I see a number of people each month who suffer from carpal tunnel syndrome. Carpal tunnel is a very common condition, often related to repetitive injury at home or in the workplace. It is one of a number of repetitive strain injuries or "RSI's."
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 diagram). There are eight carpal bones that make up the wrist. When you hold your wrist with your palm facing up, these bones form a U-shaped cavity. The top of the cavity is enclosed by a piece of connective tissue called the transverse carpal ligament. These structures together form the carpal tunnel.
The tunnel is a very cramped space and some very important structures are packed into it. There are 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 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 part of the ring finger. It also controls the muscles in the thumb that allow you to pinch your thumb and index finger 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 and people who operate keyboards are the most common sufferers of carpal tunnel. Heavy vibration when operating machinery like a chain saw or jackhammer can also cause problems. Keyboard operators 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. This inflammation of the nerve leads to the numbness and pain associated with carpal tunnel. The space in the tunnel becomes even more cramped when the wrist is bent down or back, causing even more pressure on the nerve.
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 are also recommended to keep the wrist in a neutral position (not flexed or extended). Anti-inflammatory medications can 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 that don't respond to activity modification and splinting may need to consider more invasive treatment such as an injection of cortisone 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 have the pressure relieved by having surgery to cut 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.