Current Concepts With DVT Prophylaxis
When and how should you administer prophylaxis to patients to prevent the potential complication of deep vein thrombosis (DVT) following lower extremity surgery? These authors discuss the risk factors for DVT and examine the research on whether one should provide prophylaxis.
Deep venous thrombosis (DVT) is a rare yet potentially devastating complication of foot and ankle surgery. While many DVTs may remain subclinical or asymptomatic, DVT is a risk factor for a potentially fatal pulmonary embolism.
The majority of the research on DVT after surgery is based on patients who have undergone knee or hip arthroplasty. The published rate of DVT after these procedures ranges from 45 to 84 percent without prophylaxis.1 Only recently have there been more in-depth studies on the rates of DVT in foot and ankle surgery.
In order to appropriately manage the risks and benefits of DVT prophylaxis in patients undergoing foot and ankle surgery, surgeons must be aware of the pathophysiology of deep vein thrombosis, the risks of DVT for the proposed surgery, the risk of complications from anticoagulation and the various options available for prophylaxis today. While it is important to understand treatment options, it is equally important to understand that there are wide gaps in the literature regarding DVT after foot and ankle surgery.
Deep vein thrombosis is defined as the formation of a blood clot or thrombus in a deep vein. While it may occur in any deep vein, it is most common in the veins of the lower extremity and pelvic region. When this clot dislodges and travels to the pulmonary vasculature, this then becomes a pulmonary embolism. These are collectively known as venous thromboembolism (VTE).
Key Risk Factors For DVT
Virchow’s triad of risk factors for DVT consists of vascular endothelial injury, venous stasis and the existence of a hypercoagulable state. Hypercoagulable states can include the presence of malignancy, smoking, the use of oral contraceptives or hormone replacement therapy, congestive heart failure, inflammatory bowel disease, pregnancy and obesity. Inherited hypercoagulable states also exist and include factor 5 Leiden deficiency.1
The most important risk factor for DVT, however, is a history of prior DVT. As such, it is imperative that the foot and ankle surgeon perform a thorough preoperative history that includes not only a personal history of risk factors for DVT but a family history as well. Also bear in mind that females have a higher risk of DVT than males.1
Another important arm of Virchow’s triad is venous stasis. One can minimize this during the perioperative period by using sequential compression devices on the non-operative extremity.2 During hospitalization, one may use compression devices bilaterally but use caution in the setting of peripheral vascular disease.
If permissible, early mobilization and early weightbearing may also serve to reduce venous stasis and reduce the risk of DVT.3 If patients are not immobilized at the ankle, encourage them to begin ankle range of motion as early as is surgically permissible. Whether below knee cast immobilization is a risk factor for DVT remains controversial. Some studies identify it as a risk factor and some studies do not. Reported rates of DVT in those with below knee cast immobilization range from 2.7 to 14.8 percent.4 One study on cast immobilization demonstrated a 6.3 percent rate of DVT and 1.44 percent for pulmonary embolism without prophylaxis for the conservative treatment of a tendo-Achilles rupture.4
When taking this into consideration with other risk factors, the need for prolonged immobilization may influence the surgeon’s decision on whether to initiate DVT prophylaxis in the postoperative setting.
Pertinent Insights On Diagnosing DVT
The clinical presentation of DVT may be variable. Common clinical findings include persistent or unexplainable leg swelling. The clinical concern for DVT increases when leg swelling is unilateral. Erythema may also be a presenting sign. Homans’ sign is a physical test for the presence of DVT and is considered positive if the patient has pain in the calf with passive dorsiflexion of the foot. If a clinician suspects DVT, further diagnostic workup is indicated. When one diagnostically confirms DVT, the Homans’ sign is positive in only 8 to 56 percent of patients.3
While venography has been the historic gold standard for diagnosis of venous thrombosis, it has largely been replaced by duplex venous ultrasound for day-to-day clinical practice. Researchers have reported that venous Doppler is 89 percent sensitive and 94 percent specific for DVT.3 Laboratory testing, such as D-dimer, may be a useful part of a DVT workup. However, it is most useful as a tool to rule out DVT as it lacks specificity. In a patient with unexplained shortness of breath, fever, tachycardia or dizziness, one should expand the workup to include pulmonary embolism as well. If you suspect any form of VTE, perform an immediate workup.
