The Median Nerve
The median nerve, which derives its name from its course along the midline of the forearm, travels from the elbow along this course to the center of the wrist and then into the hand.  In the hand it divides into branches that travel up both sides of the thumb, the index and long fingers, and the radial, or thumb side, of the ring finger.

The Carpal Tunnel
The carpal tunnel is a tunnel at the level of the wrist through which the median nerve travels.
Nine tendons, two for each finger and one for the thumb, also travel through this tunnel with the median nerve.  Each of these tendons is surrounded by a synovial sheath which allows good gliding of the tendons as they move the fingers.
At the base of this canal are the bones of the wrist, and the canal is completed by a strong ligament on the palm side of the wrist, the transverse carpal (wrist) ligament.  This forms an inelastic tunnel through which the structures pass.

Carpal Tunnel Syndrome
Carpal tunnel syndrome, a condition where swelling occurs at the wrist level, can be brought on by a number of things.
Although it is often associated with cumulative trauma (repetitive-stress injuries), carpal tunnel syndrome may be produced by any disease process that produces swelling at the wrist such that increased pressure in the carpal tunnel results in compression of the median nerve.
Conditions such as rheumatoid arthritis, gout, traumatic injuries such as wrist fractures or crush injuries, renal or cardiac disease that produce swelling, and pregnancy with resultant swelling in the extremities can all bring on carpal tunnel syndrome.  Sometimes nerves are more susceptible to entrapment in conditions (such as diabetes) which affect circulation to the nerve.  Thyroid disease and other metabolic conditions may also make the nerve more susceptible to this problem.

Symptoms
If the pressure increases within the carpal tunnel at the wrist, nerve function is affected.  This results in pain at the wrist, and numbness and tingling in the distribution of the median nerve in the hand.  This distribution is the thumb, index, and long fingers, and half of the ring finger.
The median nerve also supplies the thenar muscles, or the ball of the thumb, so movement of the thumb away from the palm may become weak.  Loss of sensation or feeling in the affected fingers also occurs.
The combination of weakness and a loss of feeling results in the problem of dropping objects and poor dexterity.  Patients often note that their pain worsens during sleep at night and complain of being awakened by numbness and tingling.  The exact reason for this increased pain is not certain, but may be due to the slight swelling in the extremities that occurs during the night.  Sustained activities such as holding an object for long periods, or driving, may reproduce the symptoms.

Diagnosis
Diagnosis is made according to the history and symptomatology described above.
As well, specific provocative tests the physician will do can confirm the diagnosis.  These include tapping over the nerve to assess the response, called the Tinel's sign, and eliciting a response with flexion of the wrist (Phalen's test), which increases the pressure within the carpal tunnel.  These tests will reproduce the symptoms of carpal tunnel syndrome in patients who have the condition.
Other tests may also be useful.  In the median nerve compression test, for example, the physician applies pressure to the region of the median nerve at the carpal tunnel.
Using electrodiagnostic studies, it is possible to test electrical conduction down the nerve.  Normal nerve function occurs by tiny electrical currents traveling along the nerve, and a delayed time in the travel of such current can indicate compression of the nerve.  Unfortunately, this test yields a false-negative result approximately 20 percent of the time—the individual may indeed have carpal tunnel syndrome, but because the test is not sensitive enough, it fails to pick this up.

Treatment
As with all cumulative-trauma problems, changing the repetitive activities that brought on the problem is important.  This may require decreased hours of this activity, use of a different technique, or stopping the activity all together and is the first measure used to help reduce swelling in the carpal tunnel.
Activity modification can also be combined with oral antiinflammatory medication.  Within the first three months of symptoms, a cortisone injection into the carpal tunnel may reduce swelling and often can resolve the symptoms; afterward, most patients will note at least a temporary improvement.  Such an injection also serves as an excellent diagnostic test for carpal tunnel syndrome.
A resting wrist splint should be worn at night to prevent the individual from sleeping in positions of wrist flexion or extension, both of which can increase the pressure within the carpal tunnel.

Surgery
If adequate conservative (nonsurgical) treatment has been given for a period of at least three months and there is ongoing deterioration which prevents either work or normal daily functions, then surgery to release the pressure both in the carpal tunnel and on the median nerve may be necessary.
Several techniques for carpal tunnel release exist and fall basically into two broad categories.
The standard "tried and true" open carpal tunnel release consists of an incision three to five centimeters long at the base of the palm.  This is a safe procedure with reliable results, but it must be done carefully to avoid complications.
The second type of carpal tunnel release is the endoscopic release, which requires two incisions, a small, half- to one-centimeter incision at the wrist and a one-centimeter incision in the middle of the palm.  The release of the transverse carpal ligament is done through an endoscope.  This technique requires less incision, allowing a slightly quicker recovery time, usually within the first month following surgery.
In one large study that was done, a comparison of the two techniques at three months following surgery showed no difference in the ultimate result.  However, several case reports following the endoscopic technique done by experienced surgeons have described damage to the median nerve or one of its branches or the arteries of the hand.  For this reason, a slightly greater risk accompanies endoscopic release.
At our clinic, we have many years' experience performing both techniques.  However, unless some specific reason such as unusual scarring of the skin (keloid formation) exists, it is our opinion that the open technique is safer, and preferable.

Referral for Advanced Surgical Techniques
Patients whose past carpal tunnel surgery has failed may be amenable to more-sophisticated surgical techniques.  Such failure may have resulted from either abnormal scarring or damage to the nerve at the time of surgery.  While this is rare, patients are often referred to us for ongoing pain problems of this nature.
Techniques include the placing of a small muscle flap over the nerve to cushion the nerve.  This often decreases the sensitivity and scarring and allows some "microgliding" of the nerve.
Wrapping the nerve with a vein, a new technique described only in recent years, may also improve the situation.

Healing after Surgery
After surgery, the wrist is placed in a soft dressing with a small splint for three to five days.  The dressing is then changed, a removable splint is placed by the hand therapist, and exercises are begun.  Sutures are removed at approximately seven to ten days after surgery, and therapy exercises then proceed over the next two to three weeks.
The symptoms of tingling, pain, discomfort, and nocturnal awakening generally resolve immediately.  Some of the numbness that may result from loss of nerve fibers may continue for a time and take longer to resolve.  Depending on the activities and work to which the patient needs to return, it may be one to three months before full recovery can be expected.
The patient should not return to strenuous or heavy activities too soon lest the earlier symptoms recur and are then difficult to treat.  Such early activity should therefore be carefully monitored by the physician.