Blood clots in the legs are divided into arterial and venous thrombosis. Arterial thrombosis has no special implications for surgery, while venous thrombosis is due to the risk of dislodgement and pulmonary embolism at any time because the thrombus is still unstable, but is limited to the acute phase of venous thrombosis. In subacute or chronic venous thrombosis, the thrombus is relatively stable and the risk of thrombus dislodgement is very low, so there are generally no special restrictions on surgery. In contrast, venous thrombosis in the acute phase can be prevented by the implantation of a vena cava filter to prevent intraoperative movement or irritation that could cause thrombus dislodgement and the risk of death from pulmonary embolism. However, some minor procedures do not affect thrombus dislodgement, such as local superficial procedures that do not stimulate the movement of the lower limbs, or some invasive operations that do not trigger the risk of death from pulmonary embolism. Therefore, when there is a thrombus in the leg, it is necessary to clarify whether the thrombus is in the acute stage or to assess whether there is a risk of dislodgement during the operation before considering vena cava filter implantation to prevent the risk of pulmonary embolism caused by dislodgement of the thrombus.