Orthopedics

Feature Article 

Effect of Nicotine Dependence and Smoking on Revision Diskectomy After Single-Level Lumbar Diskectomy

Eric J. Smith, MD; Bradley P. Inkrott, MD; Jerry Y. Du, MD; Uri M. Ahn, MD; Nicholas U. Ahn, MD

Abstract

Removal of a herniated disk that is causing neural compression is among the most common indications for spinal surgery. Previous population database studies of risk factors for reoperation after this procedure analyzed small to medium numbers of patients. To date, no study has concurrently assessed the effect of modifiable risk factors, such as smoking and nicotine dependence, with a large number of patients. Data were obtained with commercially available software that houses de-identified data for several major US health care systems. A database search was conducted to find all patients who had undergone lumbar diskectomy. Obesity, scoliosis, spondylolisthesis, and depression were excluded as possible confounding variables. The remaining patients were divided into smoking and nonsmoking groups. Those who had undergone revision lumbar diskectomy within 2 years were counted. Pearson's chi-square statistical test was used to determine significance at P<.05. Of the 50 million patient records in the software platform, 53,360 patients were identified who had undergone single-level lumbar diskectomy. Of these, 26,980 fulfilled the inclusion criteria. A total of 890 of those patients had undergone revision lumbar diskectomy within 2 years of their original procedure. Those who smoked were found to have a relative risk of 2.47 compared with nonsmokers (95% confidence interval, 2.17–2.82; P<.0001). Nicotine dependence and smoking had a significant effect on the rate of reoperation. These findings support the importance of preoperative assessment of modifiable risk factors and their effects on surgical complications. [Orthopedics. 2020;43(5):e438–e441.]

Abstract

Removal of a herniated disk that is causing neural compression is among the most common indications for spinal surgery. Previous population database studies of risk factors for reoperation after this procedure analyzed small to medium numbers of patients. To date, no study has concurrently assessed the effect of modifiable risk factors, such as smoking and nicotine dependence, with a large number of patients. Data were obtained with commercially available software that houses de-identified data for several major US health care systems. A database search was conducted to find all patients who had undergone lumbar diskectomy. Obesity, scoliosis, spondylolisthesis, and depression were excluded as possible confounding variables. The remaining patients were divided into smoking and nonsmoking groups. Those who had undergone revision lumbar diskectomy within 2 years were counted. Pearson's chi-square statistical test was used to determine significance at P<.05. Of the 50 million patient records in the software platform, 53,360 patients were identified who had undergone single-level lumbar diskectomy. Of these, 26,980 fulfilled the inclusion criteria. A total of 890 of those patients had undergone revision lumbar diskectomy within 2 years of their original procedure. Those who smoked were found to have a relative risk of 2.47 compared with nonsmokers (95% confidence interval, 2.17–2.82; P<.0001). Nicotine dependence and smoking had a significant effect on the rate of reoperation. These findings support the importance of preoperative assessment of modifiable risk factors and their effects on surgical complications. [Orthopedics. 2020;43(5):e438–e441.]

Surgical removal of a herniated disk that is causing neural compression is one of the most common indications for spinal surgery. Previous studies looked at the rate of reoperation for lumbar diskectomy and reported a range of 5% to 15%.1–10 Nicotine dependence and smoking are known risk factors for complications of spinal surgery, but although their effects on spinal fusion and fracture healing are well studied, the data are mixed on decompressive procedures.11

Many large population database studies have quantified the risk of reoperation after single-level lumbar diskectomy. The largest population study identified 35,309 patients who had undergone single-level lumbar diskectomy.3 Kim et al2 studied 18,590 patients and Heindel et al1 identified 13,654 patients who had been treated with lumbar diskectomy. Of all of these studies examining revision diskectomy, few have considered the effects of modifiable risk factors, including nicotine dependence and smoking. Both Leven et al6 and Abdu et al7 analyzed the data for 810 patients from the Spine Patient Outcomes Research Trial (SPORT) to identify risk factors affecting the rates of reoperation and revision surgery. These studies found no increased risk of reoperation with smoking.

The goal of the current study was to examine the effect of smoking on the reoperation rate after single-level lumbar diskectomy with data collected from Explorys (IBM, Armonk, New York). Unlike most other large population databases, such as the Medicare 5% National Sample Administrative Database or the Humana Inc (HORTHO) database, which are derived from a single center or a single insurance provider, Explorys is a multi-institutional database that contains data from multiple insurance providers. It is expected that, with Explorys, data on a much larger set of patients can be collected compared with any previous study that examined smoking as a risk factor for revision lumbar diskectomy. This larger set of data should better identify factors that may affect outcomes.

