CHAPTER OUTLINE
Key Points 390
Pathogenesis 390
Epidemiology 391
Prophylactic Regimens after Total Hip Arthroplasty 391
Chemoprophylactic Regimens 392
Warfarin 392
Unfractionated Heparin 393
Low-Molecular-Weight Heparins 393
Fondaparinux 394
Aspirin 395
Mechanical Prophylaxis 395
The Effects of Regional Anesthesia on Thrombogenesis 396
Duration of Thromboprophylaxis 396
Prophylaxis for the High-Risk Patient 397
Postoperative Screening for Deep Venous Thrombosis 397
Recommendations 397
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Patients are at high risk for developing thromboembolic complications following total hip arthroplasty and subsequently require prophylaxis.
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Dose-adjusted warfarin, low-molecular-weight heparins, and fondaparinux are each effective in reducing the risk of thromobembolic events following total-hip arthroplasty.
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While the exact duration of chemoprophylaxis is unknown, existing data supports the use of these agents for at least 10 to 14 days.
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Patients at high risk for thromboembolic events should receive aggressive extended-duration prophylaxis.
Total hip arthroplasty (THA) is one of the most commonly performed surgical procedures in North America and has proven to be highly reliable in relieving pain, restoring function, and improving quality of life. However, patients undergoing hip replacement are at increased risk for developing venous thromboembolic disease, a potentially life-threatening complication associated with lower extremity arthroplasty. Although there is consensus among orthopedic surgeons that this potential risk mandates prophylaxis against deep venous thrombosis, the optimal prophylactic regimen has not been identified. In general, selecting a prophylactic regimen involves balancing efficacy and safety, particularly bleeding. The purpose of this chapter is to provide a critical review of the current pharmacologic and mechanical strategies for thromboembolic disease prevention after THA.
PATHOGENESIS
Multiple perioperative factors place the patient undergoing THA at risk for developing lower extremity venous thrombi. Thrombogenesis can often be related to Virchow’s triad of venous stasis, endothelial injury, and hypercoagulability. Each of these risk factors is present during the sequential stages of THA. Hip dislocation and positioning of the lower extremity for canal preparation and stem insertion result in obstruction of femoral venous outflow and subsequent stasis in the lower extremity. Regional edema and decreased patient mobilization after surgery may also contribute to decreased venous return. Extremes of internal rotation during positioning of the lower extremity have the potential to compress the femoral vessels and initiate secondary endothelial injury, and heat release from the use of exothermic bone cement may cause additional damage to the endothelium. Finally, a relative hypercoagulable state can develop during THA. Blood loss during the procedure can result in reduced serum levels of antithrombin III (AT III) and inhibition of the fibrinolytic pathway. Moreover, canal preparation and stem insertion have been shown to result in increased serum levels of markers of thrombus generation including prothrombin F1.2, thrombin-antithrombin, fibrinopeptide A, and D-dimer. Collectively these data suggest that initiating events that stimulate thrombus formation arise during surgery, and therefore the true goal of any prophylactic agent is to prevent further clot formation and propagation.
EPIDEMIOLOGY
Thromboembolic disease is the most common complication after THA and is ultimately responsible for more than 50% of the postoperative mortality associated with this procedure. In the absence of prophylaxis, asymptomatic deep venous thrombosis may develop in 40% to 60% of patients and proximal thrombosis in 10% to 40% of patients after THA ( Table 53-1 ). The majority of these thrombi remain clinically silent and resolve without detection or further sequelae. However, a small number of patients undergoing THA (2% to 5%) will experience symptoms related to thromboembolic disease. Untreated thrombi have the potential to migrate proximally and in some cases embolize to the pulmonary circulation. With the shortened duration of hospital stays, symptomatic thromboembolism often manifests after discharge from the acute care setting. In one study approximately 20% of patients undergoing major joint surgery who had a negative venogram at discharge developed venous thrombosis over the subsequent 3 weeks. Other studies have suggested that although the cumulative incidence of symptomatic deep venous thrombosis was low after THA, the majority of symptomatic events (76%) occurred after hospital discharge ( Fig. 53-1A ).
Procedure | % Deep Venous Thrombosis | % Pulmonary Embolism | ||
---|---|---|---|---|
Total | Proximal | Total | Fatal | |
Total hip arthroplasty | 42-57 | 18-36 | 0.9-28 | 0.1-2.0 |
Total knee arthroplasty | 41-85 | 5-22 | 1.5-10 | 0.1-1.7 |
Hip fracture surgery | 46-60 | 23-30 | 3-11 | 2.5-7.5 |
Currently there is no reliable strategy to determine which arthroplasty patients will develop symptoms related to lower extremity thrombosis. Up to 50% of patients who developed thromboembolism after THA have no associated risk factors, underscoring the difficulty in identifying susceptible patients. Nonetheless, there are identifiable predisposing factors that have been associated with the development of symptomatic venous thromboembolism in this cohort of patients ( Table 53-2 ). The most relevant risk factors that have been associated with the development of thromboembolic disease after hip surgery include a history of prior thromboembolic disease, obesity (body mass index >25), delay in ambulation after surgery, and female gender. Factor V Leiden mutation, antiphospholipid antibody syndrome, protein C and S deficiency, and impairment of the fibrinolytic system may increase the risk of symptomatic thromboembolic disease after hip arthroplasty in some patients. The presence of genetic polymorphisms, particularly prothrombin G20210A and AT III, has been associated with increased risk of thrombosis in patients undergoing THA. However, because the overall rate of thrombophilic disorders in the general population is low, preoperative genetic screening for THA patients has not been recommended.
