FELICIA WILLIS

It's called the no. I occupational hazard.

Do you suffer from tingling, burning, or numbness in your fingers? Have you experienced aching in your hand, difficulty gripping, or problems making a fist? Did these symptoms first appear at night? Are these traits most prevalent in the thumb, index, and middle fingers?

Figure 1. Tunnels and nerves. The median nerve (yellow) can become pinched as it runs through the carpal tunnel, the space between the wrist bones and the transverse carpal ligament (white). This leads to numbness or pain and the loss of function in parts of the hand and fingers associated with carpal tunnel syndrome.

If you’ve experienced any of these symptoms, you’ve probably fallen victim to carpal tunnel syndrome (CTS) and have joined the >31,000 cases that are diagnosed each year in the United States. The carpal tunnel is a small passage that runs between the wrist bones and the stiff transverse carpal ligament (see Figure 1). Nine tendons and the median nerve, which supplies both sensation and strength to the hands, run through the tunnel.

According to the U.S. Department of Labor, CTS has become one of the most significant work-related medical problems of the past decade. Computer operators, assembly line workers, meat packers, construction workers, and cashiers alike are casualties of the repetitive strain injuries triggering this disorder and earning it the label, “the number one occupational hazard”.

CTS has a variety of causes and is typically the result of a combination of factors. CTS occurs when the median nerve is compressed as it runs through the tunnel. Anything that narrows the available space for the median nerve—swelling or inflammation of the tendons, fluid accumulation (as in pregnancy), genetic predisposition, injuries and trauma (such as a blow to the wrist or lower arm), health, lifestyle, repetitive motion, bone changes from arthritis—can result in CTS or aggravate a preexisting condition.

Recent studies show that CTS affects more women than men by almost 3 to 1. CTS does not favor one hand over another and can occur in one or both hands. Anyone can be susceptible to this disorder, but those who may be at an increased risk for CTS include

• pregnant women,
• birth control pill users,
• menopausal women,
• sufferers of premenstrual syndrome,
• rheumatoid arthritis sufferers,
• people with myxedema (a thickening of body tissues due to low levels of thyroid hormone),
• people with acromegaly (abnormal body growth due to excess growth hormone),
• people who experience job stress,
• alcoholics, and
• obese individuals.

Scientists have concluded that people who consistently use computer mice and trackballs also have an increased risk of CTS, because of repetitive hand motion. People who type or use a computer keyboard can decrease their risk of CTS by making sure that they keep their wrist joints straight rather than bent. This position can be maintained by using any of several aids including cushioned, adjustable keyboard trays and middle-hinged keyboards.

If a lot of time is spent at a desk, the workstation should be checked to make sure it is ergonomically sound to reduce stress on the wrists and promote good posture. The World Health Organization and the U.S. Department of Health and Human Services have conducted numerous studies showing that effective ergonomic design can substantially reduce the risk of repetitive motion injuries.

An Exercise in Prevention: 1. With extended arms, hold your hands up at a right angle as though pushing against a wall, and hold for five seconds. 2. Straighten your hands and relax your fingers. 3. Make tight fists and bend both wrists down, holding for five seconds. 4. Straighten both hands and relax the fingers as before, holding for five seconds. 5. Repeat these steps 10 times and then drop your arms at your side, shaking them every few seconds.

The first line of treatment is to adjust the way the person performs a repetitive motion. Changing the frequency with which motions are performed and changing the length of rest periods can do this. Other ways to prevent or limit CTS include maintaining straight wrists while sleeping and when using tools, avoiding repeated wrist flexing and extension, minimizing repetitive motions, resting when possible, and performing conditioning and stretching exercises (shown at right). Rest allows the swollen and inflamed synovial membranes to shrink, thereby relieving the pressure on the nerve. For extremely mild cases, using a brace or splint, which is usually worn at night, may help. Splints keep the hand in a position that prevents the wearer from causing even more damage from bending or twisting at the wrist and also reduces pressure. Splints are often used in conjunction with drug therapies.

Drugs that reduce swelling, specifically nonsteroidal anti-inflammatory drugs (NSAIDs), are the most common treatment for CTS. By reducing swelling, pressure is decreased and, if the median nerve is not too badly damaged, its function can be restored. NSAIDs such as aspirin, naproxen, and ibuprofen are the best option in treating early stages of CTS because they can decrease inflammation and relieve pain and discomfort. Unfortunately, in many cases, the tissues are permanently enlarged, and no amount of drugs can reduce their size.

In cases of severe pain, steroids such as cortisone are injected directly into the carpal tunnel and can bring significant and immediate relief. These compounds spread and shrink the swollen synovial membranes surrounding the tendons, providing temporary relief from the pressure on the median nerve. The dosage of cortisone typically has no harmful side effects. The effectiveness of these nonsurgical treatments is often dependent on early diagnosis and treatment.

Over the past 20 years, studies and case reports have suggested that a deficiency in vitamin B₆ might contribute to CTS. So far, no controlled studies have sufficiently tested the B₆ hypothesis in a large, randomly selected group of people. Occupational and Environmental Medicine has published several studies on CTS; they have mostly determined which types of people are affected and what brings on repetitive motion disorders.

In very advanced cases, a procedure called a carpal tunnel release operation is performed (for a QuickTime movie of the procedure, visit www.scoi.com/ctr.mov). It involves cutting the transverse carpal ligament and allowing it to heal back together. This gives more room for the soft tissues and therefore reduces pressure. This surgery is expensive and usually requires many weeks of recovery. It is also far from being a guaranteed cure. There is, however, another approach. Although the transverse carpal ligament doesn’t automatically stretch to accommodate swelling, it can be stretched externally. This technique can be used as a preventive method or treatment for CTS.

If surgery is the only option, the ligament across the tunnel is slit open to allow more room for the tendons inside. The first surgeries for CTS used an incision through the wrist and palm. Many doctors now use an arthroscope, which allows a much smaller incision but may not always be as effective. Laser surgery is the newest variation on this theme, and it also uses a small incision. Whether laser CTS surgery is more effective than other approaches has yet to be determined.

New research from the Center for Carpal-Tunnel Studies in Paradise Valley, AZ, indicates that a combination of massaging techniques and exercises performed at home may relieve CTS without surgery. The efficacy of this approach has yet to be determined.

Further reading

The journal Occupational and Environmental Medicine has published several articles on CTS. Those listed below best exemplify the current understanding of the disorder.

1. Gorsche, R. G., et al. Prevalence and incidence of carpal tunnel syndrome in a meat packing plant. Occup. Environ. Med. 1999, 56, 417–422.
2. Leclerc, A., et al. Carpal tunnel syndrome and work organisation in repetitive work: A cross sectional study in France. Study Group on Repetitive Work. Occup. Environ. Med. 1998, 55, 180–187.
3. Nordstrom, D. L.; Vierkant, R. A.; DeStefano, F.; Layde, P. M. Risk factors for carpal tunnel syndrome in a general population. Occup. Environ. Med. 1997, 54, 734–740.
4. Rossignol, M.; Stock, S.; Patry, L.; Armstrong, B. Carpal tunnel syndrome: What is attributable to work? The Montreal study. Occup. Environ. Med. 1997, 54, 519–523.

Felicia Willis is an editorial assistant for Modern Drug Discovery. Send your comments or questions regarding this article to mdd@acs.org or the Editorial Office by fax at 202-776-8166 or by post at 1155 16th Street, NW; Washington, DC 20036.

 © 2001 American Chemical Society.  

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