Repetitive Hand Use Not the Culprit in Carpal Tunnel

By Amanda Gardner
HealthDay Reporter
Friday, February 16, 2007; 12:00 AM

FRIDAY, Feb. 16 (HealthDay News) -- Go ahead, type the night away. New research has found that genetics, rather than repetitive hand use, is responsible for carpal tunnel syndrome.

"This study has shown that there really is a genetic predisposition to carpal tunnel," said Dr. Roy G. Kulick, chief of hand surgery in the department of orthopedics at Montefiore Medical Center in New York City. Kulick was not involved with the study.

Which is not to say that genetics provide the whole answer.

"Age, genetics, obesity, diabetes, thyroid, various types of hormonal conditions, even pregnancy are predisposing factors," said Dr. George Pianka, chief of hand surgery at Lenox Hill Hospital in New York City. "Then, there are external factors that will bring up symptoms, so I think it's fair to say that a person may have a genetic or multi-factorial predisposition, and something may aggravate the symptoms or allow the symptoms to manifest."

"Probably the most accepted stance is that there are, within the population, susceptible groups that will develop carpal tunnel," added Dr. Richard Schultz, an assistant professor of surgery at Texas A&M Health Science Center and chief of staff at Scott & White University Medical Campus at Round Rock. "How much of a role environment has on those susceptible groups is probably where the debate is. Most people would feel comfortable saying that you have to be almost genetically preselected to be in one of those susceptible groups."

The new findings, expected to be presented Friday at the American Academy of Orthopaedic Surgeons annual meeting in San Diego, turns popular wisdom on its head.

"This [repetitive hand use, such as typing] has gotten into newspapers and into one's psyche. There is a gut reaction: 'I use my hands a lot, and I have carpal tunnel, therefore, one must be related to the other,'" Kulick said. "But there has never really been strong scientific, controlled studies showing that there is an association between repetitive stress and carpal tunnel."

Added Pianka: "This is not something new [among the scientific establishment]. Twenty years or so ago, it became a kind of media frenzy, and people in the [medical establishment] did not counter those inaccurate statements. Now, we have to go back and do scientific studies and refute something that wasn't done scientifically in the first place. It ran away with itself."

Carpal tunnel syndrome occurs when the median nerve in the wrist is compressed for long periods of time. This compression can cause permanent nerve damage if left untreated. According to the U.S. National Institutes of Health, carpal tunnel syndrome is five times more common in women than in men and most often occurs in people between the ages of 30 and 60.

Patients with carpal tunnel syndrome experience numbness in the hands and eventually develop weakness and atrophy of some of the small hand muscles that control the thumb.

For the new study, researchers compared evidence for biological and occupational causes of carpal tunnel syndrome using the Bradford Hill criteria, an accepted quantitative measure.

The average scores for biological causes such as genetics, age and race were twice those of occupational factors such as repetitive hand use. Also, the average strength of a cause-and-effect association was three times as strong for biological factors as for occupational factors.

The findings fit with prior knowledge. "One would expect a higher percentage of people who use their hands continuously and laboriously to get carpal tunnel, and that's never been the case," Kulick said. "Construction workers don't get it any more frequently. The smaller community of court reporters who don't stop all day for hours and hours, they don't really develop it any more than anyone else."

According to the study authors, the findings may affect disability, workers' compensation and personal-injury claims.

But, the conclusions aren't likely to have any bearing on treatment, although they may change discussions regarding prevention.

"We do not totally understand why it occurs, so it's hard to prevent," Kulick said. "Treatment would be the same."

More information

For more on carpal tunnel, visit the American Academy of Orthopaedic Surgeons.

SOURCES: Roy G. Kulick, M.D., chief, hand surgery, department of orthopedics, Montefiore Medical Center, and associate professor, orthopedic surgery, Albert Einstein College of Medicine, New York City; Richard Schultz, M.D., assistant professor, surgery, Texas A&M Health Science Center and chief of staff, Scott & White University Medical Campus at Round Rock; George Pianka, M.D., chief, hand surgery, Lenox Hill Hospital, New York City; Feb. 16, 2007, presentation, American Academy of Orthopaedic Surgeons annual meeting, San Diego

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