Deep vein thrombosis occurs intraoperatively or during the immediate postoperative period (11,12 and 13) when conditions fall within Virchow’s triad of a hypercoagulable state, endothelial damage, and venous stasis (14). An example of such a situation would be a patient undergoing an ankle fusion requiring cast immobilization for 8 to 10 weeks. Due to this immobilization and lack of muscle pump action to assist venous return, venous stasis may result (13,15). Dependent positioning of the foot and leg while a patient is sitting, ambulating with crutches, or using a wheelchair can further complicate venous stasis (9). The venous system becomes distended, and the endothelial walls of the deep veins are strained (16,17). Stasis can cause hemoglobin desaturation, which leads to hypoxia in the endothelial tissues (18,19). A thigh tourniquet would generally be used during surgery and could create deep vein endothelial wall damage as well (15). Direct injury to the venous endothelium during the surgery promotes platelet and fibrin adherence and activates the clotting cascades (9). Other associated risk factors will elevate the potential for development of a thrombus by causing stasis or creating a hypercoagulable environment within the venous system (Table 9.1).

A majority of proximal (femoral or iliac vein) clots are believed to originate from smaller emboli from deep calf vein valve cusps. The lumen of the vein is occluded, and an inflammatory reaction begins (9). Signs and symptoms of calf tenderness, edema, and localized increase in temperature and pain with passive dorsiflexion of the ankle will lead a clinician to suspect a DVT. However, sometimes the nidus may be asymptomatic. It may resolve spontaneously or embolize further proximally in the venous system or into the right side of the heart and into the pulmonary arteries. A ventilation/perfusion deficit will develop in the affected lung. Right-sided heart failure and death may ultimately occur from the increased vascular resistance that develops. Because a DVT may be asymptomatic, the first symptoms that a patient may experience could be those of a PE. A less morbid but still serious complication from DVT is postphlebitic syndrome. The ambulatory venous hypertension results from valve destruction and reversal of blood flow from the superficial to deep veins. This in turn causes edema, pain, hyperpigmentation of the skin, and increased potential for ulceration.

The majority of the literature on DVT prophylaxis in lower extremity surgery comes from hip fractures, hip replacement, and knee replacement. In the few studies conducted in foot and ankle surgery, the authors do not recommend routine prophylaxis for DVT. In a large study, Mizel et al (7) reported only a 0.22% occurrence of DVT and a 0.15% incidence of PE. They found long-term cast immobilization and non-weight-bearing status to be the only risk factors that increased the incidence of postoperative DVT but by only a small fraction of a percentage. The one drawback to this study is that the patients in the study did not receive routine venous Doppler ultrasound or venography studies unless a DVT was suspected based on positive clinical findings. Considering the possibility of “silent” DVTs, their results may be misleading. Solis and Saxby (8) reported on 201 patients undergoing foot and ankle surgery. No patient was given prophylaxis, and all patients were evaluated postoperatively with ultrasound regardless of symptoms. Only a 3.5% incidence of DVT was reported. Ultrasound was repeated in 1 week on the patients who developed DVT. If the clot failed to progress, then treatment was withheld. No patients required treatment. The associated risk factors were found to be rearfoot surgery without regard to immobilization, increasing age, and tourniquet time. The size of the study and potential for false negative ultrasound studies are drawbacks to the reliability of these results. Slaybaugh et al (9) reported their incidence of DVT to be 9 out of 1,821 patients in a retrospective evaluation of foot and ankle surgeries. They reported only three nonfatal PE, with symptoms of PE being the initial complaints in all three patients. Their profile of an especially high-risk patient was a late middle-age obese woman receiving estrogen therapy who was immobilized after surgery. Only 15% of the 1,821 patients reported received prophylaxis for DVT.

There are certain risk factors specific to foot and ankle surgery that should receive the attention of the surgeon making
the decision whether to prophylax. Major rearfoot and ankle procedures will typically take more than 2 hours to perform, thigh tourniquets or mid-calf tourniquets are used more frequently in rearfoot and ankle cases, and there is a longer period of non-weight-bearing and immobilization with rearfoot and ankle surgery. These patients tend to be of advanced age, and obesity is frequently seen in this patient population. These risk factors each increase the risk for DVT. On the other hand, the potential for major internal bleeding, hematoma formation at the surgery site, thrombocytopenia, and multiple potential drug interactions are things that should be taken into consideration when making a decision on prophylaxis. A thorough evaluation of the patient, the proposed surgery, postoperative recovery course, and all associated risk factors is recommended to assist with this decision.

Mechanical modalities used in DVT prophylaxis are elevation of the extremity, early ambulation, graduated compression stockings, and intermittent pneumatic compression (ICP) devices. Elevation of the leg and early ambulation have been used routinely for prevention of postoperative DVT. Graduated compression stockings have been the most commonly used mechanical agent in prophylaxis of DVT. These stockings are often combined with ICP devices to maintain the progress of venous return; however, their specific mechanism in prevention of DVT is unclear. They have an effect on prevention of stasis by reducing the diameter of the veins on average of 50% and improve valvular function. The linear velocity of blood flow of the superficial and deep veins is thereby increased (20), which results in less vein wall distension reducing the potential for endothelial wall injury. The increased velocity of venous blood flow reduces contact time with and concentration of coagulation factors. Graduated compression stockings have a positive effect on all three arms of Virchow’s triad (21). The literature has shown that there is no difference in efficacy between knee- and thigh-length stockings (22). Knee-length stockings have the advantage of higher compliance and lower cost. Compression stockings have been shown to reduce DVT risk by 60% when used as the sole treatment for DVT prophylaxis (23). The stocking is applied to the contralateral limb. Stocking therapy should be initiated before anesthesia is administered and continued until the patient is weight-bearing.