Inflammation of a tendon sheath, due to irritation of this thin, filmy tissue by overuse of the tendons, which slide within them, or to bacterial infection. It is often an occupational disease, affecting tendons used in repetitive motions on the job. The tendon becomes swollen and red, with pain that increases on motion. The swelling hampers the tendon's sliding within, causing stiffness. Treatment involves immobilization with a splint, cast, or bandage and gradually increasing motion after inflammation subsides, which may happen sooner with corticosteroid injections. Repeated episodes can permanently thicken the sheath, limiting motion.
Learn more about tendinitis with a free trial on Britannica.com.