Foot sprain for a month or swelling, may be ligament injury or tear, insufficient rest, vascular disease of the lower extremities and other reasons, as follows: First, ligament injury or tear: may be a foot sprain, there is an acute ligament injury or ligament tear. When ligament tear occurs, the recovery time is very slow, and it takes 2-3 months to effectively reduce the swelling. Second, insufficient rest: in the foot sprain did not have sufficient rest, such as no brace or plaster braking, but often walk on the ground, so that the swelling will be difficult to subside, and the swelling will come back. Third, lower extremity vascular disease: there may be lower extremity vascular disease, such as lower extremity deep varicose veins or lower extremity venous thrombosis, can cause the sprain part of the blood reflux obstruction, a large amount of blood stagnation in the ankle, will cause ankle, dorsum of the foot persistent swelling.