Background: Pelvic and acetabular fractures are major orthopaedic injuries, which are known to have high rates of life-threatening venous thromboembolism (VTE) following surgery. Current guidelines recommend that thromboprophylaxis be prescribed for patients requiring major orthopaedic surgery for up to 35 days; however, the duration of hypercoagulability and increased VTE risk for pelvic and acetabular fractures is unknown. This population continues to have high rates of VTE, with a 12% incidence despite thromboprophylaxis.
Thrombelastography (TEG) is a whole-blood viscoelastic point-of-care assay which provides an overview of the entire clotting process, from clot formation to clot breakdown. The maximal amplitude (MA) parameter from TEG analysis is a measure of clot strength, and values ≥ 65 mm can be used to quantify hypercoagulability and increased VTE risk in patients after major orthopaedic injuries.
Purpose: The purpose of this study was to use serial TEG analysis to quantify the duration of post-operative hypercoagulability and increased VTE risk for patients with pelvic and acetabular fractures.
Methods: Serial TEG analysis was performed in a cohort of adult patients with surgically managed pelvic and acetabular fractures, beginning upon hospital admission until three months post-operatively, at timepoints determined a priori. Hypercoagulability was defined as MA ≥ 65 mm. Patient characteristics, including demographics and medical comorbidities, injury and surgical characteristics including fracture type, surgical treatment type, resuscitation strategies, and complications such as VTE events were captured. Patient mobility was measured using the Timed-Up-and-Go test, which was assessed by the research team. Patient-reported adherence to thromboprophylaxis was recorded by survey questions. All patients received standardized thromboprophylaxis using low molecular weight heparin (LMWH) for a minimum of 28 days. A study related compression ultrasound (CUS) was performed on POD3 as well as at 2-, 4-, and 6-week timepoints if individuals were still admitted in hospital, to capture asymptomatic proximal DVT. One- and two-sided t-tests were used to compare individual, and group mean MA values to each other as well as to the hypercoagulable threshold (MA ≥ 65 mm). Exploratory analysis with additional t-tests was used to identify risk factors for hypercoagulability over time in this population. An exploratory multivariate logistic regression model was created to predict VTE events.
Results: In total, 30 patients (22 males) with a median age of 52.5 years old (IQR = 33 – 60.8) were enrolled in this study. Serial TEG analysis demonstrated a hypercoagulable state (MA ≥ 65 mm) by post-operative day three, suggesting early increased VTE risk. Hypercoagulability peaked for patients on post-operative day seven, followed by prolonged hypercoagulability, with the majority of patients (68.8%) remaining hypercoagulable four weeks post-operatively when thromboprophylaxis was discontinued. At six weeks post-operatively, 28.6% of participants were hypercoagulable, and 22.7% remained hypercoagulable three months post-operatively, demonstrating the prolonged hypercoagulability and increased VTE risk that occurs in this high-risk population.
There were seven patients (23.3%) from the cohort who developed VTE, with five events being symptomatic pulmonary embolism (PE) and two being proximal deep vein thrombosis (DVT). Every VTE event that occurred in patients with acetabular fractures were PE, whereas two of the three patients with pelvic fractures (66.7%) had DVT only. At every timepoint, patients with acetabular fractures had higher mean MA values compared to pelvic fractures, although the difference between these groups were only statistically significant at POD5 (p = 0.044). Additionally, follow-up mobility assessments demonstrated that less mobile patients at four and six weeks post-operatively were more likely to be hypercoagulable.
The additional exploratory t-test analysis highlighted that the need for a blood transfusion, more complex acetabular fracture type, increased duration of surgery, and longer time between injury and surgery, were potential predictors for elevated MA. The exploratory logistic regression model indicated that as time between injury and surgery increased as well as increasing age, so did the likelihood of a VTE event. Additionally, male sex, the need for a blood transfusion, an anterior approach for surgical fixation, a longer time to surgery, increased use of fluids and greater age also increased the likelihood of VTE in this cohort.
Conclusion: The high VTE rate of 23.3% in this study, despite thromboprophylaxis with LMWH, highlights that prolonged hypercoagulability and increased VTE risk remains a clinical concern for patients with pelvic and acetabular fractures. Therefore, this data supports that a minimum of 35 days of post-operative thromboprophylaxis is recommended for pelvic and acetabular fractures. This duration may need to be further extended for acetabular fractures as their VTE event rate appears to be higher.
Additionally, the use of pre-operative thromboprophylaxis, screening CUS, and further investigation into alternative thromboprophylaxis agents may improve outcomes for some patients. The increased VTE risk, especially with complex acetabular fractures and reduced post-operative mobility, is critical to be aware of, in order to mitigate complications for these patients. These results support continued research to inform optimal type and duration of thromboprophylaxis for this high-risk trauma population