Abstract
Background
Several strategies exist to prevent venous thromboembolism (VTE) in operative pelvic and acetabular fractures, however literature lacks consensus on the optimal thromboprophylaxis. Even more debated, and perhaps controversial, is whether aspirin provides adequate thromboprophylaxis in the setting of these injuries. The primary objective was to evaluate the efficacy of aspirin in the prevention of venous thromboembolism (VTE) events, including deep vein thrombosis (DVT) and pulmonary embolism (PE) in operative pelvic and acetabular fractures compared to other anticoagulants.
Methods
A retrospective chart review of pelvic and acetabular fractures that underwent operative fixation was completed. The incidence of VTE and hematoma formation was evaluated and compared between patients who received aspirin versus enoxaparin or heparin. Multivariate analysis was performed to control for confounding demographic, comorbidity, and injury-related variables. The outcome measurements included development of DVT and/or PE and hematoma formation.
Results
Of patients with operative pelvic and acetabular fractures, 4.2% developed a DVT and 3.5% developed a PE, with 1.4% developing both. Of these patients 37.5% were treated with aspirin versus the 62.5% treated with heparin or enoxaparin. There was no significant difference in the incidence of DVT or PE between cohorts (p=0.498 and p=0.262). Aspirin trended toward significance as protective against post-operative hematoma (p=0.085).
Conclusion
This study suggests that aspirin is an acceptable method of VTE thromboprophylaxis with no inferior results to other common anticoagulants used in operative pelvis and acetabular fractures. As a chemoprophylactic agent, aspirin is an efficacious option in these complex injuries that shows no increase in the incidence in symptomatic VTE events.
Level of Evidence: III
Keywords: aspirin, pelvis, acetabulum, fracture, dvt/pe
Introduction
Pelvic-acetabular trauma injuries are complex, frequently require surgical intervention, and carry a high risk of complications. These can lead to poor patient outcomes and large economic health-care burdens.1,2 These fractures commonly occur with concomitant polytraumatic injuries and in the setting of significant medical comorbidities. Development of a venous thromboembolism (VTE) following surgical fixation of pelvic and acetabular fractures is a serious and sometimes life-threatening complication with significant economic implications. Previous studies have elucidated independent risk factors that predispose these patients to increased risk of pulmonary embolism (PE) and deep vein thrombosis (DVT) including age, associated injuries, injury severity, and time to surgery.3-6 One recent study in hip fracture patients demonstrated that VTE events were an independent reason for a 2-fold increase hospital length of stay and cost.7 Rates of VTE range from 10-30% and are even greater in patients who receive no chemoprophylactic treatment. Coupled with a small but significant rate of pulmonary embolism (PE) in pelvic and acetabular fractures, prevention strategies are critical.3-5,8-13
Although VTE is a known complication, there is limited data and no consensus on optimal thromboprophylactic agents and algorithms following operative fixation of operative pelvic trauma.8,14,15 With high variability among different institutions, it is often debated if aspirin is an effective thromboprophylactic agent. Although a multitude of anticoagulants are used in the prevention of VTE, the associated risk of bleeding or hematoma development is another important consideration. Despite the extensive reports on the effectiveness of various anticoagulants in total joint arthroplasty literature,16-19 very little data exists regarding these thromboprophylactic medications in the setting of fracture patients, particularly pelvic and acetabular fractures. In fact, to the author’s knowledge no studies evaluating the efficacy of aspirin compared to enoxaparin or heparin in preventing symptomatic VTE in these complicated injuries is described in the literature.
The objective of this study is to evaluate the observed incidence of symptomatic VTE following operative fixation of pelvic and acetabular fractures in patients treated with aspirin compared to the short-acting injectable anticoagulants, enoxaparin and heparin. A secondary aim was to compare the rate of other complications associated with these chemoprophylactic agents. We anticipated that aspirin would be an efficacious VTE prophylaxis agent and have a lower rate of hematoma development compared to other agents.
Methods
After institutional review board (IRB) approval, a retrospective chart review of patients who sustained pelvic ring and acetabular fractures treated with operative fixation was performed. Current Procedural Terminology (CPT) codes identified 163 pelvic or acetabular fractures managed operatively between 2015-2020 at our level 1 trauma center. Patients were included if they were ≥18 years of age, received aspirin, enoxaparin, or heparin as their primary anticoagulant, and had a minimum of 6 weeks post operative follow up, Nearly all post-operative VTE occur early within this timeframe.20,21 Patients were excluded if they were <18 years of age (4), had a pathologic fracture (2), had undergone previous operative fixation of pelvis or acetabulum (4), received warfarin or a newer oral anticoagulant (6), or lacked 6 week follow up (3).
