Three major factors predispose a patient to thrombosis: reduced or stagnant blood flow in the veins—significant stasis of blood (which may be due to lack of movement), reduced muscular calf pump effect, and obstruction to flow may occur; injury to the vein wall—venous trauma may damage the vessel walls, promoting thrombus formation; hypercoagulability of the blood—hypercoagulable states are often associated with abnormal levels of certain clotting factors, such as antithrombin III, protein C, and protein S.