As I type these words, signals travel from my brain to the nerves in my spinal cord, down nerve roots that supply the arms and then into smaller and smaller nerves that tell the small muscles in the wrist and fingers to flex. Muscles contract, others relax and tendons tug at the ends of my fingers, which tap on the keys — not too hard, not too soft, just enough to depress the key without injuring myself or the keyboard. It is a complex process that occurs in less than a second, and for many people, this type of activity is repeated thousands of times each day.
Perhaps the most amazing thing is that for the vast majority of movements like these, nothing goes wrong. But sometimes things do go wrong. A host of problems thought to be caused by computer use have been reported. Carpal tunnel syndrome is among the most common of these.
What Is Carpal Tunnel Syndrome?
Carpal tunnel syndrome is a compressive neuropathy in the wrist; that is, a nerve within the wrist is compressed as it travels through a narrow stretch of bone, cartilage and tendons called the carpal tunnel. The nerve involved is the median nerve, which provides sensation to the thumb, index finger, middle finger and half the fourth finger and supplies muscles that allow the thumb to forcefully pinch.
Contrary to popular belief, pain is not the most prominent feature of carpal tunnel syndrome; instead, numbness, tingling and/or weakness within the hand, wrist or forearm are the most typical features. Because everyone has a median nerve traveling through a rather narrow carpal tunnel, the reason why some people develop this problem and others do not is not always clear. Risk factors include inflammation in the wrist (as in rheumatoid arthritis or related conditions), pregnancy, certain repetitive motions or injuries, thyroid disease and diabetes. A significant number of people have carpal tunnel syndrome for no clear reason.
The Role of Computer Use
Movements that bend the wrist, especially when prolonged or repetitive, increase pressure within the carpal tunnel and may provoke symptoms of nerve compression. It is easy to understand how repetitive trauma to the wrist, such as jackhammer use, might provoke nerve injury. In fact, most studies of carpal tunnel syndrome and the workplace have examined people in meat-packing plants and other industrial occupations.
Computer users, whose wrist position when typing or using the mouse also could place them at risk, have been the subjects of only a handful of studies, none of them definitive. Some of these studies actually showed no association between computer use and carpal tunnel syndrome.
It now appears that the assumption that computer use causes carpal tunnel syndrome may be wrong — a myth perpetuated by intuition and evidence that is circumstantial. An important study (appearing in the June 2001 issue of the journal Neurology) carefully analyzed symptoms and the results of physical examination and nerve testing in 257 employees of the Mayo Clinic who regularly used a computer (an average of six hours per day) as part of their work. The incidence of carpal tunnel syndrome in these workers (3.5%) was similar to that in the general population.
Other important findings were reported. Temporary symptoms of numbness or tingling were experienced frequently, but these either resolved promptly on their own or were caused by a separate problem. Although many people working at computers have symptoms such as pain (which may be related to tendinitis or another condition related to overuse), the Neurology study did not support the notion that computer use provokes carpal tunnel syndrome.
A more recent study that appeared in the June 2003 Journal of the American Medical Association also found no association between symptoms of carpal tunnel syndrome and computer use. Finally, at least one study — appearing in the November 2007 edition of Arthritis and Rheumatism — found a reduced risk of carpal tunnel syndrome among intensive keyboard users.
Still, the evidence is not strong enough either way to settle the issue. Despite a number of studies arguing against a connection, studies linking carpal tunnel syndrome with keyboard use continue to appear. For example, a study published in 2012 found a correlation between the number of keyboard keystrokes and the risk of carpal tunnel syndrome among governmental data entry and processing employees in Greece.
The Bottom Line
Larger studies examining which work-related activities contribute to which conditions are needed. Although the latest data dispute the connection between carpal tunnel syndrome and frequent use of a computer keyboard or mouse, there are still simple interventions that may prevent other problems, including worsening of pre-existing carpal tunnel syndrome:
Take nothing for granted. The presumed link between computer use and carpal tunnel syndrome is a good example of how a well-accepted "fact" turns out to be suspect. Only well-controlled analyses can help distinguish a medically valid assumption from myth.
Robert H. Shmerling, M.D., is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.