Introduction

Cigarette smoking is a significant public health concern worldwide. Approximately 20% of adults in the US currently smoke cigarettes, which are responsible for up to 20% of all deaths each year1. In some cervical surgeries, more than half of the patients are smokers2,3,4. Smoking is highly detrimental to health and is associated with cancer, respiratory disease, and cardiovascular disease5. A growing body of evidence shows that smoking is a significant risk factor for adverse surgical outcomes after spine surgery5,6,7,8.

The relationship between smoking and outcomes of cervical surgery has not been well evaluated. Some studies suggest that smoking may be associated with poorer outcomes after cervical surgery, including lower fusion rates9,10. Smoking has been independently linked to higher volumes of blood loss11, longer lengths of stay2,11, and higher reoperation rates12,13. There is also an increased risk of perioperative complications, including dysphagia, airway obstruction, nerve palsy, reintubation, axial neck pain, wound infection, deep venous thrombosis, pneumonia, and pseudarthrosis7,11,12,14,15,16,17. Pain control and functional outcomes have also been shown to be less favorable in smoking patients18,19.

Nevertheless, some studies disputed these findings and suggested no relationship between smoking and adverse surgical outcomes after cervical surgery18,20,21. Some researchers even found that the incidence of complications in smokers was lower than that in nonsmokers after posterior cervical fusion22. We performed the present study to resolve these discrepancies. To the best of our knowledge, there have been no previous systematic reviews and meta-analyses that assess the association between smoking and outcomes of cervical spine surgery.

Materials and methods

Literature search strategy

This meta-analysis was performed in accordance with the Meta-analysis of Observational Studies in Epidemiology (MOOSE) statement23. The PubMed, Embase, Cochrane Library, and Web of Science electronic databases were searched from inception to 13 July 2021 using the MeSH terms “smoking,” “cervical vertebrae,” “surgical procedures, operative,” and their corresponding free terms. The search was restricted to human subjects. In addition, we also reviewed the list of references for retrieved papers and recent reviews.

Inclusion and exclusion criteria

The inclusion criteria were as follows: (1) The study design was cohort studies, case–control studies, or controlled or comparative studies; (2) the study population consisted of smokers and nonsmokers who underwent cervical spine surgery; and (3) the study compared outcomes, including operating time, pain score, functional score, reoperation, length of hospital stay, estimated blood loss, fusion, and postoperative complications. The exclusion criteria were as follows: (1) reviews, letters, case reports, systematic reviews, animal studies, noncomparative studies, and studies that were unrelated to our topics; (2) the study did not involve any of the outcomes listed in the inclusion criteria; and (3) duplicated publications from the same hospital or research center. For accepted articles that covered the same population or subpopulation, the most informative articles or complete studies were used to prevent duplication of information.

Data extraction

Data extraction was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, and the selection of articles and the extraction of data were carried out independently by two reviewers and examined by other authors. Any disagreements were resolved by consensus or discussion with a third reviewer. The following information was extracted from the studies: (1) the general study information (name of the first author, publishing date, country, study design, sample size, age, sex, surgical procedure, follow-up time, and definition of smoking); (2) perioperative parameters, including operative time, estimated blood loss, and length of hospital stay; (3) clinical outcomes, including visual analog scale (VAS) scores of neck pain and arm pain, Neck Disability Index (NDI) score, and Japanese Orthopedic Association Scores (JOA); (4) complications, fusion and reoperation; the complications were defined as primary outcomes in this study, including dysphagia, airway obstruction, nerve palsy, reintubation, axial neck pain, wound infection, deep venous thrombosis, pneumonia, and pseudarthrosis. For continuous outcomes, we extracted the mean and standard deviation, and participant numbers were also extracted. For dichotomous outcomes, we extracted the total numbers and the numbers of events of both groups. The data in other forms was recalculated when possible to enable pooled analysis.

Methodological quality

Reviewers applied the Newcastle–Ottawa Scale (NOS) to evaluate the methodological quality of the included studies24. The NOS is a scoring checklist for solving design and implementation issues of a cohort or case–control study, which consisted of participant selection, comparability of cases and controls, exposure, and outcomes. If the study was awarded six or more stars, it was considered a high-quality study and was analyzed.

