Science without restrictions from inception to December 2024. The detailed search string is available in Table S1. The reference list of the studies that were obtained has been examined to identify additional related research. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework has been utilized to present the findings. The study protocol was registered with PROSPERO, and the registration ID CRD 42024606549 was assigned.
Eligibility Criteria
Studies that assessed the impact of MetS on the spine surgery outcome were included in the study, and the inclusion criteria were as follows: (1) studies on patients undergoing spine surgery; (2) diagnosis of MetS based on the following criteria having at least 2 of related conditions (BMI >30, diabetes mellitus, HTN, and DL) in at least 1 group of patients; (3) inclusion of a comparison group of patients without MetS; (4) reporting on at least 1 postoperative outcome, including complications (eg, infections, cardiovascular, pulmonary, or neurological), length of hospital stay, 30-day readmissions or reoperations, mortality, or functional recovery; and (5) articles published in English in peer-reviewed journals. Exclusion criteria included (1) studies focusing on pediatric or nonhuman subjects; (2) reviews, editorials, conference abstracts, or case reports lacking sufficient quantitative data; (3) studies without separate outcome data for patients with and without MetS; (4) studies not assessing postoperative outcomes specific to spine surgery; and (5) articles with incomplete or nonretrievable data.
Study Selection
All records identified through database searches were imported into reference management software, and duplicates were removed. In the first stage, 2 reviewers (F.S. and M.T.P.F.) independently screened titles and abstracts to exclude irrelevant studies. In the next step, full texts of potentially eligible studies were retrieved and assessed for inclusion. Any disagreements between the reviewers were resolved through discussion or consultation with a third reviewer (A.S.K.).
Data Extraction
Data extraction was performed independently by 2 reviewers (F.S. and M.T.P.F.) using a standardized form, capturing study characteristics (author, year, design, and data source), population details (sample size, MetS prevalence, and gender distribution), surgical procedures (eg, spinal fusions), MetS definitions (criteria such as diabetes, HTN, BMI ≥ 30, and DL), reported outcomes (eg, complications, mortality, readmissions, reoperations, and length of stay), and follow-up duration. Discrepancies were resolved through discussion or a third reviewer (A.S.K.). Data were organized into structured tables for consistency.
Quality Assessment
The methodological quality of the included studies was assessed using the Newcastle–Ottawa Scale for cohort studies.20 Each study was evaluated across 3 domains: selection of participants (4 points), comparability of groups (2 points), and ascertainment of outcomes (3 points), for a total possible score of 9. Studies scoring 7 or above were considered high quality. Quality assessment was performed independently by 2 reviewers, with discrepancies resolved through consensus.
Statistical Analysis
Risk ratios (RRs) and standard mean differences were calculated for binary and continuous outcomes, respectively, with 95% CIs. A random-effects model was used for meta-analysis to account for heterogeneity. Cochran’s Q test was employed to evaluate heterogeneity, with a P value of 0.10 indicating the presence of heterogeneity. Statistical heterogeneity was assessed using the I 2 statistic, with a threshold of 60% prompting further analysis for heterogeneity and outlier detection. Sensitivity analyses were performed by excluding individual studies to evaluate the robustness of the results. Publication bias was assessed visually using funnel plots and statistically using Egger’s regression test. All analyses were conducted at a significance level of 0.05. A meta-analysis was conducted using R software (version 4.4.0), employing the R packages meta and dmetar.
Results
Study Selection and Characteristics
According to our primary search in 4 databases (PubMed, Web of Science, Embase, and Scopus), a total of 115 studies were identified. Following the removal of duplicates and title and abstract screening, 16 studies were subjected to full-text screening. Finally, according to the inclusion and exclusion criteria, 11 studies1,4,15–23 comprising 3,214,284 spine surgery cases (599,108 MetS patients and 2,615,176 non-MetS patients) were deemed eligible for inclusion in our meta-analysis. Figure 1 illustrates the PRISMA flowchart for study selection.
Preferred Reporting Items for Systematic Reviews and Meta-Analyses flowchart.
All the included studies were retrospective cohorts and were published between 2012 and 2024. These studies investigated patients undergoing spine surgery utilizing data from the National Inpatient Sample (NIS)17,21 and the American College of Surgeons National Surgical Quality Improvement Program (NSQIP),1,4,16,18,19,23 as well as single-center data registries from US hospitals.15,20,22 Seven studies reported the outcome through a 30-day follow-up,1,4,16,18–20,23 while 2 studies reported the results of a 1-year follow-up.15,22 Memtsoudis et al21 and Naessig et al’s study17 did not mention the follow-up period. Table 1 presents the type of spine surgery investigated in each study and details the characteristics of the included studies.