Risk Factors |
Prior thromboembolic disease |
Obesity |
Female gender |
Delayed ambulation after surgery |
Advanced age |
Paralysis |
Malignancy |
Cardiovascular disease |
Fracture of the pelvis, hip, femur, or tibia |
Hypercoagulable states |
Antithrombin III deficiency |
Protein C or S deficiency |
Factor V Leiden deficiency |
Antiphospholipid antibody syndrome |
Dysfibrinogenemia |
PROPHYLACTIC REGIMENS AFTER TOTAL HIP ARTHROPLASTY
The markedly increased risk of thromboembolic disease after THA mandates the use of prophylaxis in the perioperative period. Although pharmacologic and mechanical approaches have been used extensively for over 30 years, there remains no consensus as to the ideal prophylactic regimen. Randomized trials are the gold standard for evaluating the efficacy of any new drug, and numerous well-designed randomized trials have been conducted to evaluate the efficacy of various prophylactic regimens. In general, these investigations have employed venography as a surrogate outcome measure. It is questionable whether or not these asymptomatic clots in the calf are clinically relevant. Is it a fair tradeoff to have a lower rate of asymptomatic distal calf clot formation with a new drug regimen, but a higher rate of bleeding? Ideally, the focus should be on proximal clots and symptomatic deep venous thrombosis and pulmonary embolism.
CHEMOPROPHYLACTIC REGIMENS
Various targets for anticoagulant drugs are outlined in Figure 53-2 .
Warfarin
Warfarin remains the most commonly used agent in North America after THA. Warfarin exerts its anticoagulant effect by inhibiting the vitamin K–dependent carboxylation of clotting factors II, VII, IX, and X, as well as protein C and protein S. Warfarin has been demonstrated to decrease the prevalence of deep venous thrombosis in THA by approximately 60% and proximal venous thrombosis by 70% when compared with prevalence in patients who had not received prophylaxis. Warfarin’s primary advantages over other prophylactic options are its relatively low cost and its oral route of administration. However, there are several drawbacks related to its use. Warfarin has a delayed onset of action, which may render patients relatively unprotected in the early postoperative period, at which time they may be at greatest risk for the development of thrombosis. Moreover, frequent monitoring of either the prothrombin time or international normalized ratio (INR) is required for appropriate dose adjustment. In addition, warfarin interacts with other medications, herbs, and food products as a result of its metabolism in the cytochrome P450 system of the liver. Of note, the combination of warfarin and nonsteroidal anti-inflammatory agents has been shown to result in a 13-fold increase in hemorrhagic peptic ulcers in elderly patients. Finally, warfarin has been associated with a 1% to 5% incidence of major postoperative hemorrhage after hip arthroplasty.
Warfarin’s efficacy has been compared with that of other prophylactic agents in both cohort studies and randomized clinical trials ( Table 53-3 ). A recent meta-analysis was performed on all identified randomized controlled trials from 1966 to 1998, comparing low-molecular-weight heparins, warfarin, aspirin, low-dose heparin, and pneumatic compression devices. In this review, patients receiving warfarin had the lowest incidence of proximal deep venous thrombosis (6.3%) and symptomatic pulmonary embolism (0.16%). The risk of major postoperative bleeding in patients receiving warfarin therapy was no higher than that in patients treated with placebo. Warfarin has also been compared directly with low-molecular-weight heparins in a number of randomized multicenter trials. Collectively these studies have demonstrated a similar or lower incidence of asymptomatic deep venous thrombosis in patients receiving a low-molecular-weight heparin when compared with those receiving warfarin. However, in one study the rate of major bleeding episodes was found to be higher in patients receiving a low-molecular-weight heparin.
Study | Patients | Successful Venography | Overall DVT (%) | Proximal DVT (%) | Pulmonary Embolism (%) | Major Bleeding (%) |
---|---|---|---|---|---|---|
Hull et al | ||||||
Warfarin | 388 | 363 | 10.7 | 1.0 | NA | 4.2 |
Fragmin | 388 | 354 | 24 | 3.0 | NA | 5.1 |
The RD Heparin Arthroplasty Group | ||||||
Warfarin | 218 | 174 | 11.0 | 6.0 | 0 | 4.0 |
RD Heparin | 211 | 178 | 7.0 | 3.0 | 0 | 4.0 |
Francis et al | ||||||
Warfarin | 279 | 190 | 26.0 | 8.0 | NA | 1.0 |
Dalteparin | 271 | 192 | 15.0 | 5.0 | NA | 4.0 |
Colwell et al | ||||||
Warfarin | 1495 | NA * | 3.7 | NA | 0.6 | 0.8 |
Enoxaparin | 1561 | NA * | 3.6 | NA | 0.4 | 1.2 |
Hamulyak et al | ||||||
Warfarin | 342 | 257 | 20.0 | 5.8 | NA | 2.8 |
Nadroparine | 330 | 260 | 17.0 | 6.5 | NA | 1.5 |