Three fellowship-trained traumatologists treated all fractures. Surgical approach was dictated by fracture pattern and surgeon preference. The primary team determined treatment with aspirin, enoxaparin, or heparin. Patient demographics, medical comorbidities, and post-operative weight bearing status were accounted for across groups and normalized in a multivariate analysis.
The primary outcome measures were development of DVT or PE within a 6-week post-operative period. Hematoma development was considered a secondary outcome. Hematoma formation was defined by evidence on computed tomography (CT) and a drop in hemoglobin. Patients were treated with aspirin 81 milligrams (mg) twice a day, enoxaparin 40mg daily, or 5,000 units heparin twice a day. Mechanical prophylaxis of ambulation and sequential compressive devices (SCDs) were used in all patients. The rate of VTE and hematoma formation was compared between patients receiving aspirin and short-acting injectables, enoxaparin and heparin. Incidence of VTE and post-operative hematoma was evaluated between these groups.
Other variables reported to affect development of VTE were collected. Age, gender, time to surgery, type of anticoagulant, weight bearing status, past medical history including diabetes mellitus (DM), hypertension (HTN), chronic kidney disease (CKD), coronary artery disease (CAD), body mass index (BMI), smoking status, previous history of DVT, and head trauma were assessed as potential risk factors of VTE. Trauma scores such as abbreviated injury scale (AIS) and injury severity scale (ISS), intensive care unit (ICU) length of stay (LOS), hospital LOS, and ventilator time were also assessed as potential confounders. Additionally, in this study both posterior (Kocher-Langerbeck) and anterior (anterior intrapelvic, Pfannenstiel, or ilio-inguinal) approaches were used and evaluated as confounding variables.
Statistical Analysis
Categorical variables are expressed as percentages and continuous variables are expressed as mean ± standard deviation. Continuous variables were found to not be normally distributed by Kolmogorov-Smimov tests. Univariate analysis comparing incidence of confounding variables and complications was performed using Mann-Whitney U test or chi-squared/fisher’s exact tests as appropriate.
Multivariate binary logistic regression models were created for complications that were significantly different based on surgical approach on univariate analysis. Confounding variables with p<0.10 were included for analysis. An a=0.05 was considered statistically significant. Statistical analysis was performed using SPSS (SPSS 25.0, IBM, Armonk, NY).
Results
There were 144 pelvic and acetabular fractures that met inclusion criteria. Mean age was 42.2 ± 17.1 years. There were 95 males (66.0%) and 49 females (34.0%). There were 6 patients (4.2%) that developed DVT and 5 patients (3.5%) that developed PE. Two patients developed both (1.4%).
There were 54 patients treated with aspirin (37.5%) and 90 patients treated with heparin or enoxaparin (62.5%). On univariate analysis of complications, there was a significantly lower incidence of hematoma formation in the aspirin cohort (n=3, 5.6% vs. n=19, 21.1%, p =0.015) (Table 1). There were no differences in incidence of DVT, PE, or transfusion between cohorts. Similarly, there were no differences in the incidences of infection or mortality.
Table 1.
Univariate Analysis of Complications
| Complications | Enoxaparin/Heparin | Aspirin | Relative Risk | 95% Confidence Interval | P-value |
|---|---|---|---|---|---|
| Primary Complications of Interest | |||||
| Deep Vein Thrombosis | 4 (4.4%) | 2 (3.7%) | 0.935 | 0.523-1.670 | >0.999 |
| Pulmonary Embolus | 3 (3.3%) | 2 (3.7%) | 1.043 | 0.504-2.158 | >0.999 |
| Hematoma | 19 (21.1%) | 3 (5.6%) | 0.674 | 0.539-0.843 | 0.015 |
| Transfusion | 17 (18.9%) | 6 (11.1%) | 0.816 | 0.615-1.083 | 0.217 |
| Secondary Complications of Interest | |||||
| Infection | 6 (6.7%) | 3 (5.6%) | 0.933 | 0.577-1.509 | >0.999 |
| Mortality | 1 (1.1%) | 2 (3.7%) | 1.894 | 0.380-9.429 | 0.556 |
On univariate assessment of potential demographic and comorbidity confounders, the aspirin cohort was found to have a lower incidence of obesity (n=13, 24.1% vs. n=40, 46%, p=0.009) (Table 2). On univariate analysis of potential injury and perioperative confounders, the aspirin cohort was found to have lower ISS (11.0±7.9 vs. 15.6±10.4, p=0.010), lower incidence of ICU stay (n=10, 22.7% vs. n=37, 51.4%, p=0.002), less weight bearing restrictions (p=0.001), and received more heterotopic ossification prophylaxis (p=0.031)(Table 3). Furthermore, there was no difference in rate of DVT or PE based on an anterior or posterior approach (Table 3).