Baseline characteristics of included studies.
Quality Assessment
The assessment of the methodological quality of each included study was performed using the Newcastle–Ottawa Scale. Two studies obtained a score of 9, and 9 studies obtained 8 points. All studies obtained the full points in the selection and comparability domains. A comprehensive summary of bias risks and their corresponding ratios can be found in Table 2.
The quality assessment according to the Newcastle–Ottawa Scale of each cohort study.
Meta-Analysis
Primary Outcomes
Our meta-analysis demonstrated a comparable mortality incidence rate following spine surgery in MetS cases compared with non-MetS (RR = 1.40, 95% CI = 0.75–2.62, I 2 = 71%, P for heterogeneity = 0.0043; Figure 2A). However, the sensitivity analysis unveiled a significantly higher mortality incidence in MetS patients following the exclusion of the Memtsoudis et al study21 (RR = 1.98, 95% CI = 1.36–2.89, I 2 = 0%; Figure 2B, no outliers detected).
(A) Forest plot of mortality comparison between metabolic syndrome (MetS) and non-MetS patients undergoing spine surgery. (B) Leave-one-out analysis results for mortality outcome.
MetS patients showed significantly higher 30-day readmission rates (RR = 1.51, 95% CI = 1.25–1.82, I 2 = 50%, Figure 3A), which remained consistent after performing a leave-one-out analysis (Figure 3B). MetS cases also demonstrated a significantly higher 30-day reoperation rate (RR = 1.34, 95% CI = 1.08–1.66, I 2 = 39% Figure 4A); however, after conducting sensitivity analysis, it was shown that by excluding Thomas et al’s study,23 there was no significant difference between MetS and non-MetS cases (RR = 1.30, 95% CI = 0.97–1.75, I 2 = 43%; Figure 4B).
(A) Forest plot of 30-day readmission comparison between metabolic syndrome (MetS) and non-MetS patients undergoing spine surgery. (B) Leave-one-out analysis results for 30-day readmission outcome.
(A) Forest plot of 30-day reoperation comparison between metabolic syndrome (MetS) and non-MetS patients undergoing spine surgery. (B) Leave-one-out analysis results for 30-day reoperation outcome.
There was symmetry of the funnel plots for all the primary outcomes (mortality, 30-day readmission, and 30-day reoperation); Figure 5A–C showed minimal publication bias. In Figure 5A, the dashed vertical line represents the common-effect pooled RR (1.15), while the solid vertical line indicates the random-effects pooled RR (1.32). This symmetry was statistically confirmed by Egger’s linear regression test, as there was no indication of significant publication bias in any of the primary outcomes (all P-values > 0.05).
Funnel plots for primary outcomes: (A) mortality, (B) 30-day readmission, and (C) 30-day reoperation.
Secondary Outcomes
Cardiovascular and Neurological Complications
Based on our analysis, it was shown that the incidence of cardiac complications (RR = 1.77, 95% CI = 1.51–2.08, I 2 = 69%, P for heterogeneity = 0.0011, Figure S1, no outliers detected) and cerebrovascular complications (RR = 2.01, 95% CI = 1.41–2.87, I 2 = 37%, Figure S2) is significantly higher in the MetS population compared with non-MetS.
Pulmonary Complications
A notably higher incidence of respiratory complications (RR = 1.68, 95% CI = 1.17–2.40, I 2 = 95%, P for heterogeneity <0.0001, Figure S4, no outliers detected) was illustrated in MetS cases. However, a comparable incidence rate of pneumonia (RR = 1.44, 95% CI = 0.68–3.02, I 2 = 41%, Figure S4) was demonstrated between the 2 populations.
Renal and Urinary
MetS patients undergoing spine surgery showed a significantly higher incidence of urinary complications (RR = 1.44, 95% CI = 1.40–1.48, I 2 = 0%, Figure S5) as well as renal complications (RR = 4.48, 95% CI = 2.58–7.80, I 2 = 46.6%, Figure S6).
Hematological Complications
While the venous thromboembolism (VTE) incidence rate was significantly higher in MetS cases (RR = 1.29, 95% CI = 1.05–1.57, I 2 = 60%, P for heterogeneity =0.014, Figure S7, no outliers detected), there was no significant difference between MetS and non-MetS in terms of pulmonary thromboendarterectomy incidence (RR = 1.44, 95% CI = 0.69–3.03, I 2 = 41%, Figure S8). In addition, transfusion need was comparable between the 2 groups of patients (RR = 1.07, 95% CI = 0.96–1.21, I 2 = 55%, Figure S9).
