Abstract
Study Design
Retrospective cohort study
Objective
The purpose of this study was to evaluate safety in lumbar spinal fusion with tranexamic acid (TXA) utilization in patients using marijuana.
Methods
This was a retrospective cohort study involving a single surgeon’s cases of 1 to 4 level lumbar fusion procedures. Two hundred and ninety-four patients were followed for ninety days post-operatively. Consecutive patients were self-reported for daily marijuana use (n = 146) and compared to a similar cohort of patients who denied usage of marijuana (n = 146). Outcomes were collected, which included length of stay (LOS), estimated blood loss (EBL), post-operative myocardial infarction, seizures, deep venous thrombosis, pulmonary embolus, death, readmission, need for further surgery, infection, anaphylaxis, acute renal injury, and need for blood product transfusion.
Results
Patients in the marijuana usage cohort had similar age (58.9 years ±12.9 vs 58.7 years ±14.8, P = .903) and distribution of levels fused (P = .431) compared to the non-usage cohort. Thromboembolic events were rare in both groups (marijuana usage: 1 vs non-usage: 2). Compared to the non-usage cohort, the marijuana usage cohort had a similar average EBL (329.9 ± 298.5 mL vs 374.5 ± 363.8 mL; P = .254). Multivariate regression modeling demonstrated that neither EBL (OR 1.27, 95% CI 0.64-2.49) nor need for transfusion (OR 1.56, 95% CI 0.43-5.72) varied between cohorts. The non-usage cohort had twice the risk of prolonged LOS compared to the marijuana usage cohort (OR 2.05, 95% CI 1.15-3.63).
Conclusion
Marijuana use should not be considered a contraindication for TXA utilization in lumbar spine surgery.
Keywords: cannabis, marijuana use, spinal fusion, tranexamic acid
Introduction
In the United States, the use of recreational and medicinal marijuana has become significantly more widespread by adults of all sexes, races, and socioeconomic statuses over the past 2 decades. 1 Increasingly permissive legislatures in many states, in addition to changing societal attitudes that promote recreational marijuana use, have helped spur this increase in consumption.2,3 While multiple studies have reported that the largest increase in marijuana use has been among young adults, a considerable increase in marijuana use has also been documented in older populations.1,4 Given this, it is ever more prudent to investigate and define the effects marijuana use may have on common practices within spine surgery.
While there is considerable research on the effects of marijuana misuse on psychiatric conditions and co-substance use, the impact of marijuana on spine surgery has not been extensively studied.5,6 A recent study indicated that patients who use marijuana daily have similar rates of post-operative complications, functional outcome scores, and radiological evidence of fusion following transformational lumbar interbody fusion compared to patients who do not use marijuana. 7 However, patients who use marijuana and undergo primary total knee arthroplasty have been reported to have higher rates of complications resulting in higher rates of readmission and hospital costs. 8
Due to these discrepancies within the orthopaedic literature regarding post-operative complications in patients who use marijuana, further investigation is warranted. In particular, investigation of the effect of marijuana use on intraoperative blood loss is important to establish. There is evidence in the basic science literature suggesting that marijuana causes anticoagulant effects and limits platelet aggregation.9,10 However, tranexamic acid (TXA) is routinely used in spine surgery to limit blood loss without evidence of increased risk of thromboembolic complications. 11 The use of TXA in patients undergoing spine surgery who also use marijuana remains unexplored. Given the widespread use of TXA in patients undergoing lumbar fusion, it is necessary to clearly delineate if TXA affects patient safety among those who use marijuana prior to spine surgery.
The purpose of this study was to retrospectively compare blood loss and risk of transfusion following lumbar fusion with TXA utilization between patients who use marijuana daily and patients who do not use marijuana. A secondary objective was to also compare risk of perioperative complications. Considering the recent literature, we hypothesize that patients who use marijuana have higher mean blood loss and greater risk of transfusion compared to non-users who undergo lumbar spinal fusion with adjunct use of TXA.
