The appearance of purple blood in the ankle indicates a local bleeding condition or an increase in local capillary permeability. Common causes: I. When the ankle joint is sprained, there is purple blood in the ankle joint due to the sprain of the ligament that wraps around the ankle joint, and at the same time, the blood vessels around the ligament are also sprained, and it is often accompanied by swelling and pain in the ankle joint. Second, when vitamin C deficiency occurs, due to the increased permeability and brittleness of capillaries, it is easy for blood to leak out of the blood vessels to the outside of the blood vessels, and it is also easy for purple blood to appear in the ankle joint. Third, coagulation system dysfunction diseases, such as coagulation factor Ⅻ deficiency, coagulation factor VII deficiency, etc., due to the lack of coagulation factors, coagulation dysfunction, also easy to appear purple blood in the ankle joint. Therefore, there are various reasons for the appearance of blood filaments in the ankle joint, which need to be investigated one by one.