Trauma patients are at high risk of deep venous thromboembolism, with the majority of patients exhibiting no symptoms. Although meta-analyses report the overall incidence of deep vein thrombosis (DVT) in trauma patients to be approximately 12%, the incidence of DVT in patients receiving no prophylaxis has been reported to be as high as 58%. Although a number of factors have been purported to increase the incidence of DVT, including long bone fractures, pelvic fractures, and head injuries, meta-analysis suggests that only spinal fractures and spinal cord injuries independently increase the incidence of DVT among trauma patients. Specifically, spinal cord injury has been shown to increase the risk of DVT threefold.

Various modalities have been used in an attempt to decrease the incidence of DVT and associated pulmonary embolism (PE) in trauma patients, including both low-dose unfractionated heparin and low-molecular-weight heparin (LMWH). Unfractionated heparin acts by binding to antithrombin III, which accelerates its ability to inactivate several molecules in the coagulation cascade, including factor Xa and thrombin. LMWH acts primarily by inhibiting factor Xa and its activity is correlated to factor Xa levels. LMWH has improved bioavailability and decreased incidence of bleeding as compared with unfractionated heparin.

Although low-dose unfractionated heparin has been shown to be very effective in reducing the incidence of DVT among patients undergoing elective surgery, a number of studies suggest that its effect in trauma patients is limited and that this intervention may not decrease the incidence of DVT in this population. In contrast, having originally been shown to decrease the incidence of DVT in patients undergoing orthopedic procedures, LMWH has been shown to be safe following trauma, and several reports suggest it is effective in reducing the occurrence of DVT and associated complications in the trauma population. One landmark study demonstrated a decrease of 30% in the incidence of DVT and a decrease of 58% in the incidence of proximal vein thrombosis with the use of LMWH. Suggested dosage for enoxaparin is 30 mg injected subcutaneously twice a day. It is important to note,
however, that a recent review of published studies examining LMWH suggests that even this therapy may not offer significant benefit, and better quality studies are required to settle this debate.