What Studies Reveal About The Risk Of DVT After Foot And Ankle Surgery
While the risk of DVT following major orthopedic surgery has been well studied, there are only a few studies that address the risk of DVT following foot and ankle surgery. Complicating the decision making process is the wide variability of foot and ankle surgical procedures. The majority of studies regarding prophylaxis have examined these procedures as one group, which ranges from hammertoe arthroplasty to treatment of ankle and calcaneal fractures. The wide variation of biological insult inherent to these different procedures renders the information obtained from these studies less useful to the surgeon who is deciding whether to provide prophylaxis to the patient.
One of the most common procedures in foot surgery, the chevron osteotomy for hallux abducto valgus, has undergone specific study. In a study of 100 consecutive bunion surgery patients in Austria, researchers documented a DVT rate of 4 percent using contrast venography.5 Note that all of these DVTs were asymptomatic, were not detectable on clinical exam and none progressed to pulmonary embolism. While these patients were allowed to bear weight immediately after surgery, they were in the hospital for an average of six days. Exclusion of patients with a prior DVT or history of severe varicose veins or vein surgery probably understates the risk in this patient population.
Researchers have also specifically studied the rate of DVT in patients with Achilles tendon ruptures. In a study of 1,172 patients who sustained a complete rupture of the Achilles tendon, there was a DVT rate of 0.43 percent.6 In this same study population, the rate of pulmonary embolism was 0.34 percent. The patients in this study did not routinely receive prophylaxis.
A recent study in England examined 138,841 people who underwent foot and ankle surgery, and examined the rates of DVT for various procedures.7 The DVT rate for first metatarsal osteotomy was 0.006 percent. Hindfoot fusions demonstrated a DVT rate of 0.028 percent while ankle fractures had a rate of 0.117 percent and total ankle replacements had a DVT rate of 0 percent. The study analyzed multiple risk factors but was only able to identify increasing age and the presence of “multiple comorbidities following fracture surgery” as statistically significant risk factors. The authors do not recommend routine prophylaxis for foot and ankle surgery.
Another article from 2009 analyzed 7,264 patients who underwent podiatric surgery and identified a 0.3 percent rate of VTE (DVT and pulmonary embolism).8 The authors identified three statistically significant risk factors in this study: prior history of VTE, use of hormone replacement therapy or oral contraceptives, and obesity. The authors of this study concluded that routine prophylaxis is not warranted with the possible exception of patients with two or more risk factors. These authors underscore the need for further prospective studies. At this time, there is no evidence-based consensus as to when a patient does or does not require DVT prophylaxis after foot and ankle surgery.
Weighing The Options For Prophylaxis
Options for DVT prophylaxis include both mechanical and pharmaceutical means. The simplest method of prophylaxis is early active range of motion of both the ankle and the toes. This allows the muscles of the gastroc-soleus complex as well as the deep posterior compartment of the leg to function as a musculovenous pump to minimize stasis within the deep veins of the lower extremity.
Sequential compression devices serve to mimic the action of the muscles to stimulate blood flow through the vasculature of the leg.9 These devices have comparable rates of efficacy to heparin and low molecular weight heparin while incurring very little risk to the patient. However, adherence with these devices is very difficult outside of the hospital setting. Accordingly, compression devices are largely relegated to inpatient use.
