Swelling of the feet and ankles can occur as a result of conditions involving the local extremities as well as systemic conditions (diseases and conditions that affect the entire body). Localized processes such as injuries and infections may lead to a swollen foot and/or ankle only on the involved side. Swelling of the ankle on one side is often a result of sprains or strains.
Sometimes diseases that affect the entire body, such as heart disease and kidney or liver failure, can result in excess fluid buildup (edema) that is often concentrated in the legs and feet, leading to swelling not only of the ankles but also of the feet and lower legs. This can also occur with obstruction of the venous system, as may occur with pregnancy and obesity. Diseases of the joints, such as arthritis, can also affect the joints of the ankle and foot, leading to swelling of the involved areas. Treatments for swollen ankles and swollen feet depend on the particular cause, but anti-inflammatory medications are often used to manage the pain associated with strains and sprains.