Wound and Infection-Related Complications
Wound complications were demonstrated to be significantly more prevalent in MetS patients (RR = 1.58, 95% CI = 1.28–1.92, I 2 = 64%, P for heterogeneity = 0.0053, Figure S10). The study by Chung et al was detected as an outlier and thus removed from the analysis (RR = 1.65, 95% CI = 1.49–1.82, I 2 = 28%, P for heterogeneity =0.20). However, there was no significant difference between the 2 populations in terms of sepsis (RR = 1.41, 95% CI = 0.89–2.22, I 2 = 80%, P for heterogeneity <0.0001, Figure S11). The study by Memtsoudis et al was detected as an outlier and thus removed from the analysis (RR = 1.66, 95% CI = 1.36–2.02, I 2 = 0.0%, P for heterogeneity =0.78).
Hospitalization-Related Outcomes
MetS patients show a considerably more extended length of stay (standard mean difference = 0.27, 95% CI = 0.15–0.38, I 2 = 76%, P for heterogeneity = 0.0054; Figure S12; no outliers detected). However, nonhome discharge rate (RR = 1.93, 95% CI = 0.99–3.79, I 2 = 84%, P for heterogeneity = 0.0016; Figure S13; no outliers detected) as well as operation time (RR = 0.04, 95% CI = −0.07 to 0.15, I 2 = 0%, Figure S14) were not significantly different between the 2 groups.
Figure 6 summarizes our meta-analysis results, comparing each outcome’s incidence between MetS and non-MetS patients.
Summary of the meta-analysis results. (A) Categorical outcomes. (B) Continuous outcomes.
Discussion
Our study investigated the potential association between MetS and the incidence risk of medical and surgical complications following spine surgeries, as well as hospitalization-related outcomes. We demonstrated that among patients undergoing spine surgeries, those with MetS have a higher risk of 30-day readmission, 30-day reoperation, cardiac complications, cerebrovascular complications, renal complications, respiratory complications, urinary complications, VTE, and wound complications, as well as a longer length of stay after spine surgeries. However, a comparable risk of mortality, nonhome discharge, pneumonia, pulmonary thromboendarterectomy, sepsis, and transfusion was shown between MetS and control cases.
MetS incidence and prevalence have been on a steady rise. This is partly due to the increase in new dietary habits and routines and a more sedentary lifestyle incorporated by the modern man. The prevalence of metabolic diseases has risen to almost a third of the population in the United States. At the same time, this number remained roughly the same until the year 2016; a concerning increase in the number of young adults with MetS has been observed, which will have rippling effects in the future of the MetS epidemic.24,25 This increase is not limited to the United States or the West but is seen throughout the globe, such as in China and the Asian Pacific regions.26,27 Given the rise in prevalence, it is not surprising that numerous patients with MetS are undergoing spine surgery.15 Amplifying this, patients with MetS experience spinal osteoarthritis and disc degeneration (DD) at a higher rate compared with the rest of the population. Furthermore, while each component of MetS can increase spinal osteoarthritis individually, their combined effect is also significant.8,9 This, in turn, will increase the number of spinal surgeries done on MetS patients 3-fold.21 MetS patients also have an extra financial burden when undergoing spinal surgeries, with an increase of 16.4% in costs related to the surgery.22
To the extent of the search, this is the first meta-analysis conducted on this topic, making it distinctive. However, meta-analyses have been conducted on how MetS can affect postoperative outcomes. In a 2016 meta-analysis, it was concluded that MetS can increase graft rejection and cardiovascular events in renal transplantation.28 In another meta-analysis, it was found that MetS can increase adverse events after colorectal surgeries.29 Meta-analyses on orthopedic surgeries show MetS worsens postoperative outcomes, especially in knee arthroplasties. Patients with MetS have longer hospital stays, higher all-cause complications, and increased risk of deep vein thrombosis.30,31 Although no literature shares the exact goal of this study, 2 studies examined how diabetes and obesity influence postoperative outcomes in spinal surgeries. Both findings indicate that these aspects of MetS impair postoperative recovery.32,33
HTN, diabetes, obesity, and DL, being the components of MetS, have been independently investigated for adverse surgical outcomes in spine procedures in 2 studies.1,17 Naessig et al assessed the individual and synergistic roles of these components, stating HTN as the most effective predictor of complications. Patients with uncontrolled HTN had elevated odds of perioperative adverse events, with risk reduction observed when managed. Diabetes was also another influential factor, amplifying infection and impaired wound healing risks. Obesity exhibited a more pronounced impact when coexisting with HTN or diabetes. DL contributed to thrombotic complications when combined with other MetS components.17
Similarly, Lovecchio et al stated that HTN and diabetes were independently associated with increased rates of surgical site infections and systemic complications, even after adjusting for obesity. Their findings suggest that the proinflammatory effects of these conditions, rather than obesity on its own, underlie their adverse surgical impact. For instance, diabetic patients exhibited higher incidences of urinary tract infections and sepsis, likely reflecting the role of glycemic dysregulation in immune dysfunction. HTN, related to endothelial dysfunction and impaired tissue perfusion, correlated with delayed wound healing and cardiovascular events.1
This study found that MetS has negative consequences on postoperative outcomes, including increased length of stay, increased need for repeat surgery, surgical site infections, urinary tract infections, and 30-day readmission. This study also demonstrates how pulmonary complications increase in MetS patients; however, due to the comorbidity of chronic obstructive pulmonary disease and MetS, these complications can be attributed to chronic obstructive pulmonary disease.34 Further studies are needed to contrast the effects of chronic obstructive pulmonary disease and MetS on surgical outcomes.
