Carpal tunnel syndrome is a common disorder that causes pain and interferes with the use of the hand. It is caused by pressure on the median nerve as the nerve passes through a canal formed by the bones and ligaments in the wrist. This canal is known as the carpal tunnel. A variety of conditions can cause the carpal tunnel to narrow and put pressure on the median nerve. These include injuries, such as wrist fractures; arthritis complicated by swelling of the tendons in the carpal tunnel; pregnancy, which may cause the synovium (membrane) around the tendons to thicken; and glandular abnormalities, such as diabetes and thyroid disorders. Repetitive wrist motions also may cause the disorder.