The majority of bulging pouches on the medial arch of the foot are due to tendon sheath cysts, because the medial arch of the foot is mainly the area of the ankle joint, and excessive activity has caused fluid to accumulate in the joint cavity, followed by cyst-like changes. For tendon sheath cysts, local braking and rest or pressure rubbing are usually recommended, and most of them can get relief from symptoms and even disappear. If the cyst does not shrink or disappear after symptomatic treatment, surgery can be considered. However, since the cyst is connected to the joint, there is a possibility of recurrence of the tendon sheath cyst if the triggering factors such as overwork or overactivity cannot be eliminated after surgery.