CORR Insights®: Rotational Thromboelastometry Findings Are Associated with Symptomatic Venous Thromboembolic Complications after Hip Fracture Surgery

Where Are We Now? While most orthopaedic surgeons have their thinking grounded in science, we are not above fortune telling. We are constantly trying to predict our patients’ futures. Orthopaedic journals are packed with studies that try to predict the outcomes of our patients based upon various data, whether those data derive from clinical observations, diagnostic imaging, or laboratory values. Of course, the ultimate goal of these predictions is to improve our patients’ outcomes as well as to satisfy ourselves that we have utilized everything in our means toward this end. We are constantly looking for a better crystal ball or deck of cards. This is particularly true regarding venous thromboembolism (VTE) and orthopaedic surgery, specifically with VTE and hip fracture surgery. Numerous studies have endeavored to find data that correspond with postoperative VTE in patients with hip fractures. Some of these studies have focused on the type of hip fracture and patient factors such as comorbidities [2], while other studies have focused on laboratory data. Laboratory data may be viewed as the most objective of these variables, and as such, could be the most useful since they generally are not subject to preconceptions or bias. Not surprisingly, previous research for laboratory values relevant to VTE has focused on clotting parameters, the coagulation cascade, or products of the coagulation cascade. Much of this research concerning hips has focused on hip fracture surgery or elective hip arthroplasty. The European Concerted Action on Thrombosis DVT Study reported that activated protein C resistance was associated with deep venous thrombosis (DVT) in elective hip replacement [1]. More recently Yoo et al. [9] reported a correlation between D-dimer levels and the development of DVT in patients who underwent hip arthroplasty. However, patients who undergo elective hip arthroplasty and those treated surgically for hip fracture are clearly not the same. In this month’s Clinical Orthopaedics and Related Research®, Tsantes et al. [6] analyzed a laboratory technique called rotational thromboelastometry (ROTEM) in patients with hip fractures. This technique accomplishes an overall assessment of clot formation and breakdown. ROTEM can be used to analyze several aspects of coagulation and can detect physiological states such as hypercoagulability or hyperfibrinolysis [7]. For example, ROTEM has been used to predict the bleeding risk in critically ill neonates [3]. The researchers used ROTEM analysis on 336 patients at the time that they were admitted to the hospital. The analysis was repeated on the second postoperative day, at which point the patients were believed to have achieved a pharmacological steady-state with their standardized postoperative VTE chemoprophylaxis, the low-molecular-weight heparin agent tinzaparin that was prescribed for all patients. Eleven patients (six with DVT, five with pulmonary embolism [PE]) developed symptomatic postoperative VTE that was confirmed by vascular ultrasound or CT angiography. Several abnormal ROTEM values were associated with an increased risk of symptomatic VTE, including higher preoperative maximum clot firmness, lower preoperative clot formation time, and lower postoperative clot formation time. The authors also noted an association of BMI with increased VTE risk. Based on these results, it might be possible to use ROTEM analysis to guide the choice of prophylactic treatment, whether by aggressive anticoagulation or aggressive mobilization as suggested by the authors, in these patients in order to minimize the occurrence of DVT and, more importantly, potentially fatal PE. Where Do We Need To Go? The development of a test to predict an event can run into the challenge of whether the suggested test actually predicts the event or simply confirms that the event has occurred. This is an important distinction as it determines whether any preemptive measure is warranted based upon the test results. While having laboratory tests to identify a hypercoagulable state that could lead to VTE is certainly valuable in patients with hip fractures, the practical aspects of this still need to be appreciated. For example, a plan to decrease VTE risk by aggressive anticoagulation and mobilization in a hypercoagulable patient with hip fracture would certainly be limited preoperatively since the patient cannot be over-anticoagulated for the operating room and certainly cannot mobilize well because of the hip fracture. Still, we’ve seen the occurrence of VTE preoperatively in patients with hip fracture [4]. Therefore, identifying a hypercoagulable state in these patients may simply add to the already known impetus to get these patients to the operating room as soon as possible. Postoperatively, perhaps we would more aggressively anticoagulate these patients as they would be high risk for VTE. However, this must be tempered against the usual concerns for excess bleeding. To add further complexity to the problem, simply treating these patients with more aggressive anticoagulation might not always be the answer. Interestingly, a multiinstitutional study has shown that aggressive anticoagulation may not reduce VTE risk in high-risk patients undergoing primary or revision hip or knee arthroplasty [5]. Therefore, we need a lab test that predicts (not confirms) VTE, combined with a strategy of treatment that reduces the risk of VTE occurrence in these at-risk patients with hip fractures. How Do We Get There? The next step is to confirm the value of ROTEM as a prognostic test. This would mean performing a study of patients with hip fracture that gathers ROTEM data but also tests for VTE at the same time the lab tests are performed. Since abnormal ROTEM results may be associated with DVT and/or PE, this would mean doing venous ultrasound and/or CT angiography at the same time as drawing ROTEM lab work, with the idea of demonstrating that a VTE was not already present at the time of the lab draw. Such research would clarify whether abnormal ROTEM results are prognostic for VTE, rather than simply being confirmatory for VTE. Previous data have shown that PE can present without DVT in trauma patients [8], but overall DVT seems to be more common. Therefore, it would seem reasonable to do a study in which a screening venous ultrasound is done on the patients each time that ROTEM labs are drawn. Past VTE studies have routinely employed venous ultrasound, and it would seem reasonable to do so here. Certainly, any patients symptomatic for PE would also be screened with CT angiography, and it may also seem reasonable to do CT angiography on any patients with abnormal ROTEM results. But it would be very challenging to screen all patients multiple times with CT angiography. Establishing an effective treatment strategy may be more elusive. There are a number of different anticoagulation medications to choose from that affect different parts of the coagulation cascade. As laboratory testing of coagulation becomes more sophisticated, researchers should determine whether specific anticoagulant medications are more effective than others depending upon which specific parts of the coagulation cascade go awry. It would be a nice example of two areas of basic science (the testing of coagulation along with coagulation pharmacology) catching up with each other. This may take some time, but the potential benefits are real. Clearly, more work is needed here. Fortune telling can be a tough business.