The median nerve, which carries sensation to the thumb and first three fingers, passes through a natural passageway in the wrist. This opening - called the carpal tunnel is formed by arch-shaped wrist bones and a connecting ligament.
Various conditions, such as pregnancy, injury, arthritis and changes in the tendons caused by repetitive motion can crowd the already narrow tunnel, putting pressure on the nerve.
This added pressure can cause a tingling sensation in the fingers and the thumb and may even lead to numbness, pain and restricted movement. This combination of symptoms is called the carpal tunnel syndrome.