Statistical analysis

We used STATA version 12.0 (StataCorp, College Station, TX) to generate forest plots to determine whether there was a statistical association between the case and control groups and to assess heterogeneity of the included studies. Dichotomous outcomes were expressed as effect estimates (ESs) with 95% confidence intervals (CIs); among them, the results of case–control studies are expressed as odds ratios (ORs), and the results of cohort studies are expressed as relative risks (RRs); continuous outcomes are expressed as the weighted mean differences (WMDs). Heterogeneity was quantified using the chi-square based Cochran’s Q statistic25 and the I2 statistic, which yields results ranged from 0 to 100% (I2 = 0–25%, no heterogeneity; I2 = 25–50%, moderate heterogeneity; I2 = 50–75%, large heterogeneity; and I2 = 75–100%, extreme heterogeneity)26. In cases of substantial heterogeneity, the random-effects model was applied. Otherwise, the fixed-effects model was used. When heterogeneity was present, a ‘leave-one-out sensitivity analysis was performed by iteratively removing one study at a time to confirm the source of the heterogeneity. Analysis was then performed without the study to determine if heterogeneity was still present and if so, random-effects modeling was used. Publication bias was assessed using visual inspection of the funnel plot with the Begg27 and Egger tests28. All statistical tests were two-sided, and p-values of < 0.05 were considered statistically significant.

Results

Identification of eligible studies

A flowchart of the search and study selection process is shown in Fig. 1. The electronic search identified a total of 352 citations (69 from PubMed, 212 from EMBASE, 20 from the Cochrane Library, and 51 from the Web of Science). After screening titles and abstracts and removal of duplicates, 122 were considered of interest; the full text of these 122 studies was retrieved for detailed evaluation; 79 studies were excluded, and 43 studies were ultimately included in the meta-analysis2,3,4,7,9,10,11,12,13,14,15,16,18,19,20,21,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55.

Figure 1
figure 1

Flow diagram of study selection.

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Characteristics of included studies

The characteristics of the studies are summarized in Table 1. The 43 independent observational studies included in this meta-analysis were published from 1995 to 2021. These forty-three studies included 10,020 patients, including 3,107 smokers and 6,913 nonsmokers. Twenty-seven studies were conducted in the United States and seven were conducted in China. The other nine were conducted in India, Japan, the Czech Republic, Italy, Korea, Singapore, and Taiwan. Of these, 16 were cohort studies, and 27 were case–controls. All raw data are available in the Supplementary Tables S1 and S2.

Table 1 Baseline characteristics of included studies.
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Quality of included studies

Because all the included studies were cohort studies or case–control studies, the quality of each study was evaluated using the NOS (maximum of nine stars). Case–control studies were divided into three categories: selection, comparability, and exposure, and cohort studies were divided into three categories: selection, comparability, and outcomes. According to the NOS scale, all included studies were considered to be of high-quality: 12 were awarded eight stars, 10 were awarded seven stars, and 5 were awarded six stars in case–control studies (Table 2). Nine were awarded eight stars, 3 were awarded seven stars, and 4 were awarded six stars in cohort studies (Table 3).

Table 2 Quality assessment of case–control studies according to Newcastle–Ottawa scale.
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Table 3 Quality Assessment of Cohort Studies According to Newcastle–Ottawa Scale.
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Meta-analysis

Overall complications

The primary outcomes in our meta-analysis were complications, including dysphagia, airway obstruction, nerve palsy, reintubation, axial neck pain, wound infection, deep venous thrombosis, pneumonia, deltoid weakness, tracheobronchitis, and pseudarthrosis. At least one postoperative complication was reported in 20 studies2,3,11,12,14,16,18,20,21,29,33,34,35,38,40,42,43,47,51,52. Significant heterogeneity was observed, and the random-effects model was used (I2 = 50.8%, p = 0.005). The meta-analysis revealed that smokers were significantly associated with postoperative complications compared with nonsmokers (ES = 1.96, 95% CI: 1.45–2.66, p < 0.001). Because of the heterogeneity (I2 = 50.8%), a sensitivity analysis was performed. The study of Reinard et al.2 excluded patients with a recombinant human bone morphogenetic protein associated with dysphagia after cervical surgery56. It may affect the incidence of postoperative dysphagia. Excluding this paper reduced I2 to 45.3% (Fig. 2). Reanalysis using a fixed-effects model revealed that, compared with nonsmokers, smokers were significantly associated with postoperative complications (ES = 1.99, 95% CI: 1.62–2.44, p < 0.0001).

