CHAPTER 127
Deep Venous Thrombosis
Definition
Venous thromboembolism is a major cause of mortality and morbidity and is manifested by deep venous thrombosis (DVT) and pulmonary embolism. This chapter is limited to the discussion of DVT. DVT occurs when a fibrin clot abnormally occludes a vein in the deep venous system, predominantly in the lower extremities. The prevailing theory explaining the development of DVT is known as Virchow triad, which includes alterations in blood flow (stasis), vascular endothelial injury, and hypercoagulation disorder. The risk for development of DVT varies according to specific characteristics of the patient, the medical condition, or the surgical procedure (Table 127.1). Conditions that may increase the risk for development of DVT are advanced age, morbid obesity, varicose veins, prolonged immobility, pregnancy, malignant disease, stroke, inflammatory bowel disease, congestive heart failure, and previous DVT. Certain hereditary conditions may also predispose to development of DVT, such as deficiencies in protein C and protein S and familial thrombophilia. Acquired deficiencies of the natural anticoagulant system include antibodies directed against antiphospholipid and heterozygous factor V Leiden mutations [1].
Table 127.1
Risk Factors for Deep Venous Thrombosis
| Patient Factors | Diseases | Procedures |
| Age > 40 years Obesity Varicose veins Prolonged immobilization Pregnancy High-dose estrogen therapy Tamoxifen Bevacizumab Previous deep venous thrombosis |
Thrombophilia Antithrombin III, protein C, protein S deficiency Antiphospholipid antibody, lupus anticoagulant Malignant disease Major medical illness Trauma Spinal cord injury Paralysis |
Pelvic surgery Lower limb orthopedic surgery Neurosurgery |
Modified from Sokolof J, Knight R. Deep venous thrombosis. In Frontera WR, Silver JK, Rizzo TD Jr, eds. Essentials of Physical Medicine and Rehabilitation, 2nd ed. Philadelphia, WB Saunders, 2008.
Patients can be categorized according to their risk for development of DVT [2] on the basis of the type of surgical procedure; orthopedic patients carry the highest risk [3] (Table 127.2). It is believed that orthopedic procedures carry such a high risk for DVT because the mechanical destruction of bone marrow during most orthopedic procedures causes intravasation of marrow cells and cell fragments and elevations of plasma tissue factor [4]. Plasma tissue factor is a potent trigger of blood clotting [5] and is found in high concentrations in bone marrow and the adventitia surrounding the major blood vessels and the brain, which places neurosurgical patients at great risk for development of DVT. After neurosurgery, the incidence of DVT has been reported to be as high as 50% [6]. Risk factors that increase the rates of DVT in neurosurgery patients include intracranial surgery, malignant tumors, duration of the surgery, and presence of paresis or paralysis of the lower limbs [7]. Patients can remain in a hypercoagulable state up to 5 weeks postoperatively [8]. In addition to surgical patients, victims of orthopedic and neurologic trauma are at great risk for development of DVT, especially if long bone fracture or paralysis is sustained. Patients who suffer injury to the spinal cord are at high risk for DVT because of stasis and hypercoagulability.
Symptoms
Venous thrombosis often occurs asymptomatically. Symptoms of DVT may include ipsilateral lower extremity edema, fever, extremity warmth, and pain. Symptoms do not rule in or rule out DVT but can serve only as a trigger for further diagnostic inquiry.
Physical Examination
The classic signs of DVT are tenderness, ipsilateral swelling, and warmth. A palpable cord can sometimes be felt, which reflects a thrombosed vein. In the past, emphasis was placed on the presence of Homan sign and calf tenderness in making a clinical diagnosis of DVT; however, these physical examination findings have been found to be nonspecific with poor positive predictive values [9]. Significant asymmetric calf edema is an important sign and can be determined by taking the circumferential measurement of the calf 10 cm below the tibial tuberosity. A 3-cm difference in calf girth is considered a significant clinical difference. When it is massive, the swelling can obstruct not only venous outflow but arterial inflow, leading to phlegmasia cerulea dolens due to ischemia. Here, the leg is usually blue and painful.
Like symptoms, physical examination findings are not sensitive or specific. In more than 50% of the instances of DVT, physical examination findings are normal.
Functional Limitations
DVT rarely causes functional compromise, except calf pain during walking. Absolute bed rest is generally not indicated, and early walking is safe in patients with acute DVT and may help reduce acute symptoms [10]. However, patients should suspend their lower extremity exercise program until they are fully anticoagulated.
Diagnostic Studies
The Wells prediction rules (Table 127.3) are a group of clinical characteristics that are useful in estimating the pretest probability of DVT. High-quality evidence exists to support the validity of these rules, and their use is recommended as a practice guideline by the American Academy of Family Physicians and the American College of Physicians [11]. They are easily implemented before more definitive testing is performed on patients [12].
Table 127.3
Wells Prediction Rules: Clinical Evaluation Table for Predicting Pretest Probability of Deep Venous Thrombosis
| Clinical Characteristic | Score |
| Active cancer (treatment ongoing, within previous 6 months, or palliative) | 1 |
| Paralysis, paresis, or recent plaster immobilization of the lower extremities | 1 |
| Recently bedridden > 3 days or major surgery within 12 weeks requiring general or regional anesthesia | 1 |
| Localized tenderness along the distribution of the deep venous system | 1 |
| Entire leg swollen | 1 |
| Calf swelling 3 cm larger than asymptomatic side (measured 10 cm below tibial tuberosity) | 1 |
| Pitting edema confined to the symptomatic leg | 1 |
| Collateral superficial veins (nonvaricose) | 1 |
| Alternative diagnosis at least as likely as deep venous thrombosis | − 2 |
From Wells PS, Anderson DR, Bormanis J, et al. Value of assessment of pretest probability of deep-vein thrombosis in clinical management. Lancet 1997;350:1795-1798.
Clinical probability: low, ≤ 0; intermediate, 1-2; high, ≥ 3. In patients with symptoms in both legs, the more symptomatic side is used.
Invasive and noninvasive diagnostic tests are available to screen for DVT. These include contrast venography, compression ultrasonography, impedance plethysmography, D-dimer testing, and magnetic resonance venography.
Contrast venography is an invasive test that is considered the “gold standard” for the diagnosis of DVT and is the only test that can reliably detect DVT isolated to the calf veins, the iliac veins, and the inferior vena cava (Figs. 127.1 and 127.2). The drawbacks to venography are its technical complexity, the requirement for the use of contrast media, the risk of allergic reaction, and the patient’s discomfort. Therefore it is not recommended as an initial screening test.
Compression ultrasonography (real-time, B-mode venous) is the procedure of choice for the investigation of patients with suspected DVT. Venous ultrasonography allows direct visualization of the vein lumen. The inability to compress the lumen of the vein is the main criterion for a positive test result. Other adjunctive findings include vein distention, absence of flow, echogenic signals within the vessel lumen, and visualization of filling defects by color Doppler studies. Systematic reviews have demonstrated high sensitivities and specificities for the diagnosis of DVT in the proximal lower extremity by ultrasonography. However, sensitivities are poor for determination of the presence of calf vein thrombosis. Visualization of calf veins by ultrasonography is technically more difficult and less reliable than diagnosis of venous thrombus in the area between the trifurcation of the popliteal vein and the femoral vein in the groin.
