1)  Definition:  pain and paresthesia (tingling, burning, and numbness) in the hand in the area of distribution of the median nerve (a nerve which travels through the arm to supply muscles in the forearm and hand and sensation in the hand;  visualized by the orange fiery area on the picture above), caused by compression of the median nerve by fibers of the transverse carpal ligament (a strong fibrous ligament which runs across the junction of the palm and wrist beneath the skin).

- The carpal tunnel is an anatomical passageway for several tendons and a nerve located in the wrist, and if swelling is present in the tunnel, there is decreased space for the tunnel's contents, and compression of the median nerve may occur.

- Nerves are sensitive to pressure changes, and continuous compression over time can cause nerve damage.  Carpal Tunnel Syndrome (CTS) is the most common nerve compression disorder, occurring in 1-5% of the general population.

-  Increased pressure in the carpal tunnel causes decreased blood flow to the median nerve, resulting in a lack of oxygen and nutrients which causes problems with normal nerve conduction.

-  CTS can not only lead to considerable discomfort in the hands, if it is present for long periods of time, the nerve compression can lead to impaired hand function and permanent disability.

- CTS is more common in women in or beyond middle life.

Below you see an MRI image of the wrist as if it was cut in cross section:
 

Below the same image is labeled:  B stands for wrist bones, the orange area is the carpal tunnel where the tendons and median nerve are located.
 

- This anatomic tunnel is bounded by the wrist bones on one side and the inelastic Transverse Carpal Ligament on the other.  Several tendons and the median nerve run from the forearm to the hand through this tunnel.  When swelling is present in the tunnel due to any of the various causes listed in the next section, the increased pressure on the nerve may cause the symptoms of Carpal Tunnel Syndrome.

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