Materials and Methods

The commercially available software platform Explorys was used to obtain the study data. Explorys supports every major electronic health record platform and contains data from multiple major US health systems. The information is housed in an aggregated and de-identified format. To comply with the Health Insurance Portability and Accountability Act, patient numbers for all groups are rounded to the nearest 10. To date, the database contains information from more than 50 million patients.

The Explorys database was queried on May 20, 2018, for all patients who had undergone single-level lumbar diskectomy. Explorys allows users to search the database in a variety of ways, including the use of Current Procedural Terminology codes, diagnosis names, and procedure names. The input “Procedure: Primary Lumbar Discectomy” was used to search for the desired group of patients. Four cohorts were then created to assess the effects of smoking on the reoperation rate.

Multiple exclusion criteria were used to help to eliminate confounding factors. Each cohort excluded patients with obesity, scoliosis, spondylolisthesis, and depressive disorder. Of the cohorts, 2 included only those with “Finding: Smoker,” whereas the other 2 excluded anyone with this finding. The smoking and non-smoking groups each contained 1 cohort that included those who underwent “Procedure: Revision Lumbar Discectomy” within 2 years of the original lumbar diskectomy. The other 2 cohorts excluded patients who had undergone any revision lumbar diskectomy within 2 years.

The entire smoking group was compared with the nonsmoking group based on mean age, age distribution, sex, and race to ensure similarity between the groups. Rates of reoperation were calculated for both the smoking and nonsmoking groups as well as for the entire group of smokers and nonsmokers combined. Pearson's chi-square statistical test was used to determine significance at P<.05, and relative risk and confidence interval were determined for smokers vs nonsmokers. All statistical calculations were performed with R, version 3.5.0 (R Foundation, Vienna, Austria).

Results

Of the total of 53,360 patients who underwent primary lumbar diskectomy, 26,980 met the inclusion criteria. These patients were divided into smokers and nonsmokers and were compared by age distribution, race, and sex. The groups had similar mean age and sex and racial distributions. Mean age of the nonsmoking group was 56.2 years, whereas mean age of the smoking group was 55.2 years. Likewise, of the smoking group, 69.6% were men, whereas of the nonsmoking group, 63.1% were men. The racial breakdown also was similar between the two groups (Table 1). Given this uniformity between the cohorts, the authors were confident that any differences between groups would be related to smoking, the independent variable in question.

Demographic Features of the Patient Groups

Table 1:

Demographic Features of the Patient Groups

Reoperation rates were calculated for various groups from the entire Explorys database as well as for smokers and non-smokers with the applied exclusions. The overall reoperation rate for all 53,360 patients who had undergone single-level lumbar diskectomy in the Explorys database was 8.8%. Of those patients, 2380 had a revision within 2 years, making the 2-year revision rate in the Explorys database 4.5%. When exclusions were applied, 26,980 patients were found to have undergone a single-level lumbar diskectomy that also fit the inclusion criteria. Of this group, 890 patients, or 3.3%, underwent a revision within 2 years. A total of 5600 smokers and 21,380 nonsmokers fit the inclusion criteria, with 350 and 540, respectively, undergoing revision diskectomy within 2 years. Those who smoked had a higher 2-year revision rate of 6.3%, whereas nonsmokers had a 2-year revision rate of 2.5%. The smoking group had a higher incidence of reoperation, with relative risk of 2.47 (95% confidence interval, 2.17–2.82; P<.0001), compared with nonsmokers.

Discussion

This study is the first and largest to date to find that smokers are at increased risk for reoperation after single-level lumbar diskectomy.

Smoking has been associated with diminished healing rates in patients with fracture and soft tissue injury of the spine and extremities12–15 and decreased ability to heal after surgical treatment.16–18 Presumably, this diminished capacity to heal is related to derangement of the microcirculation caused by smoking.19,20 Therefore, smokers may have a reduced ability to heal the annular defect associated with disk herniation after lumbar diskectomy and thus may be susceptible to reherniation. However, this relationship has not been shown in the current literature.

Up to now, only a few studies have examined the effects of smoking after lumbar diskectomy, and no study has found an increased risk of reoperation. The largest of the studies examining smoking as a risk factor for reoperation had a patient sample size of 810 and was drawn from the SPORT data set. Two studies used data from SPORT and found no increased risk of revision diskectomy with smoking.6,7 However, although detailed data were collected from this population, the cohort included only 73 patients who had reherniation and 201 patients who were smokers. Thus, the fact that the cohort did not show a relationship between smoking and reoperation may simply be related to insufficient sample size.

Other studies have examined the effects of smoking on other surgical outcome measures. Mehta and Sharma21 examined 143 patients who had undergone microdiskectomy or microdecompression and found no statistical difference in terms of back pain, leg pain, or function between smokers and nonsmokers. However, Kerr et al,22 using the SPORT data, found that although smokers benefited from surgical treatment, they had worse functional outcomes overall.