Figure 2
figure 2

Forest plot showing the effect of smoking on overall complications. OR, odd rate; RR, risk rate; CI, confidence interval.

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Respiratory complications

Six studies reported postoperative respiratory complications, including dyspnea, reintubation, airway obstruction, pneumonia, and tracheotomy7,11,20,34,47,52. There was significant heterogeneity (I2 = 51.4%, p = 0.068); therefore, the random-effects model was used. Pooling of the results demonstrated that smokers were more associated with respiratory complications than nonsmokers (ES = 2.30, 95% CI: 1.05–5.05, p = 0.038). After performing sensitivity analysis and removing the study by Sagi et al.52 a higher proportion of patients who had exposure of C4 or above compared with other studies, the heterogeneity was reduced to 31.2% (Fig. 3). Fixed-effects modeling showed that smokers were significantly more associated with respiratory complications than nonsmokers (ES = 2.70, 95% CI: 1.62–4.49, p < 0.0001).

Figure 3
figure 3

Forest plot showing the effect of smoking on respiratory complications. OR, odd rate; RR, risk rate; CI, confidence interval.

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Reoperation

The number of patients who underwent reoperation was provided in eight studies4,11,12,13,20,41,46,49. Significant heterogeneity was observed, and a random-effects model was used (I2 = 57.7%, p = 0.020). Pooling of the results demonstrated that smokers were more associated with reoperation than nonsmokers (ES = 1.80, 95% CI: 1.06–3.06, p = 0.0029). When performing statistical analysis of Mangan et al.46, we defined the sum of current and former smokers as the total number of smokers. We then removed Mangan et al., performed a sensitivity analysis, and found that heterogeneity was reduced to 41.4% (Fig. 4). Reanalysis using a fixed-effects model revealed that smokers were significantly more associated with reoperation after cervical spine surgery than nonsmokers (ES = 2.06, 95% CI: 1.50–2.81, p < 0.001).

Figure 4
figure 4

Forest plot showing the effect of smoking on reoperation. OR, odd rate; RR, risk rate; CI, confidence interval.

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Fusion

Sixteen studies performed cervical fusion surgery and reported fusion9,10,11,19,20,30,31,32,36,37,45,46,50,53,54,55. No significant heterogeneity was observed, and a fixed-effects model was used (I2 = 38.2%, p = 0.061). Pooling of the results demonstrated that after cervical fusion surgery, there was no significant difference in fusion between the smoking group and the nonsmoking group (ES = 0.97, 95% CI: 0.94–1.00, p = 0.097; Fig. 5).

Figure 5
figure 5

Forest plot showing the effect of smoking on fusion. OR, odd rate; RR, risk rate; CI, confidence interval.

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Dysphagia

Eight studies reported dysphagia after cervical spine surgery2,3,16,18,20,33,51. No significant heterogeneity was observed, and a fixed-effects model was used (I2 = 46.9%, p = 0.0068). Pooling of the results demonstrated that smokers were more associated with postoperative dysphagia than nonsmokers (ES = 1.49, 95% CI: 1.06–2.10, p = 0.022; Fig. 6).

Figure 6
figure 6

Forest plot showing the effect of smoking on dysphagia. OR, odd rate; RR, risk rate; CI, confidence interval.

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Wound infection

Seven studies reported postoperative wound infection7,11,12,14,18,29,35. No significant heterogeneity was observed, and a fixed-effects model was used (I2 = 17.0%, p = 0.300). Pooling of the results demonstrated that smokers were significantly more associated with postoperative wound infection than nonsmokers (ES = 3.21, 95% CI: 1.62–6.36, p = 0.001; Fig. 7).

Figure 7
figure 7

Forest plot showing the effect of smoking on wound infection. OR, odd rate; RR, risk rate; CI, confidence interval.

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Axial neck pain

Three studies reported postoperative axial neck pain15,39,44. Significant heterogeneity was observed, and a random-effects model was used (I2 = 63.7%, p = 0.064). Pooling of the results shows that compared with nonsmokers, smokers had no significant correlation with axial neck pain after cervical spine surgery. (ES = 1.54, 95% CI: 0.75–3.16, p = 0.236). After performing sensitivity analysis and removing the study by Liu et al.44 the only article on anterior cervical surgery, the heterogeneity was reduced to 38.9% (Fig. 8). Fixed-effects modeling revealed that the smoking group was significantly more associated with axial neck pain than the nonsmoking group (ES = 1.98, 95% CI: 1.25–3.12, p = 0.003).

