Swelling of the left ankle may be related to osteoarthritis, trauma and rheumatoid diseases. 1. Osteoarthritis: If there is osteoarthritis in the left ankle, the synovial membrane inside the ankle joint, the surrounding ligaments, and the joint capsule may be stimulated by inflammation, which leads to the accumulation of fluid inside the left ankle joint, resulting in swelling of the joints and the formation of obvious swelling of the ankle joints, which is also accompanied by pain and deformity of the joints, and so on. 2. Trauma: the ligaments of the left ankle joint are damaged by pulling or fracture, the small blood vessels of the ankle joint are damaged, and the soft tissues around the ankle joint are damaged, which cause bleeding and bruising, resulting in swelling of the ankle joint, which is usually accompanied by pain. 3. Rheumatoid diseases: Rheumatoid diseases attack many joints in the whole body. When suffering from rheumatoid diseases, if the left ankle joint is attacked, it may lead to swelling of the ankle joint, accompanied by pain, and the joints may become deformed if the condition is serious. Swelling of the left ankle may also have other causes, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.