Wrist splints are common sights. You see them on cashiers and typists, on hairdressers and bank tellers. They reflect the frequency of a problem called carpal tunnel syndrome. The carpal tunnel is an anatomical structure inside the palm of the hand at its base, and the syndrome is a collection of symptoms related to the nerve that passes through the tunnel on its way from the forearm to the hand.  The nerve is the median nerve, and it is accompanied by nine tendons that connect the muscles of the forearm to the fingers.   At times, lack of space puts pressure on the median nerve, causing aching pain in the wrist, forearm and even upper arm, and numbness or tingling in the thumb, index, third and the half of the ring finger closest to the thumb. With enough pressure the thumb muscles weaken and shrink.  Any combination of these symptoms, when caused by pressure on the median nerve in the hand, adds up to carpal tunnel syndrome.

Nerves tell you they are in trouble

Pressure on nerves that run close to the surface of the body slows conduction of the electrical impulses that carry sensory information about pain, temperature, position and touch. When your foot or arm “falls asleep,” the culprit is pressure on the nerves that carry sensory information. Pressure symptoms from the median nerve in the base of the hand are so common that many people experience them transiently when they grip a steering wheel tightly over a long period of time, or pound or push with the base of the hand. Instinctively, they respond to the feeling of fingers tingling or going to sleep with re-positioning or shaking of the hand. Only when pressure is sustained do nerves become damaged enough to cause the muscles they supply to weaken. The median nerve is a common site of chronic pressure because of the anatomy of the tunnel it must pass through to the hand.

Tunnel anatomy

The roof of the carpal tunnel is an arch of bones at the base of the hand.  The floor is a horizontal span of several tendons and ligaments between the bones on the thumb side and the little finger side of the hand. The bony arch changes shape with hand movements, especially with bringing the thumb across to the little finger side, flexing the wrist and extending the wrist.

Who gets carpal tunnel syndrome?

Because the carpal tunnel is smaller in women than in men, they are more frequently affected by symptoms from pressure on the median nerve, particularly during pregnancy when hands commonly swell.  Some medical conditions like heart or kidney failure, diabetes and growth hormone producing brain tumors may cause pressure to increase in the carpal tunnel. Inflammatory conditions like rheumatoid arthritis may also bring out symptoms. While carpal tunnel syndrome seems common in people whose occupations involve repetitive hand motions or hand pressure, such as hairdressers, typists, bakers, and jackhammer operators, rigorous studies do not fault the activities alone, but the activities combined with the individual anatomic structure, and with underlying medical conditions,  if present.

The reason for those wrist splints

Since the anatomy of the hand is responsible for carpal tunnel syndrome, relief comes from maximizing the space between the ligaments and bones. When symptoms begin, the first line of treatment is a splint that keeps the wrist aligned in a neutral position – neither flexed nor extended. It also keeps the thumb from falling in toward the ring finger. The splint’s design allows for use of the fingers and thumb and it can be worn during most activities. The crucial time for keeping it on is during sleep. When we sleep our hands naturally fall into a posture of wrist and finger flexion, and some people exaggerate this pose by tucking their hands beneath them, and even unconsciously clenching them.  Hand position at night often brings carpal tunnel symptoms to light, especially aching in the forearm, and tingling in all the fingers except the pinky.

Stretching the tunnel

Stretching the base of the hand during the day is also helpful. One good stretch is accomplished by  placing the hand flat on a wall at about shoulder height, turning the body perpendicular to the wall and stepping far enough away to straighten the elbow as much as possible. Then rotate the “eye” of the elbow, its inner bend, up to face the ceiling as much as possible. Hold the stretch for up to thirty seconds at a time.

Advil doesn’t change the anatomy

Anti-inflammatory drugs like Advil can help reduce swelling of tendon sheaths if the problem with the hand is related to injury or an underlying inflammatory condition like rheumatoid arthritis, but chronic use of anti-inflammatory drugs has not been shown to help typical, uncomplicated carpal tunnel syndrome.

When conservative measures fail

If conservative measures like splinting and stretching do not resolve carpal tunnel symptoms, surgery to expand the canal is generally successful. Some surgeries are performed through a small incision, using a scope and tools inserted directly onto the tunnel to cut away the connective tissue surrounding the nerve and tendons. Other cases require an open incision in the palm.

Diagnosis

Diagnosis of carpal runnel syndrome is relatively easy from the history alone. Conservative measures can be attempted without any other tests, provided that there are no underlying medical conditions suspected to be causing the symptoms. However, if conscientiously applied conservative measures fail, or if there is muscle weakness at the time of diagnosis, then a test called a nerve conduction study and electromyogram (EMG) will almost always confirm the diagnosis. The pressure on the nerve in the carpal tunnel causes a current applied to the nerve to be delayed in its passage to the hand, easily picked up in the nerve conduction study. Tiny needles that measure activity in the palm of the hand pick up signs of loss of nerve supply to muscles.  Muscle nerve loss does not respond as well to conservative measures as sensory symptoms like numbness and tingling do, so if the EMG demonstrates muscle nerve loss, surgery is usually recommended.