Carpal tunnel syndrome is a condition where the median nerve is compressed as it passes through a short tunnel at the wrist. This tunnel is formed by small bones (the carpal bones) underneath and on the sides and a thick ligament (transverse carpal ligament) across the top. This tunnel also houses the tendons which bend the fingers and thumb. The median nerve carries messages about touch, temperature and pain between the thumb, index, middle and ring fingers and the brain. In addition, the median nerve supplies the small muscles which control the thumb.