Pain on the lateral side of the left ankle. The following diseases should be considered when this condition occurs: First, ligament injury of the ankle joint, such as frequent long-distance walking or frequent weight-bearing activities, such as hiking, hiking, and going up and down stairs, can cause ligament strain of the ankle joint, which may result in chronic pain of the inner or outer ankle. Secondly, it may be degenerative osteoarthritis of the ankle joint. This condition mostly occurs in elderly patients, as the joint cartilage keeps degenerating and losing, the cushioning force of the joint decreases, which will cause the wear and tear of the joint to increase and the stress of the joint to concentrate. As a result, chronic pain in the joints will be manifested during activity and weight bearing. Third, it may be peroneal tendonitis. The peroneal tendon is from the back of the ankle joint through the tendon groove of the outer ankle to the sole of the foot. If inflammation of the peroneal tendon occurs, it will manifest as pain at the back of the outer ankle.