Physicians have also had patients take aspirin for the prevention of DVT after surgery although its efficacy is under debate.10 It works by irreversibly inhibiting cyclooxygenase, which, in turn, affects the production of prostaglandins and thromboxane, thus irreversibly inhibiting platelet function. While aspirin is a relatively potent antiplatelet drug, it does not affect the coagulation cascade. Aspirin may also have side effects not related to bleeding. These side effects may include erosion of the gastric lining and exacerbation of asthma in some patients with reactive airway disease. Despite these disadvantages, aspirin has the advantage of PO dosing, minimal cost and ease of availability.9,10
The heparins work by affecting the coagulation cascade directly. Heparin inhibits the action of thrombin and other clotting factors by binding to antithrombin III. Heparin (unfractionated heparin) is available in both subcutaneous and IV administrations. Intravenous dosing is usually reserved for treatment of existing thrombosis while one may use subcutaneous dosing for VTE prophylaxis. Unfractionated heparin has a higher risk of causing heparin-induced thrombocytopenia in comparison with the low molecular weight heparins. The low molecular weight heparins are in more common use than unfractionated heparin for outpatient prevention of DVT due to ease of dosing, the lack of need for monitoring and the availability of pre-packaged self-administration kits.
While heparins can reduce the occurrence of DVT and PE, they also have their own set of disadvantages. The low-molecular weight heparins will require patients to give themselves subcutaneous injections, which may be unacceptable to some patients. There is also potential for the formation of hematomas and bruising at the injection sites.2
Warfarin therapy (Coumadin, Bristol-Myers Squibb) is another form of prophylaxis, which physicians frequently employ if long-term anticoagulation is required. Warfarin is a vitamin K analogue which, when ingested, inhibits the production of the vitamin K dependent factors (II, VII, IX and X) as well as protein C and protein S.
Warfarin may allow a patient to sustain anticoagulation for years if necessary but it is not without its pitfalls. Warfarin therapy requires frequent monitoring of the patient’s international normalized ratio (INR), which is a measure of a patient’s anticoagulation status. Due to the hepatic metabolism of warfarin, it has many potential drug interactions that may render a patient overtherapeutic or undertherapeutic. An over-therapeutic INR may place a patient at high risk for adverse events due to bleeding. An undertherapeutic INR will place the patient at risk for the development of thrombosis.
Another pitfall to the use of warfarin as prophylaxis is that the action of warfarin is delayed. Warfarin use may need to stop several days before surgery and may not be effective for several days after the initial dose. This may necessitate bridge therapy with either unfractionated or low molecular weight heparin.1
In light of the wide variety of treatment options and the limited data regarding DVT prophylaxis in foot and ankle surgery, there is still significant leeway regarding the decision of whether to administer prophylaxis to a patient prior to surgery. The surgeon and patient can best make this decision jointly after a thorough discussion of the risks and benefits.
If patients have modifiable risk factors (oral contraceptive use, smoking or obesity) for VTE prior to surgery, surgery may wait until the patient has had time to undertake risk modification. Immobility is another modifiable risk factor in many patients.
When possible, early weightbearing or early mobilization protocols have the potential to reduce the risk of VTE. In regard to patients who are immobilized at the ankle, one can still educate them about active motion of the digits. When patients must be immobilized after major hindfoot surgery, the threshold for DVT prophylaxis should likely be lower although there is still no definitive data to prove this. If a patient has multiple risk factors that cannot (or will not) be modified, one may initiate DVT prophylaxis.
Again, there is no specific data on the duration of prophylactic therapy in foot and ankle surgery, but what limited data exists suggests continuing prophylaxis until the patient is mobile. The method of prophylaxis remains at the discretion of the surgeon but should take into account the risks of therapy, the willingness of the patient to adhere with the given intervention and the effectiveness of the intervention.
While DVT remains rare in the world of foot and ankle surgery, it is a serious complication that requires surgeons to evaluate every patient’s risk factors. While prevention is the primary focus of this article and should be the primary focus of the surgeon, it is important to maintain a strong clinical suspicion in patients who have a clinical presentation consistent with DVT. Early diagnosis and treatment should be the standard that all clinicians hold themselves to when confronted with any form of VTE.
Dr. Key is in private practice at Connecticut Foot and Ankle Associates in Woodbridge, Conn. He is a Fellow of the American College of Foot and Ankle Surgeons and a Clinical Instructor in the Department of Orthopaedics and Rehabilitation at the Yale University School of Medicine.
Dr. Carelock is a Chief Resident at Yale-New Haven Hospital in New Haven, Conn.
Dr. Dux is a second-year resident at Yale-New Haven Hospital in New Haven, Conn.
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