Carpal tunnel syndrome is caused by pressure on the median nerve. The median nerve runs from the forearm through a passageway in the wrist (carpal tunnel) to the hand. It provides sensation to the palm side of the thumb and fingers, except the little finger. It also provides nerve signals to move the muscles around the base of the thumb (motor function). Anything that squeezes or irritates the median nerve in the carpal tunnel space may lead to carpal tunnel syndrome. A wrist fracture can narrow the carpal tunnel and irritate the nerve, as can the swelling and inflammation caused by rheumatoid arthritis. Many times, there is no single cause of carpal tunnel syndrome. It may be that a combination of risk factors contributes to the development of the condition.