Methods
Patient Selection
Two hundred and ninety-four patients who underwent 1 to 4 level lumbar fusions by one of the senior authors (AMJ) between January 2017 and February 2020 comprised the cohort for retrospective analysis. Approval was obtained for this investigation through the operating surgeon’s institutional review board. The procedures performed on each patient included open posterolateral fusion, open transforaminal lumbar interbody fusion, minimally invasive transforaminal lumbar interbody fusion, lateral interbody fusion with posterolateral fusion, or anterior interbody fusion with posterolateral fusion. No patient had the use of recombinant human bone morphogenetic protein-2 (rhBMP-2). No patient had a prior history of myocardial infarction (MI), cardiac or vascular stenting procedures, deep venous thrombosis (DVT), pulmonary embolus (PE), renal failure, or epilepsy.
Patients with daily marijuana use were selected on a consecutive basis and matched one-to-one with patients who underwent a similar procedure during the study period on a non-consecutive basis. Patients involved in trauma requiring surgical intervention, patients with malignancy or undergoing treatment for malignancy with or without spine involvement, or patients with prior lumbar procedures were eliminated from consideration for this study. All patients included in this study denied nicotine usage. Patients previously placed (preoperatively) on anticoagulation, including aspirin, were excluded from this study. No patients were placed on pharmacologic anticoagulation post-operatively for at least 90 days unless they had a DVT, PE, or cardiac event that required it. Every patient had a 10 mg/kg preload bolus of TXA given within 30 minutes prior to incision.
Patients in the marijuana cohort admitted to marijuana use at each of their preoperative visits and post-operative visits. Any patient who either started or ceased usage was no longer included in the study. Marijuana usage was defined as smoking or ingesting at least once per day. While marijuana largely remains illegal according to the laws in the state where patient collection occurred, penalties for recreational use were significantly reduced in 2014 and medicinal use was approved in 2018.12,13
Statistical Analysis
Descriptive statistics are reported as means with standard deviations or as counts with percentages, as indicated. Comparative statistics were employed to investigate differences between 2 cohorts: patients who self-reported marijuana usage vs patients who did not report usage. Univariate comparisons consisted of the independent two-sample t test for continuous variables, and chi-square or Fischer’s exact tests for categorical variables. In order to control for independent variables, a multivariate logistic regression model was created to investigate independent risk factors for 4 outcomes: prolonged length of stay (LOS), 90-day readmission, excessive estimated blood loss (EBL), and transfusion. Prolonged LOS was defined as greater than 2 days, which was the median for the sample. Similarly, excessive EBL was defined as EBL greater than the median for the sample, or 300 mL.
Statistical significance was defined as a two-tailed alpha (p) < .05. To determine the appropriate sample size, a power analysis was performed with the parameters of an effect size of 10%, an alpha of .05, and a beta of .80 (80% power). The appropriate sample size required to minimize Type II error was 61 patients in each group. All statistical analyses were performed using SPSS Statistics for Macintosh (version 26.0, IBM, Armonk, NY, USA).
Results
The age range of patients in the sample was 29 to 88 years (59.0 ± 13.9 years). There were 115 (39.4%) females in the sample. A total of 146 (50.0%) patients self-reported marijuana usage (Table 1), among whom 53 (36.3%) consumed marijuana via inhalation, 84 (57.5%) via ingestion, and 9 (6.2%) via either inhalation or ingestion (Table 2).
Table 1.
Patient Characteristics and Perioperative Outcomes.
| Marijuana | |||
|---|---|---|---|
| Yes (n = 146) | No (n = 146) | p value | |
| Female (n, %) | 60 (41.1%) | 55 (37.7%) | .632 |
| Age (mean years, SD) | 58.9 (12.9) | 58.7 (14.8) | .903 |
| Body mass index (kg/m2) | .839 | ||
| >40 | 31 (21.2%) | 33 (22.6%) | |
| 35–39.9 | 35 (24/0%) | 39 (26.7%) | |
| 30–34.9 | 32 (21.9%) | 33 (22.6%) | |
| <30 | 48 (32.9%) | 41 (28.1%) | |
| Procedure | .435 | ||
| PSF | 2 (1.4%) | 3 (2.1%) | |
| Open TLIF | 34 (23.3%) | 35 (24.0%) | |
| MIS TLIF | 40 (27.4%) | 52 (35.6%) | |
| ALIF/PSF | 38 (26.0%) | 27 (18.5%) | |
| LLIF/PSF | 32 (21.9%) | 29 (19.9%) | |
| Levels fused (n, %) | .431 | ||
| 1 | 74 (50.7%) | 75 (51.4%) | |
| 2 | 35 (24.0%) | 33 (22.6%) | |
| 3 | 34 (23.3%) | 31 (21.2%) | |
| 4 | 13 (8.9%) | 7 (4.8%) | |
| Estimated blood loss (mean mL, SD) | 329.9 (298.5) | 374.5 (363.8) | .254 |
| Length of stay (mean days, SD) | 2.47 (1.14) | 2.92 (1.32) | .002 |
| Readmission within 90 days (n, %) | 8 (5.5%) | 8 (5.5%) | .999 |
| Complications (n, %) | |||
| Myocardial infarction | 0 | 0 | |
| Seizure | 0 | 0 | |
| Deep vein thrombosis | 1 (.7%) | 1 (.7%) | .999 |
| Pulmonary embolism | 0 | 0 | |
| Anaphylaxis | 0 | 0 | |
| Acute kidney injury | 2 (1.4%) | 1 (.7%) | .495 |
| Transfusion | 5 (3.4%) | 9 (6.2%) | .151 |
| Death | 0 | 0 | |
Abbreviations: PSF, posterolateral segmental fusion; TLIF, transforaminal lumbar interbody fusion; MIS, minimally invasive surgery; ALIF, anterior lumbar interbody fusion; LLIF, lateral lumbar interbody fusion.
