Deep vein thrombosis.
Pathophysiology Venous thrombosis is triggered by damage to vessels, stasis of blood flow, and increased coagulability, factors classically known as Virchow’s triad. One or more of these factors comes into play with advancing age, cancer, surgery, immobilization, fractures, the puerperium, paralysis, oral contraceptive and estrogen use, antiphospholipid syndrome, and inherited thrombophilia. Inherited thrombophilic conditions include deficiencies of antithrombin, protein C or protein S; factor V Leiden; hyperhomocysteinemia; and other rare conditions. About 40% to 60% of patients having a first episode of DVT have inherited thrombophilic abnormalities. The veins involved in DVT are lower limb (~85%); pelvic (~10%); and upper limb, shoulder, and cephalic (~5%). Whether calf vein thrombi cause clinically important PE is a matter of debate. Calf vein thrombi become dangerous if they propagate proximally, which occurs in about 20% of cases. Super ficial thrombophlebitis not related to varicose veins or obvious etiology (eg, an intravenous catheter) has about a 40% risk of associated DVT.