How carpal tunnel syndrome works and how to treat it
I see a number of people who suffer from carpal tunnel syndrome. Carpal tunnel is a very common condition, often as a result of repetitive injury at home or in the workplace. It is one of a number of repetitive strain injuries or “RSIs.”
Carpal tunnel symptoms usually include numbness and/or pain in the hand and wrist that may extend up into the arm, shoulder or even neck. The numbness, tingling or pain frequently wakes people during sleep.
To understand the condition, it’s helpful to have a lesson in wrist anatomy (see accompanying diagram). There are eight carpal bones that make up the wrist. If you hold your wrist with your palm facing up, these bones form a U-shaped valley. The top of the valley is covered by a piece of connective tissue called the transverse carpal ligament. These structures together form the carpal tunnel.
The carpal tunnel is a very cramped space and some very important structures run through it. It houses nine flexor tendons and the median nerve. The tendons that run through the tunnel connect the muscles in the palm side of the forearm to the bones in the fingers. When the muscles in your forearm contract, the flexor tendons slide through the tunnel and pull on your finger bones, allowing you to make a fist (finger flexion).
The median nerve runs directly under the transverse carpal ligament. This nerve is responsible for the feeling in the thumb, index, middle, and the thumb side of the ring finger. It also controls the muscles in the thumb that allow you to pinch your thumb and fingers together.
Now that you know the anatomy, hopefully it will be easy for you to understand what causes the symptoms of carpal tunnel syndrome. People who have occupations or hobbies that require either repetitive or forced finger flexion (requiring use of the flexor tendons) are at risk for developing carpal tunnel.
Manual laborers, particularly those who encounter heavy vibration when operating machinery like a chain saw or jackhammer, can lead to irritation of the median nerve. Keyboard operators may be at some increased risk as well – typing 60 words per minute will move their flexor tendons in and out of the tunnel 18,000 times per hour!
The constant back and forth movement of the tendons through the tunnel can lead to swelling that puts pressure on the median nerve and causes it to become inflamed. The space in the tunnel becomes even more cramped when the wrist is bent down (flexed) or back (extended), causing even more pressure on the nerve. This inflammation of the nerve leads to the numbness and pain associated with carpal tunnel syndrome. The nerve fibers that form the median nerve exit the spinal cord in the neck and run down the arm to the wrist which explains why the pain can be found at any point along the path of these fibers.
Diagnosis of carpal tunnel is usually fairly straightforward. The history is often all that is needed. There are some simple physical exam tests that can also be done by a doctor. The tests increase the pressure in the tunnel or involve putting pressure directly on the nerve. Some cases are more difficult to diagnose and may require specialized electrical nerve testing to confirm involvement of the median nerve.
Once the diagnosis is made, the treatment is usually straightforward depending on the severity of the condition. Mild cases usually respond to activity modification by reducing repetitive motion of the fingers, intensity of gripping, or vibration. Splints that keep the wrist in a neutral position (not flexed or extended) can be helpful, particularly when worn at night. Anti-inflammatory medications may help as well. The goals of these treatments are to decrease the pressure in the tunnel and reduce inflammation, allowing the nerve to heal. People who don’t respond to activity modification and splinting may need to consider more invasive treatments such as injecting a steroid into the tunnel. Very severe cases can cause damage to the nerve, resulting in weakness of the muscles in the thumb. Patients that have pain that is unresponsive to these treatments or who have muscle weakness may need to undergo surgery to relieve the pressure by cutting the transverse carpal ligament. This is a fairly simple surgery that is usually quite successful if patients follow their post-operative instructions and don’t return to activity too soon.