Tendons are bands of connective tissue. The tough, which often connects muscles to bones. that sends the power of the muscles to the contraction of the bones The ligaments in the hand are covered and protected by a membrane-covered sheath called the synovium. When these sheaths become inflamed, swell, they thicken and cause pain. De Quervain's Tenosynovitis, or stenosing tenosynovitis, is an blistering of the sheath surrounding the tendons of certain muscles in the hand. These muscles work to stretch the thumb at the wrist joint. The disease is ten times more common in women than men, occurs between the ages of 30 and 50, and can be associated with rheumatoid arthritis.