Anatomy of The Median Nerve
The median nerve runs into the hand to supply sensation to the
thumb, index finger, long finger, and half of the ring finger. The
nerve also supplies a branch to the muscles of the thumb, the thenar
muscles.
One of the first symptoms of carpal tunnel syndrome is numbness in
the distribution of the median nerve. This is quickly followed by
pain in the same distribution. The pain may also radiate up the arm
to the shoulder, and sometimes the neck. If the condition is allowed
to progress, weakness of the thenar muscles can occur. This results
in an inability to bring the thumb into opposition with the other
fingers and hinders one's grasp.
Looking at a cross section of the wrist allows one to visualise
the anatomy of the carpal tunnel. The carpal tunnel is an opening
into the hand that is made up of the bones of the wrist on the bottom
and the transverse carpal ligament on the top. Through this opening,
the median nerve and the flexor tendons run into the hand. The median
nerve lies just under the transverse carpal ligament.
The flexor tendons allow us to move the hand, such as when we
grasp objects. The tendons are covered by a material called
tenosynovium. The tenosynovium is very slippery, and allows the
tendons to glide against each other as the hand is used to grasp
objects. Any condition that causes irritation or inflammation of the
tendons can result in swelling and thickening of the tenosynovium. As
all of the tendons begin to swell and thicken, the pressure begins to
increase in the carpal tunnel because the bones and ligaments that
make up the tunnel are not able to stretch in response to the
swelling. Increased pressure in the carpal tunnel begins to squeeze
the median nerve against the transverse carpal ligament. Eventually,
the pressure reaches a point when the nerve can no longer function
normally. Pain and numbness in the hand begins.
There are many conditions that can result in irritation and
inflammation of the tenosynovium, and eventually cause carpal tunnel
syndrome. Different types of arthritis can cause inflammation of the
tenosynovium directly. A fracture of the wrist bones may later cause
carpal tunnel syndrome if the healed fragments result in abnormal
irritation on the flexor tendons. The key concept to remember is that
anything that causes abnormal pressure on the median nerve will
result in the symptoms of pain, numbness and weakness of carpal tunnel syndrome.
Diagnosis of Carpal Tunnel Syndrome
Physical Examination
Evaluation begins by obtaining a history of the problem, followed
by a thorough physical examination. Description of the symptoms and
the physical examination are the most important parts in the
diagnosis of carpal tunnel syndrome. Commonly, patients will complain
first of waking in the middle of the night with pain and a feeling
that the whole hand is asleep. Careful investigation usually shows
that the little finger is unaffected. This can be a key piece of
information to make the diagnosis. Other complaints include numbness
while using the hand for gripping activities, such as sweeping,
hammering, or driving. The major physical findings reflect that
pressure is increased in the carpal tunnel. If more information is
needed to make the diagnosis, electrical studies of the nerves in the
wrist may be requested. Several tests are available to see how well
the median nerve is functioning, including the nerve conduction
velocity (NCV). This test measures how fast nerve impulses are
conducted through the nerve.
Treatment Options in Carpal Tunnel Syndrome
Treatment
In the early stages of carpal tunnel syndrome, a splint will
sometimes decrease the symptoms, especially the numbness and pain
occurring at night. It may also help control the swelling of the
tenosynovium and reduce the symptoms of carpal tunnel syndrome. If
this fails to control the symptoms a cortisone injection into the
carpal tunnel may be suggested. This medication will decrease the
swelling of the tenosynovium and may give temporary relief of
symptoms.
If all of the previous treatments fail to control the symptoms of
carpal tunnel syndrome, surgery will be required to reduce the
pressure on the median nerve.
Basic Steps in Carpal Tunnel Release
A small incision, usually less than 5 cms, is made in the palm of
the hand. In some severe cases, the incision needs to be extended
into the forearm another 1cm or so. After the incision is made
through the skin, a structure called the palmar fascia is visible. An
incision is made through this material as well, so that the
constricting element, the transverse carpal ligament, can be seen.
Once the transverse carpal ligament is visible, it is cut with
either a scalpel or scissors, while making sure that the median nerve
is out of the way and protected.
Once the transverse carpal ligament is cut, the pressure is
relieved on the median nerve. Finally, the skin incision is sutured.
At the end of the procedure, only the skin incision is repaired. The
transverse carpal ligament remains open and the gap is slowly filled
by scar tissue. A bandage is applied to the hand following surgery.
This should be left in place until the first office visit after the
surgery. Sutures will be removed 10-14 days after surgery. Avoid
any heavy use of the hand for four weeks after surgery. Expect the
pain and numbness to begin to improve after surgery, but there may be tenderness in the area of the incision for several months.
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