There are many reasons for swelling of the outside of the foot and ankle, the common ones are trauma, heart failure, kidney failure and so on. 1. Trauma: due to long-term walking or joint sprains can lead to inflammatory oozing from the tissues around the ankle, causing pain and swelling. 2. Heart failure: due to weakened heart function, unable to carry out effective ejection of blood, blood reflux is limited, more blood stagnation in the venous blood vessels, resulting in swelling of the outside of the foot and ankle. 3. Kidney failure: after the kidney function decreases, the excretion of water and metabolites will be impaired, and water and sodium retention will occur, which will also lead to ankle swelling. There may be other causes of ankle swelling, such as varicose veins of the lower extremities, rheumatoid arthritis, etc., you should go to the hospital in time, improve the examination to clarify the cause of the disease, and standardize the treatment under the guidance of the doctor.