There are several possible causes of swelling in the left ankle: first, synovitis of the ankle joint. Synovitis is often caused by strain, cold, or other diseases, and should be diagnosed through relevant examinations and physical examination. Secondly, osteoarthritis, when suffering from osteoarthritis, there can be swelling of the joint, often involving large joints, and osteoarthritis can also occur in the ankle joint, which can be accompanied by pain and joint deformity and bone spur formation. Third, large osteoarthrosis, large osteoarthrosis most often occurs in the knee, finger joints and ankle joints, can appear swelling, pain, deformation of the ankle joint, it is necessary to conduct an X-ray examination for diagnosis. Fourth, rheumatoid disease, when rheumatoid involvement of the joints, can also appear swelling of the joints, and can be accompanied by pain, serious cases will have joint deformation, then the relevant blood tests and X-ray examination, for diagnosis.