Table 2.
Type of Marijuana Use.
aIncludes oral use (e.g.,, tincture) and enteral use (e.g.,, edible product).
Comparing cohorts, the average age of the marijuana usage cohort (58.9 ± 12.9 years) was similar to the non-usage cohort (58.7 ± 14.8 years; P = .903; Table 1). The proportion of females in the marijuana usage cohort (60, 41.1%) was also similar to the non-usage cohort (55, 37.7%; P = .632). Body mass index (BMI) was similar between the marijuana usage cohort (33.6 ± 7.5 kg/m2) and the non-usage cohort (33.9 ± 7.7 kg/m2; P = .678). Overall, the procedure types performed were similar between groups (P = .435). There was no difference between cohorts regarding number of levels fused (P = .431). There was no difference in fusion mass based on X-ray imaging and evaluation by one of the senior authors (AMJ).
Univariate analysis of outcomes demonstrated that the marijuana usage cohort had a similar average EBL compared to the non-usage group (329.9 ± 298.5 mL vs 374.5 ± 363.8 mL; P = .254; Table 1). Furthermore, the average LOS in the marijuana usage cohort (2.47 ± 1.14 days) was less than that of the non-usage cohort (2.92 ± 1.32 days; P = .002). The rate of 90-day readmission was equal between groups, with 8 (5.5%) in each cohort (P = .999). Post-operative complications were rare with the exception of transfusion, which occurred in 5 (3.4%) patients in the marijuana usage cohort compared to 9 (6.2%) in the non-usage cohort (P = .151). One thromboembolic event (DVT) occurred in each cohort (P = .999).
Multivariate logistic regression modeling revealed that patients in the non-usage cohort had twice the risk of prolonged LOS compared to the marijuana usage cohort (odds ratio [OR] 2.05, 95% confidence interval [CI] 1.15-3.63; Table 3). Independent of marijuana usage, risk of prolonged LOS was less in patients with one-level fusion (OR .08, 95% CI 0.02-.32). Compared to the marijuana usage cohort, the non-usage cohort did not differ regarding risk of 90-day readmission (OR .87, 95% CI 0.29-2.61), excessive EBL (OR 1.27, 95% CI 0.64-2.49), or transfusion (OR 1.56, 95% CI 0.43-5.72). Risk of excessive EBL was associated with BMI >40 kg/m2 (OR 2.76, 95% CI 1.06-7.17) and BMI 30-34.9 (OR 3.18, 95% CI 1.24-8.16). One-level fusion independently conferred lesser risk of excessive EBL (OR .09, 95% CI 0.01-.55), lesser risk of prolonged LOS (OR .08, 95% CI 0.02-.32), as well as lesser risk of transfusion (OR .06, 95% CI 0.01-.61). Among the other independent variables controlled for within the multivariate model, none significantly affected risk of any of the 4 outcomes with the exception of procedure type. Compared to lateral lumbar interbody fusion with posterolateral fusion, all other procedure types conferred significantly increased risk of prolonged LOS and excessive EBL.
Table 3.