Table 2.
Univariate Analysis of Demographics and Comorbidities
| Potential Confounder | Enoxaparin/Heparin | Aspirin | Relative Risk | 95% Confidence Interval | P-value |
|---|---|---|---|---|---|
| Demographic | |||||
| Age | 40.2±16.0 | 45.5±18.5 | - | - | 0.127 |
| Gender | |||||
| Male | 55 (61.1%) | 40 (74.1%) | 0.550 | 0.262-1.155 | 0.112 |
| Female | 35 (38.9%) | 14 (25.9%) | |||
| Comorbidities | |||||
| Smoking | 30 (33.3%) | 26 (48.1%) | 1.273 | 0.959-1.688 | 0.077* |
| Obesity | 40 (46.0%) | 13 (24.1%) | 0.708 | 0.552-0.907 | 0.009 |
| Hypertension | 24 (26.7%) | 16 (29.6%) | 1.058 | 0.790-1.416 | 0.701 |
| Diabetes | 8 (8.9%) | 8 (14.8%) | 1.281 | 0.772-2.127 | 0.273 |
| Chronic Kidney Disease | 1 (1.1%) | 0 (0%) | - | - | >0.999 |
| Coronary Artery Disease | 2 (2.2%) | 4 (7.4%) | 1.913 | 0.613-5.973 | 0.197 |
| Prior Deep Vein Thrombosis | 0 (0%) | 1 (1.9%) | - | - | 0.375 |
Table 3.
Univariate Analysis of Injury and Perioperative Variables
| Potential Confounder | Enoxaparin/Heparin | Aspirin | Relative Risk | 95% Confidence Interval | P-value | |
|---|---|---|---|---|---|---|
| Concurrent Injuries | ||||||
| Head Injury | 5 (5.6%) | 1 (1.9%) | 0.739 | 0.505-1.082 | 0.410 | |
| Polytrauma | 51 (56.7%) | 24 (44.4%) | 0.831 | 0.642-1.077 | 0.155 | |
| Injury Severity | ||||||
| Abbreviated Injury Scale | 2.8±0.8 | 2.6±0.7 | - | - | 0.083* | |
| Injury Severity Scale | 15.6±10.4 | 11.0±7.9 | - | - | 0.010 | |
| Ventilator | 15 (20.8%) | 3 (6.8%) | 0.698 | 0.535-0.911 | 0.063* | |
| Intensive Care Unit Stay | 37 (51.4%) | 10 (22.7%) | 0.644 | 0.489-0.849 | 0.002 | |
| Perioperative Details | ||||||
| Delay ≥48 Hours from Admission | 60 (68.9%) | 40 (74.1%) | 1.097 | 0.842-1.429 | 0.508 | |
| Weight Bearing Status | As Tolerated | 5 (5.6%) | 6 (11.1%) | - | - | 0.001 |
| Partial | 43 (47.8%) | 40 (74.1%) | ||||
| Nonweight Bearing | 13 (14.4%) | 4 (7.4%) | ||||
| Transfers Only | 29 (32.2%) | 4 (7.4%) | ||||
| Heterotopic Ossification prophylaxis | Radiation | 20 (22.2%) | 21 (38.9%) | - | - | 0.031 |
| Indomethacin | 4 (4.4%) | 5 (9.3%) | ||||
| Surgical Approach | Anterior | 25 (27.8%) | 12 (22.2%) | - | - | 0.464 |
| Posterior | 35 (38.9%) | 29 (53.7%) | ||||
| Lateral | 8 (8.9%) | 4 (7.4%) | ||||
| Percutaneous | 17 (18.9%) | 8 (14.8%) | ||||
| Combined | 5 (5.6%) | 1 (1.9%) | ||||
On multivariate analysis of major complications, accounting for the confounding variables found on univariate analysis, there were no significant differences in the incidence of VTE between aspirin and enoxaparin/heparin cohorts (Table 4). However, aspirin trended on significance with less post-operative hematoma formation (adjusted odds ratio [aOR]: 0.687, 95% Confidence Interval [CI]: 0.015-1.315, [p=0.085]).
Table 4.
