Carpal Tunnel Syndrome

I have seen many people who suffered from carpal tunnel syndrome. Carpal tunnel is very common, often 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 from sleep.

To understand carpal tunnel, 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 form the carpal tunnel.

The carpal tunnel is a cramped space with very important structures traversing it. There are nine flexor tendons and the median nerve. The tendons 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 and 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 touch your thumb to your fingers.

Knowing the anatomy makes it easier to understand what leads to the signs and symptoms of carpal tunnel syndrome. Occupations or hobbies requiring repetitive or forced finger flexion (using the flexor tendons) increase the risk for developing carpal tunnel.

Manual laborers, particularly those who encounter heavy vibration when operating machinery like a chain saw or jackhammer, frequently suffer 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 leads to swelling that puts pressure on the median nerve causing inflammation. The space in the tunnel becomes even more cramped when the wrist is bent toward the palm (flexed) or back (extended), causing additional pressure on the nerve. The nerve inflammation leads to the numbness and pain associated with carpal tunnel syndrome. The fibers that form the median nerve leave the spinal cord in the neck and course down the arm to the wrist. This is why the pain can be found at any point along the path of these fibers.

Diagnosing 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 medical provider. The tests increase the pressure in the tunnel or put 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 responsible for thumb movement. Patients with pain that is unresponsive to these treatments or who have muscle weakness may need to undergo surgery to relieve the pressure. This is done 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.

Dr. John Roberts is a retired member of the Franciscan Physician Network specializing in Family Medicine.