This symptom of swelling of the back of one foot may be caused by acute trauma, lower limb vascular lesions, etc., as follows: First, acute trauma: some patients suffer from acute trauma to one side of the foot, which in turn leads to local swelling. After the patient’s side of the foot is crushed and injured by heavy objects, it may lead to a series of damages such as fracture, dislocation and tendon injury, after which the patient will rapidly develop foot swelling. As the soft tissue of the foot is thin, so when swelling appears, it will be very obvious. Second, lower limb vascular lesions: Some patients may develop such symptoms secondary to vascular lesions in one lower limb. In case of deep vein thrombosis in one lower extremity, it may lead to obstruction of blood return, which in turn causes very obvious swelling in the distal part of the lower extremity, i.e. the foot.