Figure 8
figure 8

Forest plot showing the effect of smoking on axial neck pain. OR, odd rate; RR, risk rate; CI, confidence interval.

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Operation time

The operation time was provided in two studies21,48. No significant heterogeneity was observed, and a fixed-effects model was used (I2 = 0.0%, p = 0.955). Pooling of the results revealed no significant difference in operation time after cervical spine surgery between smokers and nonsmokers (WMD = 0.08, 95% CI: −5.54 to 5.71, p = 0.955; Supplementary Fig. S1a).

Estimated blood loss

The estimated blood loss was provided in three studies2,11,48. Significant heterogeneity was observed, and a random-effects model was used (I2 = 66.1%, p = 0.053). Pooling of the results revealed no significant difference in estimated blood loss after cervical spine surgery between smokers and nonsmokers (WMD = −5.31, 95% CI: −148.83 to 139.22, p = 0.943; Supplementary Fig. S1b). After performing leave-one-out sensitivity analysis, the heterogeneity did not change substantially and remained significant.

Length of hospital stay

The length of hospital stay was provided in four studies2,11,21,48. Significant heterogeneity was observed, and a random-effects model was used (I2 = 88.3%, p < 0.0001). Pooling of the results revealed no significant difference in the length of hospital stay after cervical spine surgery between smokers and nonsmokers (WMD = 1.01, 95% CI: −2.17 to 4.20, p = 0.534; Supplementary Fig. S1c) . After performing leave-one-out sensitivity analysis, the heterogeneity did not change substantially and remained significant.

VAS: neck pain

VAS-neck pain was reported in two studies18,48. No significant heterogeneity was observed, and a fixed-effects model was used (I2 = 0.0%, p = 0.530). Pooling of the results revealed no significant difference in VAS-neck pain after cervical spine surgery between smokers and non-smokers (WMD = −0.19, 95% CI: −1.19 to 0.81, p = 0.707; Supplementary Fig. S1d) .

VAS: arm pain

VAS-arm pain was reported in two studies18,48. No significant heterogeneity was observed, and a fixed-effects model was used (I2 = 0.0%, p = 1.000). Pooling of the results revealed no significant difference in VAS-arm pain after cervical spine surgery between smokers and nonsmokers (WMD = −0.50, 95% CI: −1.53 to 0.53, p = 0.343; Supplementary Fig. S1e).

NDI

NDI was reported in four studies18,19,21,48. Significant heterogeneity was observed, and a random-effects model was used (I2 = 96.4%, p < 0.0001). Pooling of the results revealed no significant difference in NDI after cervical spine surgery between smokers and nonsmokers (WMD = 11.46, 95% CI: −3.83 to 26.76, p = 0.142; Supplementary Fig. S1f.). After performing leave-one-out sensitivity analysis, the heterogeneity did not change substantially and remained significant.

JOA

JOA was reported in two studies18,21. Significant heterogeneity was observed, and a random-effects model was used (I2 = 89.4%, p = 0.002). Pooling of the results revealed no significant difference in JOA after cervical spine surgery between smokers and nonsmokers (WMD = −1.75, 95% CI: −5.27 to 1.78, p = 0.332; Supplementary Fig. S1g). Each specific result can be found in Table 4.

Table 4 Results of the meta-analysis.
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Subgroup analysis

For primary outcomes, we conducted subgroup analysis based on the type of study. The results of four cohort studies were expressed as RR, and smoking had adverse effects on overall complications (RR = 2.55, 95% CI: 1.52–4.27, p < 0.0001). After removing one article, a total of 15 case–control studies were included. The results were expressed as ORs. Compared with nonsmokers, smokers were significantly more correlated with the overall complications after cervical spine surgery (OR = 1.90, 95% CI: 1.52–2.38, p < 0.0001).

Publication bias

The Begg rank correlation test and Egger linear regression test indicated no evidence of significant publication bias among the included studies (Egger p = 0.266; Begg p = 0.266; Supplementary Fig. S2A, S2B).

