Carpal tunnel syndrome (CTS) is the most common nerve entrapment disorder. It involves narrowing of a passage in the wrist called the carpal tunnel. This constricted tunnel presses on or pinches the median nerve and causes chronic pain in the wrist and hand.

The median nerve controls sensation in the palm side of the thumb, index finger, middle finger and part of the ring finger, as well as the impulses to some small muscles in the hand that allow the fingers and thumb to move.

The carpal tunnel receives its name from the eight bones in the wrist, called carpals, that form a structure resembling a tunnel or canal. The carpal ligament wraps around this passage. In addition to accommodating the median nerve, the carpal tunnel also contains blood vessels, connective tissue and flexor tendons, which control flexion (bending) of the fingers.

In CTS, the protective sheaths that surround each of the tendons thicken and become swollen. The swollen tendon sheaths apply increased pressure on the median nerve and produce a numbness and tingling sensation in the area of the hand where the nerve spreads out. This is the first sign of CTS.

After the initial numbness, CTS gradually progresses to a vague aching in the wrist that can extend to the hand or forearm. A person with CTS may have trouble typing on a keyboard, playing video games, knitting or performing other activities involving repetitive wrist and hand movement.

If CTS is left untreated, the pain can become progressively worse and it may result in loss of strength in the hand and wrist due to muscle wasting (atrophy). Eventually, CTS patients may have trouble differentiating between hot and cold by touch.

According to the U.S. Department of Health and Human Services, permanent damage occurs in about 1 percent of patients with CTS. However, with proper treatment, most patients can relieve the pain and numbness and restore normal use of their wrists and hands.

CTS affects up to 10 percent of the population and is more common in women than men, according to the American Academy of Orthopaedic Surgeons. It rarely affects children.