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Carpal tunnel from mouse not keyboard { June 17 2003 }

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PC Use Not Key to Pain
Mouse a Bigger Player in Carpal Tunnel, Says Study

By Suz Redfearn
Special to The Washington Post
Tuesday, June 17, 2003; Page HE01

Frequent on-the-job use of a computer keyboard does not pose a major risk for carpal tunnel syndrome, according to the largest study of the topic to date. The findings were published June 11 in the Journal of the American Medical Association (JAMA).

While the conclusion flies in the face of popular belief -- many office workers who use computers are convinced their symptoms of finger numbness, tingling and pain are caused by their hours at the keyboard -- smaller studies have shown similar results to the JAMA research. But critics say the new study fails to account sufficiently for people who use computers more than 20 hours a week, those who may be at higher risk because of heavier mouse use or those with other computer-related injuries that are not strictly defined as carpal tunnel syndrome. The study also considered computer use only over a period of a year.

Carpal tunnel syndrome, marked by a severe compression of the median nerve in the wrist, is associated with one of the most common surgeries in the United States.

To conduct the study, Danish researchers followed more than 5,600 members of a trade union for a year, scrutinizing their use of a keyboard and mouse. At the beginning and end of the study, participants were asked about specific symptoms on a questionnaire. Complaints that met a prescribed frequency and severity threshold were confirmed by clinical exam. At baseline, only 4.8 percent of the participants reported a prevalent tingling and numbness of the wrist, and only about 1.4 percent had symptoms at night, when many people with carpal tunnel syndrome typically feel increased pain. One year later, 5.5 percent reported new or worsened symptoms, but only 1.2 percent had symptoms in the median nerve.

Experts expressed little surprise at the findings. "It's exactly what any study done with any vigor will find," said Robert Szabo, surgeon and professor of orthopedic surgery at the University of California, Davis, School of Medicine.

But what about all we were told in the 1980s and '90s about how too much time at the keyboard could harm us? Turns out none of that was backed up with science; it was all just common belief, says Szabo, who sat on a seminal National Academy of Sciences panel on musculoskeletal disorders and the workplace in 2001.

"Computers causing [carpal tunnel syndrome] was a myth. No science has ever shown that any medical disorders are caused by using a keyboard," he said. "This is finally coming out in the mainstream."

Force Is Key
The causes of carpal tunnel syndrome have been hotly debated for two decades -- since the condition first became widely discussed. Known causes include pregnancy, wrist trauma, diabetes and rheumatoid arthritis. If splints, drugs (mainly painkillers and corticosteroids) and exercises don't relieve persistent pain, a surgeon may sever the band of tissue around the wrist to reduce pressure on the median nerve. But recovery after surgery can take months, and some patients never regain full wrist strength.

Medical experts aren't sure how repetitive hand and finger movements on a keyboard or with a mouse affect nerve structure and function.

What scientists do know is that carpal tunnel syndrome is mostly caused by pressure. Explains Gary Franklin, medical director of Washington state's Department of Labor and Industries, those at highest risk for the ailment are people who work with their hands in jobs that require frequent repetition and force. Picture a worker in a meatpacking plant cutting into one slab of meat after another or a lumberyard worker lifting piles of planks from a sawmill, Franklin said. The next highest category of risk is seen among those who use only force regularly on the job. The category with the least risk attached to it is repetition only. That, says Franklin, encapsulates computer use.

"Just typing does not increase your risk," said Franklin. "The force you use on a computer is minimal."

The Danish research supports a smaller 2001 study. In that case, a Mayo Clinic neurologist studied secretaries, transcribers and other employees at the clinic who typed for much of their day. Of the 30 percent who reported tingling in their hands, only 10.5 percent were diagnosed with carpal tunnel syndrome.

According to the Bureau of Labor Statistics (BLS), three of every 10,000 workers were diagnosed with the condition in 2001, the most recent year for which such numbers are available. The BLS numbers show that fewer than 1 percent of all full-time computer and data processing workers were diagnosed with carpal tunnel syndrome that year, in contrast with 12 percent of meatpackers. Says Szabo, being female and a smoker and over 55 puts people at far greater risk than does computer use.

Mouse Matters
But while the Danish researchers may have exonerated the computer keyboard as a leading villain, the mouse remains suspect. According to the study, there was a small but significant association between use of a mouse device for more than 20 hours per week and a risk of carpal tunnel syndrome.

Franklin and others call this finding important because as more Internet functions demand mouse clicks, computer users are increasingly relying on their mouse more than their keyboard. People at particular risk, he said, are those who work in design or drafting or who use the Internet for several hours a day.

In the Danish study, mean mouse use was just under 15 hours per week for women and 121/2 hours for men. Mean keyboard use was more than nine hours per week for women and eight hours for men.

David M. Rempel, a professor of occupational medicine at the University of California, San Francisco, School of Medicine and also a member of the National Academy of Sciences panel, says this level of use was insufficient to draw conclusions about either keyboard or mouse use. Usage under 20 hours a week, says Rempel, is not representative of people who do data entry or design for a living.

"The conclusions you can draw there are pretty limited," said Rempel. "What about graphic artists and reporters, who might be exposed to their computers for 20, 30 or 40 hours a week?"

In addition, said Rempel, the study didn't address any of a range of other ailments he said can result from prolonged computer use. These, he said, include tendinitis of the wrist and elbow -- inflammatory conditions often accompanied by stiffness, soreness and pain -- as well as trapezius muscle strain, which causes soreness around the shoulder blade; the latter condition can often be remedied by changing positions to better support the forearm. Prolonged computer use, said Rempel, will cause approximately 10 to15 percent of workers to develop wrist tendinitis; 30 percent can expect trapezius muscle strain. "All eyes are on carpal tunnel syndrome, but we need to look at the whole gamut of problems that can come from repeated computer use," he said.

The fact that much of the damage is cumulative also raises the question of whether a year's study was long enough to draw conclusions. "It may be that five years of follow up would have resulted in more cases of carpal tunnel syndrome," said Franklin. "But because of the length of the study, that data wasn't there." Added Szabo, "Your risk of CTS increases with age (shown in every study ever done on this) whether you stay on the job or not."

Despite such criticism, Rempel called the Danish study strong and compelling, and predicted other studies would reach similar conclusions about keyboards.

In the meantime, said Szabo, don't expect advocacy groups and policymakers to stop contending that computers are crippling workers.

"It takes time for politics to follow science," he said.

Suz Redfearn last wrote for the Health section about the local medical community's response to SARS.

2003 The Washington Post Company

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