Discussion

The major purpose of the present meta-analysis was to determine whether smoking has adverse effects on surgical outcomes after cervical spine surgery. Our results suggest that smoking is associated with reoperation and postoperative complications, including dysphagia, axial neck pain, and wound infection. Compared with nonsmokers, smokers were more associated with overall postoperative complications and respiratory complications. There were no significant differences between smokers and nonsmokers concerning outcomes, including fusion, operation time, estimated blood loss, length of hospital stay, VAS-neck pain score, VAS-arm pain score, NDI score, or JOA score. Our results suggest that smoking might have adverse effects on surgical outcomes in patients who undergo cervical spine surgery.

Complications were the primary outcomes used to evaluate the safety of cervical spine surgery among smoking patients. Siemionow et al. conducted a study of 35 patients undergoing anterior and posterior cervical decompression and fusion and reported that smoking appeared to be the most critical factor related to perioperative complications; the risks for at least one perioperative complication were 50% and 31.6% for smokers and nonsmokers, respectively7. Lau et al. studied 160 patients undergoing anterior cervical corpectomy and found that smoking patients had longer hospital stays, more bleeding, a higher rate of pseudarthrosis, and more complications at 30 days than nonsmoking patients11. In contrast, Fehlings et al. analyzed data from the AOSpine North America Cervical Spondylotic Myelopathy Study and concluded that perioperative complications were not associated with smoking status57. Medvedev et al. reported the complication rates in smoking and nonsmoking patients of 23.5% and 39.8% (p < 0.0001), respectively22. Our pooled data showed that smoking was associated with increased postoperative complications, including dysphagia, airway obstruction, nerve palsy, reintubation, axial neck pain, wound infection, deep venous thrombosis and pneumonia.

We assessed perioperative outcomes, including fusion, operation time, estimated blood loss, and length of hospital stay in our meta-analysis and failed to find any significant difference between the smoking and nonsmoking groups. As measured by NDI, JOA, and VAS scores, functional recovery was similar between the two groups. This finding indicates that cervical spine surgery might offer similar functional outcomes in smoking patients. However, only two articles reported VAS-neck pain and JOA scores, one study found that smoking improved both VAS-neck pain and JOA scores, while the other found the opposite. Therefore, more articles can improve the accuracy of the conclusion, and the relatively small sample size limited the generalizability of this conclusion.

After cervical spine surgery, smokers were closely associated with reoperation. In this meta-analysis, given that functional improvement between the groups was similar, it is possible that reoperation was directly related to complications in smoking patients, including wound infection, respiratory complications, and pseudarthrosis. However, due to limited data, we did not perform a subgroup analysis based on the type of surgical procedure.

There are several potential explanations for the observed association between smoking and adverse effects on the surgical outcomes for patients after cervical spine surgery. First, cigarette smoke products have been shown to inhibit prostacyclin production, a potent vasodilator, and an inhibitor of platelet aggregation. This effect can lead to impaired blood flow and increased blood viscosity, which result in impaired blood supply58,59,60,61,62, and leads to decreased angiogenesis and epithelialization63. Moreover, inhibition of revascularization by nicotine was observed in a rabbit study, and this mechanism may retard cellular metabolism and promote tissue degeneration64.

Second, at the cellular level, nicotine has been shown to inhibit proliferation, differentiation, and collagen synthesis in osteoblasts65, which is the primary determinant of the tensile strength of a surgical wound66. Free radicals produced by burning cigarettes have been associated with cell membrane destabilization, impaired osteoblast mitochondrial oxidative function and local tissue hypoxia58,67,68,69,70,71.

Third, it is well-documented that smoking harms bone physiology, which result in decreased bone mineral density, impaired bone metabolism, and accelerated osteoporosis, with produces lower fusion rates72. Animal and in vitro studies found that nicotine impaired bone healing, retarded bone formation and growth, and decreased graft biomechanical properties73,74.

Finally, cigarette smoke contains many toxic ingredients. Nicotine, tar, and other components irritate mucous membranes of the respiratory tract and cause cilia of bronchial epithelial cells to become shorter and irregular, which can hinder the movement of ciliary bodies, reduce local resistance, and weaken phagocytosis and sterilization functions of alveolar phagocytes, which leads to bronchospasm and increased airway resistance75. For these reasons, smokers are susceptible to respiratory complications after cervical spine surgery. In addition, carbon monoxide combines with hemoglobin, which reduces the oxygen-carrying capacity of the blood, and hydrogen cyanide inhibits cytochrome c, and leads to inhibition of aerobic metabolism76.

