There are three main reasons for the swelling of one ankle: firstly, soft tissue injury in the ankle, mostly due to strain or sprain caused by excessive walking or strenuous exercise, which will lead to inflammatory edema and swelling of stasis. The second condition is due to vascular problems, such as deep vein thrombosis and vascular compression, which can lead to poor venous return, resulting in swelling of the ankle due to venous blood collection. The third condition is lymphatic reflux obstruction, mainly due to congenital lymphatic insufficiency, or lymphatic dissection after radiotherapy or surgery, and also due to infection in the lymphatic area, which will lead to lymphatic reflux obstruction over time and therefore swelling in the ankle joint.