Tendon sheath cysts are related to joint degeneration, trauma, and inflammatory stimuli. 1. Tendon sheath cysts are related to joint degeneration, for example, long-term engagement in a movement or often do tired work can occur joint strain, degeneration, tendon sheath periarticular tendon membrane secretion of fluid to form a cyst. 2. Trauma: After trauma, the local area will cause exudate reaction, which will infiltrate into the surrounding group to form a package and form a cyst. 3. Inflammatory stimulation: If there is infection around the joint, long-term inflammatory stimulation can appear tendon sheath cysts. In addition to the above reasons, there are also mucous degeneration of the tissues around the joints can also appear tendon sheath cysts, small cysts without pain do not need special treatment, if the cyst is relatively large can be surgically removed.