Your doctor has recommended that you undergo hand surgery to treat carpal tunnel syndrome. But what exactly is carpal tunnel syndrome 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 archshaped 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.