Adjusted Risk* of Outcome Metrics.
| Prolonged LOS a | Readmission | Excessive EBL b | Transfusion | |
|---|---|---|---|---|
| Marijuana | ||||
| No | 2.05 (1.15-3.63) | .87 (.29-2.61) | 1.27 (.64-2.49) | 1.56 (.43-5.72) |
| Yes | ||||
| Sex | ||||
| Male | .67 (.37-1.19) | .49 (.16-1.52) | 1.55 (.76-3.14) | .32 (.07-1.40) |
| Female | ||||
| Age group | ||||
| ≤48 | .59 (.24-1.14) | 1.94 (.39-9.64) | .73 (.29-1.84) | .54 (.07-4.10) |
| 49–58 | 1.29 (.56-3.0) | .30 (.03-3.21) | .94 (.36-2.46) | 1.09 (.17-7.16) |
| 59–69 | 1.15 (.53-2.51) | 2.06 (.42-10.1) | .81 (.31-2.14) | .32 (.05-2.13) |
| >70 | ||||
| BMI (kg/m2) | ||||
| >40 | .87 (.39-1.93) | 3.25 (.56-18.7) | 2.76 (1.06-7.17) | 1.04 (.12-8.76) |
| 35–39.9 | .94 (.44-2.01) | .90 (.12-7.07) | 1.69 (.66-4.32) | 1.82 (.29-11.4) |
| 30–34.9 | 1.28 (.59-2.82) | 7.22 (1.28-40.9) | 3.18 (1.24-8.16) | 4.47 (.71-28.1) |
| <30 | ||||
| Procedure | ||||
| PSF | 3.86 (.40-37.4) | NC | NC | NC |
| Open TLIF | 8.05 (3.00-21.6) | 1.66 (.41-6.70) | 121 (30-487) | NC |
| MIS TLIF | 8.00 (3.07-20.8) | .53 (.10-2.93) | 6.28 (1.82-21.5) | NC |
| ALIF/PSF | 2.43 (.93-6.36) | .23 (.02-2.24) | 4.57 (1.43-14.6) | NC |
| LLIF/PSF | ||||
| Levels fused | ||||
| 1 | .08 (.02-.32) | .61 (.10-3.65) | .09 (.01-.55) | .06 (.01-.61) |
| 2 | .30 (.08-1.18) | .52 (.08-3.42) | .25 (.04-1.65) | .13 (.01-1.30) |
| 3 | 1.90 (.44-8.16) | .93 (.15-5.93) | 2.26 (.36-14.2) | .47 (.07-3.20) |
| 4 |
Abbreviations: LOS, length of stay; EBL, estimated blood loss; BMI, body mass index; NC, not calculable due to insufficient sample size.
*Odds ratio (95% confidence interval).
aDefined as >2 days.
bDefined as >300 mL.
Discussion
While TXA and marijuana do not appear to be independent risk factors for adverse events in spine surgery,7,11 the effect of TXA utilization in spine surgery patients who chronically use marijuana remains unexplored. Our study examined if patients who underwent lumbar fusion surgery with adjunct TXA therapy were at greater risk of blood loss, transfusion, and perioperative complications as a factor of daily marijuana usage. Using a retrospective cohort design, we compared 146 patients with self-reported marijuana usage to 146 patients who denied marijuana usage. Using a multivariate logistic regression model, we determined that marijuana usage was only independently associated with lower risk of prolonged LOS. We found that excessive EBL and transfusion, risk of readmission, and complications were similar irrespective of marijuana usage.
Risk of excessive EBL and transfusion were similar between groups, indicating that chronic daily marijuana use does not affect the efficacy of TXA in lumbar spine surgery. To our knowledge, this is the first study to investigate the use of TXA in patients with chronic daily marijuana use. Despite evidence that pharmacologically active constituents of marijuana inhibit coagulation and platelet aggregation, this effect has been challenged within the literature.9,10 For example, there is evidence that delta-9-tetrahydrocannibinol can also have a pro-aggregation effect on platelets, although this effect has only been demonstrated in vitro. 14 Therefore, the results of this study suggest that chronic marijuana does not affect blood loss during elective spine surgery, and there is no increased risk of deep vein thrombosis or thromboembolic events with the concomitant use of TXA. While our study demonstrates that TXA maintains efficacy and safety in patients with a history of chronic daily marijuana use, further investigation is warranted to determine how the constituents of marijuana interact with human platelets in the setting of TXA.