The findings of this study were consistent with previous studies showing that MetS can increase postsurgical infections.30,35 The pathology of how MetS can increase infections is related to increased adiposity in these patients, as the endocrine imbalance causes constant inflammation. This study showed that higher rates of surgical site and urinary tract infections were associated with MetS. Analyzing each component separately, being overweight was linked to DD across the entire spine. HTN and impaired glucose tolerance were associated with DD only in the thoracic spine. DL had a negative association with thoracic DD, which was controversial. The risk of thoracic DD increased with more MetS components, with individuals having more components showing higher odds of degeneration.
Also, the meta-analysis showed that length of stay, readmissions, and reoperations increase in patients with MetS. While the cost of these complications was not assessed in the included studies, it is reasonable to hypothesize that expenses were higher for these patients. Since spine surgery is already costly, this could raise economic concerns for health officials worldwide. The incidence of MetS is increasing in all countries, regardless of their financial status.36 Postoperative complications might pose a greater financial burden on low-income countries. The studies included in this meta-analysis involved patients in academic centers within countries that have adequate financial resources; additional research should be conducted to assess the impact of MetS on surgeries worldwide.
This study is limited by biases in the selected studies, such as selection bias in the NSQIP and a lack of individual patient data. NSQIP’s 30-day follow-up scope is limited. Although MetS is well studied, its definition is not universal. Most studies used the NSQIP definition, but other definitions, like those of the International Diabetes Federation and World Health Organization, exist. Comparing these could reveal differences in postoperative complications.37 It is also worth mentioning that most of the studies conducted were done in academic centers, and it would be essential to expand the horizons with studies in more rural areas to conclude how MetS can affect spine surgeries. The heterogeneity in our analyses highlights the need for careful interpretation. This variability mainly arises from differences within the included studies, such as the broad category of “spine surgery” covering procedures from minimally invasive decompressions to extensive fusions, each with distinct risks. Variations in defining MetS, patient demographics, and follow-up durations also contribute to statistical inconsistencies. Therefore, our meta-analysis offers a general overview, and results should be seen as indicative of trends rather than exact risk estimates for specific procedures or groups.
Another limitation in our study is the aggregation of outcomes across diverse spine procedures without distinguishing between surgical approaches (anterior, posterior, or combined) or surgery types (fusion and decompression) or isolating the effects of MetS components. Most studies combine results from decompressions, single-level fusions, and multilevel instrumentations while treating MetS as a single entity rather than analyzing the distinct impacts of HTN, diabetes, DL, and obesity. These discrepancies among the studies caused high heterogeneity that should be considered when interpreting the results. It would be beneficial for future studies to report the complication rates separately for various approaches and types of spine procedures and components of MetS.
Conclusion
MetS could be considered a significant risk factor for postoperative medical and surgical complications in patients undergoing spine surgery. MetS significantly increased 30-day readmission and reoperation, as well as VTE, cardiac, respiratory, cerebrovascular, renal, urinary, and wound complications. However, mortality, nonhome discharge, pneumonia, sepsis, and transfusion needs were comparable between the 2 groups of patients. Future studies with more extended follow-up periods and a more diverse population are warranted to further instigate the impact of MetS on long-term outcomes following spine surgery. Furthermore, the optimized management of MetS spine surgery candidates and their role in enhancing postoperative outcomes should be investigated in future studies.
Supplementary material
online supplementary file 1.
Footnotes
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The authors report no conflicts of interest in this work.
Study Protocol The protocol of this study was registered in PROSPERO (CRD42024606549).
- This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2025 ISASS. To see more or order reprints or permissions, see http://ijssurgery.com.
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