What is Carpal Tunnel Syndrome?
 
The carpal tunnel is a passageway in the wrist formed by the eight carpal (wrist) bones, which make up the floor and sides of the tunnel, and the transverse carpal ligament, a strong ligament stretching across the roof of the tunnel.
 
Inside the carpal tunnel are nine flexor tendons which flex (bend down) your fingers and thumb. Also running through the carpal tunnel is the median nerve, a cord about the size of a pencil containing thousands of nerve fibers supplying sensation (feeling) to your thumb, index and middle fingers, and half of the ring finger. The median nerve lies directly beneath the transverse carpal ligament and comes in contact with the ligament when bending or straightening the wrist or fingers.
 
Carpal tunnel syndrome is caused by increased pressure in the carpal tunnel resulting in compression of the median nerve. Thickening of the tendons can restrict the space within the tunnel and cause the nerve to become pressed against the ligament forming the roof of the tunnel. When the relatively soft structure of the median nerve is pushed up against the ligament, blood flow to the nerve is restricted, causing a sensation often described as "pins and needles" to the fingers. In severe or chronic cases, numbness can occur.