The only significant difference among outcomes examined using multivariate modeling was shorter LOS among the marijuana usage group. This finding is consistent with previous spine surgery literature. 7 While post-operative pain scores were not collected in our study, a hypothesis for this finding is that patients with history of chronic marijuana use experience less post-operative pain. However, this hypothesis has been refuted in studies of orthopedic surgery patients. For example, in a study of patients who underwent total knee arthroplasty, patients with self-reported marijuana use required similar morphine milligram equivalents for post-operative pain control compared to non-usage patients. 15 Furthermore, in a study of trauma patients, chronic marijuana use was associated with higher patient-reported pain scores and higher opioid consumption compared to non-users. 16 However, both of these studies relied on patient records to determine marijuana usage, and neither study examined spine surgery patients. Further investigation is needed to determine why marijuana usage is associated with decreased LOS following spine surgery, with particular focus on post-operative pain and mobility.
BMI was associated with increased risk of excessive blood loss among patients with BMI 30-34.9 kg/m2 and >40 kg/m2. Increasing BMI is a known risk factor for increased blood loss in lumbar spine surgery.17,18 In our analysis, BMI 35-39.9 kg/m2 was not significantly associated with excessive blood loss, which is likely due to a combination of unknown factors rather than a direct effect of BMI. While BMI has been associated with increased blood loss in lumbar spine surgery with patients in the prone position due to increased intra-abdominal pressure, 19 BMI does not directly correlate to body composition. Patients with higher proportions of fat distributed to the abdomen are more likely to have higher intra-abdominal pressures intraoperatively, thus more closely correlating to increased blood loss. This variable was not tracked in our study, but it may be one of many reasons for the finding that BMI 35-39.9 kg/m2 was not significantly associated with excessive blood loss.
The orthopaedic literature presents a mixed picture regarding chronic marijuana use and risk of perioperative complications. In a recent single-center retrospective comparison of marijuana users and non-users who underwent transforaminal interbody lumbar fusion (TLIF), Jakoi et al. 7 did not appreciate any significant differences in perioperative complications with a minimum 12-month follow-up. Furthermore, overall 90-day complications were similar between marijuana users and non-users who underwent thoracolumbar or cervical fusions in analyses of the New York Statewide Planning and Research Cooperative System between 2009 and 2013.20,21 However, none of the previous studies reported on the use of TXA in the study populations.
Our study has several limitations. First, while the single surgeon design minimizes treatment variability, selection bias potentially occurred while determining surgical candidates. Second, we did not control for patient characteristics other than sex, age, and BMI. Incorporating additional patient characteristics, such as additional demographics and comorbidities, might have elicited greater differences between groups. Third, our study did not compare TXA utilization vs no TXA utilization within the marijuana usage group, which could potentially reveal subtle consequences specific to TXA utilization in this population. Next, we relied on patient-reported data regarding marijuana usage and non-usage. The retrospective nature of our study obviated the ability to confirm usage or non-usage using laboratory screening. Furthermore, we did not collect data on the volume or dosage of marijuana used, and therefore cannot make any conclusions regarding the dose-effect relationship between marijuana, TXA, and its effects on blood loss or other complications. Finally, the duration of surgery was not factored into our analysis. While other factors such as levels fused and procedure type serve as a proxy to surgery length, using duration of surgery would have been more appropriate given our investigation of factors such as blood loss and need for transfusion; however, this information was not available for our analysis.
Lumbar fusion with adjunct TXA therapy among patients who use marijuana daily does not increase bleeding risk compared to those who do not use marijuana. Findings such as this, which demonstrate a similar safety profile for patients with a history of chronic daily marijuana use compared to those who do not, are critical for practicing spine surgeons as they continue to navigate spine pathologies in patient populations with increasing proportions of marijuana use. Our findings suggest that marijuana use should not be considered a contraindication for TXA utilization in lumbar spine surgery.
Footnotes
Author’s note: Institutional review board approval was obtained for this research through the institution of lead author Andre M. Jakoi (Protocol no. 433-2881).
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding: The author(s) received no financial support for the research, authorship, and/or publication of this article.
ORCID iDs
Gregory J. Kirchner https://orcid.org/0000-0003-0959-0222
Alexander M. Lieber https://orcid.org/0000-0001-6517-4472
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