To the best of our knowledge, our meta-analysis, on the basis of 16 cohort studies and 27 case–control studies, is the first, also the largest and most comprehensive assessment to investigate the association between smoking and outcomes of cervical spine surgery. The main strength of this systematic review and meta-analysis is the thorough literature search, careful study selection with strict inclusion criteria, and comprehensive assessment of methodological quality of included studies using the NOS, which is, currently, the accepted standard. In addition, we performed subgroup analysis according to the type of study for the primary outcomes. Although we found significant heterogeneity in several outcomes among the included studies, the sensitivity analysis showed no significant change, which suggested that the pooled estimate in our study was stable. Finally, publication bias was quantitatively evaluated using Begg’s and Egger’s linear regression tests.

This systematic review and meta-analysis have several limitations that are worthy of comment. First, studies included in our review spanned over two decades (1995 to 2021), during which advancements in cervical surgery techniques might have improved outcomes. Despite this, point estimates for earlier and more recent studies were similar. Second, all of the included studies were retrospective observational trials rather than randomized controlled trials. The inherent nature of observational trials may be associated with selective bias, which might have influenced our results. Third, in most studies, the definition of smoking was not standardized, and self-reporting introduces recall bias or response bias because nonsmokers may be current or former smokers. Therefore, the true impact of smoking may be larger than we have reported here. Moreover, the definition of complications was not uniform and might introduce an additional source of bias. Fourth, since most of the information collected was not used to answer specific questions, all characteristics of smoker and nonsmoker cohorts such as age, sex, BMI, ethnic group, indications for surgery, and comorbidities, were not necessarily consistently matched, leaving some possible residual confusion, resulting in high heterogeneity. Moreover, due to the limited number of articles, we did not compare the various types of cervical spine surgeries in detail. In addition, only two studies reported operation time, VAS-neck pain, VAS-arm pain and JOA, and only three studies reported estimated blood loss and axial neck pain. Their results were based on a very small number of studies, which may lack reference value. Finally, we do not know how investigators confirmed that their patients did not smoke before or after surgery or even if they quit smoking before surgery, which may have impacted the evaluated results.

One study analyzed the pack-year history and found that, after lumbar surgery, nicotine exposure was associated with an increased risk of disease, and there was a dose–response trend; however, this trend was not significant77. In contrary, another study did not support this view and found that after anterior cervical discectomy and fusion, pack-years were not significantly associated with greater odds of developing any one complication or any major complication78. This may be related to differences in the number, characteristics, surgical sites, and follow-up time of the population included in the study. Therefore, there is an urgent need for further high-quality studies that are sufficiently prepared and designed with sufficient detail to adjust for multiple confounders and allow exploration of dose–response relationships.

Some researchers reported that preoperative smoking cessation might improve surgery outcomes and could lower medical costs by decreasing postoperative complications and length of post surgical hospital stay among smokers11,79. Sørensen et al. performed a meta-analysis and found that smoking cessation reduced the risk of surgical site infection in plastic and general surgery patients by more than half80. Andersen et al. found that quitting smoking significantly increased the rate of fusion after spinal surgery compared to those who continued to smoke, bringing it close to the level of nonsmokers81. This may be related to the rapid recovery of local tissue oxygenation and metabolism after smoking cessation82. Therefore, it is theoretically necessary to quit smoking before elective surgery.

Nevertheless, the optimal timing to quit smoking remains a matter of considerable debate. A study showed that quitting smoking 1 to 2 months before surgery can significantly reduce the perioperative risk77. Some studies indicated that smoking cessation must be at least 4 weeks before surgery to be effective83,84. Another study said that smoking cessation should be carried out at least 2 months before coronary artery bypass to maximize the reduction of postoperative respiratory complications85. Jung et al. found that preoperative smoking cessation for at least 2 weeks will help to reduce the incidence of postoperative complications in gastric cancer surgery86. Thus, exploring the optimal timing to quit smoking before the operation should determine future efforts.

Conclusions

Compared with nonsmokers, smokers seem to be more significantly associated with overall complications, respiratory complications, reoperation, longer hospital stay, dysphagia, wound infection and axial neck pain after cervical spine surgery. Our results suggest that smoking is closely related to adverse consequences after cervical spine surgeries. It is crucial to provide timely smoking cessation advice and explanation to patients before elective cervical surgery.