A tendon sheath cyst is a cystic mass near a joint, usually caused by chronic injury or degeneration of connective tissue mucus. Normally, the tendon sheath wraps around the outside of the tendon with a small amount of synovial fluid present between them. If the tendon sheath slides and rubs against the tendon frequently, the stimulation produces too much synovial fluid, which can cause the tendon sheath to protrude and manifest as a tendon sheath cyst. Overuse of a particular joint, resulting in chronic strain and localized injury, may lead to an increase in synovial fluid in the synovial cavity and the formation of a cystic herniation, known as a tendon sheath cyst. Chronic injuries may also affect the joint capsule, tendon sheaths, and ligaments, causing malnutrition of the connective tissues therein. The connective tissues gradually undergo mucous degeneration, and cystic swellings, i.e., tenosynovial cysts, may form. If a tendon sheath cyst develops, it is recommended to seek medical attention and treatment as prescribed by the doctor.