Using the Explorys database, the authors identified 53,360 patients who had undergone single-level lumbar diskectomy. To the authors' knowledge, this is the largest study to date examining reoperation rates. The overall reoperation rate for this entire group of patients was 8.8%, which is in agreement with the reported range of 5% to 15%.1–10 The 2-year revision rate was lower, at 4.5%. After all exclusions were considered, 26,980 patients fit the criteria. The authors found that smoking increases the risk of reoperation after single-level lumbar diskectomy by almost 150% (relative risk, 2.47). These findings are important because, although nicotine dependence and smoking have been shown to be risk factors for complications of spine surgery, no study until now has shown a significant link between smoking and revision diskectomy after single-level lumbar diskectomy. These findings highlight the importance of pre-operative assessment of risk factors and add to the growing body of knowledge on the effects that these risk factors can have on surgical complications.

Revision spine surgery presents a significant cost burden to the health care system. In 2009, Ambrossi et al8 estimated the cost of the diagnosis and management of recurrent disk herniation requiring surgery at $39,836. Revision surgery also is associated with a significantly increased risk of additional complications, such as incidental durotomy and infection.23 Although this study did not compare the rates of revision diskectomy among smokers with those among former smokers, this would be a worthwhile research topic. Other studies could compare the rates of reherniation in smokers and nonsmokers who were treated nonoperatively. Although smoking cessation cannot undo all of the long-term damage caused by smoking, it would be of interest to see whether it improves the revision rate. Potentially, smoking cessation could benefit the patient by reducing the need for revision, decreasing patient morbidity, and lowering health care costs. This effect, however, is unknown.

This study was subject to limitations, some inherent to all database studies, such as coding errors or errors as a result of patient loss to follow-up. For example, a subject who initially was listed in the Explorys database as having had a lumbar diskectomy may receive care outside of the network for revision diskectomy, and this information would not be recorded. Explorys includes multiple major health care systems and insurance providers, which can help to reduce loss to follow-up compared with a single-center database, but this limitation still exists. Additionally, even with the search features offered by Explorys, there was no way to know whether reoperation occurred at the index level of the original procedure. Explorys also could not control for multilevel index surgeries. Incomplete information on each patient's smoking history was another limitation. It was impossible to know the extent of each patient's smoking history, such as quantity or length of use, or to know whether the patient had quit smoking. Consequently, it is unknown whether risk increases with increasing pack-years and/or whether smoking cessation would reduce the reoperation rate compared with the rate for current smokers. When the smoking cohort was created, the search criteria included those who had documentation of being a smoker; this did not exclude the use of other tobacco products. Likewise, the nonsmoking group excluded those who were documented smokers, but may have included patients who were current or former users of smokeless tobacco products. When comparing smokers and nonsmokers, it is possible that unknown characteristics of the smoking group could have led to differences in rates of re-operation, despite all efforts to control for confounding variables. Finally, the data collected from Explorys may not reflect the true demographic data of all patients who undergo lumbar diskectomy. Despite these limitations, the data in this study are supported by a large sample size.

Conclusion

Smoking and nicotine dependence were associated with an almost 2.5 times increased risk of revision diskectomy within 2 years after single-level lumbar diskectomy. To date, this is the largest study showing such a significant difference. These findings contribute to the understanding of risk factors and their effects on surgical complications. Future studies are needed to assess whether smoking cessation would offer patients any benefit by reducing the overall rate of reoperation compared with current smokers as well as to examine other possible risk factors that would affect revision diskectomy rates with large patient sample sizes.

References

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Demographic Features of the Patient Groups

CharacteristicNo.

NonsmokersSmokers
Sex
  Male13,490 (63.1%)3900 (69.6%)
  Female7890 (36.9%)1700 (30.4%)
Race
  White17,590 (82.3%)5030 (89.8%)
  Black1170 (5.5%)300 (5.4%)
  Asian360 (1.7%)70 (1.3%)
  Hispanic110 (0.5%)20 (0.4%)
Authors

The authors are from Case Western Reserve University School of Medicine (EJS), Cleveland, Summa Health Medical Group (BPI), Akron, and University Hospitals (JYD, NUA), Cleveland Medical Center, Cleveland, Ohio; and the New Hampshire Spine Institute (UMA), Bedford, New Hampshire.

The authors have no relevant financial relationships to disclose.

Correspondence should be addressed to: Eric J. Smith, MD, 2622 N Moreland Blvd, Apt 19, Cleveland, OH 44120 ( ejs183@case.edu).

Received: February 01, 2019
Accepted: July 24, 2019
Posted Online: July 07, 2020

10.3928/01477447-20200619-14

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