"Tenosynovitis" is the medical term for inflammation of the tendon sheath. It is also sometimes referred to as "tendonitis." This condition occurs when the sheath that surrounds and protects the tendon becomes inflamed, leading to swelpng, pain, and difficulty moving the affected pmb or joint. Tenosynovitis can be caused by a variety of factors, including repetitive strain injuries, acute trauma, and certain medical conditions. Treatment may involve rest, physical therapy, medications to reduce inflammation, and, in some cases, surgery.