Depending on the site of venous thrombosis, various clinical manifestations may occur, which are described as follows: 1. Calf deep vein thrombosis Although the calf deep vein is the most likely site of thrombosis after surgery, it is sometimes missed. Common symptoms include pain and pressure in the calf, mild swelling or insignificant swelling in the calf, positive Homans sign, and normal superficial venous pressure. 2.Femoral vein thrombosis The vast majority of femoral vein thrombosis is secondary to deep vein thrombosis in the lower leg. However, a few femoral vein thrombosis can exist alone. The signs are pressure pain at the site of the adductor canal, the N fossa and the deep calf. Homans’ sign is positive or negative. 3.Iliofemoral vein thrombosis Most of the iliofemoral vein thrombosis is secondary to deep vein thrombosis in the lower leg, but sometimes it is primary in the iliofemoral vein or iliac vein. It is easy to occur in postpartum women, pelvic fractures, pelvic surgery and patients with advanced cancer. The lesions occur 2 to 3 times more often in the deep veins of the left lower extremity than in the right. This may be due to the longer course of the left common iliac vein and the compression of part of the left common iliac cavity by the right common iliac artery. Occasionally, it may also be due to a congenital reticular malformation at the junction of the left common iliac vein and the inferior vena cava. The onset of deep vein thrombosis in the lower extremity is rapid, with pain, tenderness, and significant swelling of the entire affected extremity within hours. Superficial varicose veins of the upper femur and the ipsilateral lower abdominal wall are present. There is significant pressure pain along the femoral triangle and the femoral adductor canal. Stiff objects can be felt in the femoral vein area and are painful to press. In severe cases, the skin color of the affected limb is cyanotic, called “femoral cyanosis”, suggesting extensive thrombosis of the deep and superficial veins of the affected limb, accompanied by arterial spasm, which sometimes can lead to venous gangrene of the limb. Systemic symptoms are generally not obvious, the temperature does not rise above 39 ℃, there may be mild tachycardia and acute discomfort and other symptoms “femoral cyanosis” is relatively rare.