The swelling and numbness of legs below the knee may be caused by lower extremity venous thrombosis, peripheral neuritis, lumbar intervertebral disc herniation and so on. 1. Lower extremity venous thrombosis: If the patient suffers from severe trauma, long-term bed rest, limb braking, endothelial injury, etc., it will cause lower extremity venous thrombosis, which will lead to swelling and numbness of legs below the knee, accompanied by sudden unilateral limb swelling. 2. Peripheral neuritis: If affected by drugs, chemicals, alcoholism, metabolic disorders and other factors, resulting in the patient’s legs below the knee swelling and numbness, accompanied by motor and autonomic dysfunction and other symptoms. 3. Herniated lumbar intervertebral discs: If there is injury, pregnancy, heredity and congenital developmental abnormalities and other factors, resulting in rupture of the intervertebral discs of the patient, the patient appears to have swelling and numbness of the legs below the knees, and at the same time, there will be radiating pain in the lower limbs, weakness and other symptoms. It is recommended that the patient go to the regular hospital in time, under the guidance of the doctor, to carry out a detailed examination, according to the results of the examination, and actively cooperate with the treatment.