Etiology: (a) venous blood flow stagnation during surgery spinal anesthesia or general anesthesia leads to dilatation of peripheral veins and slowing down of venous flow; during surgery, the muscles of the lower limbs are completely paralyzed due to anesthesia and lose contraction function, and after surgery, the muscles of the lower limbs are in a relaxed state due to incision pain and other reasons, resulting in blood flow stagnation and inducing deep vein thrombosis of the lower limbs. (B) damage to the vein wall 1, chemical injury intravenous injection of various irritant solutions and hypertonic solutions, such as various antibiotics, organic iodine solution, hypertonic glucose solution, etc. can stimulate the venous lining to varying degrees, leading to phlebitis and venous thrombosis. 2.Mechanical injury Local contusion, laceration or fracture fragment trauma of veins can produce venous thrombosis. Fracture of the femoral neck can damage the common femoral vein, and fracture of the pelvis can often damage the common iliac vein or its branches, which can be complicated by the formation of iliofemoral vein thrombosis. 3, infectious injury septic thrombophlebitis caused by perivenous foci of infection, less common, such as infectious endometritis, can cause septic thrombophlebitis of uterine veins. (C) blood hypercoagulability This is one of the basic factors causing venous thrombosis. Various major surgeries are the most common cause of hypercoagulable state. Intraoperative and postoperative platelet adhesions are enhanced due to tissue damage; postoperative serum levels of inhibitors of both pre-fibrinolytic activators and fibrinolytic enzymes are increased, resulting in reduced fibrinolysis. The two main causes of venous thrombosis are stagnant venous blood flow and hypercoagulable blood. A single factor does not yet cause the disease independently, but often a combination of two or three factors causes deep vein thrombosis. Symptoms: The most common main clinical manifestation is the sudden swelling of one limb. In patients with lower extremity DVT, localized pain is felt and worsens when walking. In mild cases, the localized heaviness is only felt, and the symptoms worsen when standing. Physical examination has the following features: ① Swelling of the affected limb. The degree of development of swelling is reliable only if it is accurately measured daily with a tape measure and compared with the thickness of the healthy lower extremity, which is not reliable by visual observation alone. This sign is of high value to confirm the diagnosis of deep vein thrombosis, and when the swelling of the lower leg is severe, it often leads to increased tissue tension; ② pressure pain. There is often pressure pain at the site of venous thrombosis. Therefore, the lower limbs should be examined for calf muscles, N fossa, adductor canal and femoral vein below the groin; ③Homans sign. When the foot is sharply bent to the dorsal side, it can cause pain in the deep calf muscle. Homans’ sign is often positive in case of deep calf vein thrombosis. This is caused by the passive elongation of gastrocnemius and flounder muscles, which stimulates the thrombosed veins in the calf; ④ Superficial varicose veins. Deep vein obstruction can cause elevated superficial venous pressure, and superficial varicose veins can occur 1 or 2 weeks after onset.