Multivariate Analysis of Complications Based on Anticoagulation
| Complication | Adjusted OR | 95% Confidence Interval | P-value |
|---|---|---|---|
| DVT | 3.377 | 0.100-114.506 | 0.498 |
| PE | 10.174 | 0.177-585.710 | 0.262 |
| Hematoma | 0.139 | 0.015-1.315 | 0.085 |
| Transfusion | 0.687 | 0.146-3.234 | 0.635 |
Discussion
Several strategies exist to prevent venous thromboembolism (VTE) in operative pelvic and acetabular fractures, however the current literature lacks consensus on optimal thromboprophylaxis, particularly on the use of aspirin compared to other anticoagulant agents. This study suggests that there is no significant difference in the rate of VTE with aspirin compared to short-acting injectables enoxaparin and heparin and there is a trend towards a lower rate of hematoma associated with the use of aspirin.
Development of postoperative hematoma has been associated with an increased rate of surgical site infection (SSI).22 Often patients suffering from pelvic trauma are polytraumatized patients and at high risk for complications. The reported rate of surgical site infections that occur following operative fixation of pelvic and acetabular fractures is 5-8%.23,24 The ability to limit infection and recognize factors that may be protective in these patients is critical since infection can greatly hinder the recovery of patients and add an unprecedented burden to the patient and the medical system.
Many patients with pelvic and acetabular fractures undergo a long stay in an ICU, are immobilized with weight bearing restrictions and have high ISS scores. Previous studies demonstrate that these factors are associated with increased development of VTE.6,25 In this study these variables, while noted to be lower in the aspirin cohort, were controlled for in the multivariate analysis to eliminate their confounding effect. Thus, there was no evidence to indicate that aspirin was inferior to enoxaparin or heparin. This study suggests that aspirin provides adequate VTE chemoprophylaxis following operative fixation of pelvic and acetabular fractures.
In patients with pelvic and acetabular fracture, previous studies have noted that early initiation of VTE chemoprophylaxis is a significant preventative measure,25 but its use must be balanced with the risk for bleeding and development of post-operative hematoma. With aspirin trending towards significance as protective against hematoma, this may represent a favorable option in the appropriate patients.
Additionally, there was no significant association in the risk of VTE events and the approach utilized for the pelvis or acetabulum fractures. We anticipated that the anterior approach would be a risk factor for VTE events due to mobilization and direct manipulation of great vessels that is often required. We theorized that there could be a potential risk that this could increase turbulence and thus increase the risk of a VTE event. However, this was not demonstrated in this study. Another recent study showed that this theoretical risk was not substantiated and that the rate of VTE was not increased in the anterior approach.6 Furthermore, this was a variable that was controlled for in the multivariate analysis. Regardless of approach aspirin appears to be an efficacious chemoprophylactic agent in patients with pelvic and acetabular fractures that undergo operative fixation.
Aspirin as an effective anticoagulation agent has been recognized in the total joint arthroplasty literature.19 This study suggests that it is also an effective thromboprophylactic medication in operative pelvic trauma and represents certain benefits for patients. The ease of administration compared to enoxaparin and heparin is a substantial consideration. Additionally, the relatively low cost of an over the counter medication is significant. These factors could potentially lead to increased patient compliance post-operatively.
This study is not without limitations. There are inherent limitations given the retrospective nature. Although it represents one of the larger cohorts of pelvic and acetabular fractures in the literature that reviews VTE prophylaxis, a larger population would be beneficial. With this small sample size that showed differences between groups such as less obesity, lower ISS, shorter ICU LOS and less restrictive weightbearing were analyzed using a multivariate regression model. However, a larger cohort examined prospectively would provide greater understanding of the optimal VTE prophylactic protocol. Furthermore, this study only examined aspirin compared to short-acting injectables, enoxaparin and heparin. However very few patients were excluded for receiving an alternative anticoagulation regimen for VTE prophylaxis, thus this may not be a significant limitation. While this study suggests that aspirin is not inferior to other anticoagulants, larger randomized controlled trials are necessary to further determine the optimal anticoagulation agent to reduce the risk of both VTE and postoperative hematoma formation in operative pelvic and acetabular fractures.
Conclusion
In this study, aspirin had an equivalent incidence of symptomatic VTE in operative pelvis and acetabular fractures compared to enoxaparin/heparin. This suggests that aspirin may provide an acceptable method of VTE thromboprophylaxis in operative pelvis trauma. In fact, as aspirin may reduce the incidence of post-operative hematoma, it may be potentially advantageous in reducing certain complications in patient recovery.
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