The median nerve controls the sensations of our fingers and hands (“Carpus” is Latin for wrist). It passes through our wrists in a “tunnel”. The walls of the tunnel are formed by our wrist bones and ligaments. Also in this tunnel are the tendons that mechanically control our finger motion.
These tendons are designed to move in a straight line. If we constantly move our fingers (eg. type) with our wrists bent, the tendons rub and start to swell. Eventually, the swelling leaves no room for the median nerve. It becomes damaged by the compression and you lose sensation and strength in your hands.
Corrective action is first, a wrist brace to keep the wrist straight, next, drugs, such as cortisone, to reduce the swelling, and finally surgery, to open up the carpal tunnel and make more room. Part of the prevention is proper keyboard and seat height.