The greatest risk of deep vein thrombosis in the lower extremities is the dislodgement of the embolus leading to pulmonary embolism, which can lead to sudden death, and the inferior vena cava filter acts as an umbrella to capture some of the dislodged emboli. Placement of an inferior vena cava filter significantly reduces the incidence of pulmonary embolism. Indications for inferior vena cava filter placement: ① contraindications to anticoagulation: patients with lower extremity venous thrombosis with intracranial hemorrhage or after major surgery, etc.; ② serious complications of anticoagulation (e.g., patient bleeding, need to discontinue anticoagulation); ③ ineffective anticoagulation: recurrent acute or chronic lower extremity deep vein thrombosis despite adequate anticoagulation; ④ large pulmonary embolism despite anticoagulation; ⑤ iliofemoral vein DVT with large (more than 125px) free floating proximal segment of thrombus; (6) before surgical retrieval or thrombolysis of lower extremity DVT; (7) poor compliance with medication anticoagulation or braking bed rest, with higher risk of pulmonary embolism from dislodged thrombus.