Heavy computer use may not cause CTS after all

Study seems to indicate no direct linkage

For years, professionals involved in employee health have commonly held the belief that heavy computer use and the attendant repetitive motion are primary contributors to carpal tunnel syndrome (CTS). Now, however, a new study by the Mayo Clinic indicates there may be no direct linkage at all between CTS and extensive use of computers.

The study, published in the June 2001 issue of Neurology,1 was led by J. Clarke Stevens, MD, a neurologist with Mayo in Rochester, MN. Stevens formerly served as chair of the department of neurology at the Mayo Clinic in Scottsdale, AZ. Conducted in Scottsdale in 1995, the research included 257 Mayo employees who were heavy computer users.

Although 29.6% of the employees reported hand paresthesias, just 24 (10.5%) met clinical criteria CTS, and in only seven (3.5%) was the syndrome confirmed by nerve conduction studies. (See table, below.) Bottom line: The frequency of CTS in these computer users was similar to that in the general population. "This suggests that using a computer in the setting studied does not enhance the risk of CTS,"1 the researchers concluded.

Carpal Tunnel Syndrome (CTS) Criteria
Symptom Possible CTS
(n=17)
Clinical/NCS*
Definite CTS
  (n=9)

Awakened by paresthesia 9 (52.9%) 7 (77.8%)
Hand goes to sleep driving 8 (47.1%) 5 (55.6%)
Hand goes to sleep reading 7 (41.2%) 6 (66.7%)
Relief by shaking hand 11 (64.7%) 7 (77.8%)

* NCS = Nerve Condition Studies
Source: Stevens JC, Witt JC, Smith BE, Weaver AL. The frequency of carpal tunnel syndrome in computer users at a medical facility. Neurology 2001; 56:1,568-1,570.

Even researchers surprised

Even the researchers admit to being surprised by the study’s findings. "They were unexpected," admits Stevens. "Like everybody else, we thought we’d find a much higher incidence of CTS."

However, as noted in the study, there is not a significant body of literature on the subject. Why, then, is the linkage between computer use and CTS so widely assumed? "I really don’t know how that got to be," Stevens concedes. "There’s really nothing in the literature. People say it is due to the repetitive motion of typing. But if that’s true, CTS should have been epidemic when people were using manual typewriters, which are a lot tougher on the fingers. I wonder if it isn’t because people get a lot of other neck and upper extremity discomfort with computer use. We did ask our subjects about symptoms of the neck, arm, shoulder, and wrist, and discomfort was very high, even in those who didn’t have CTS. So there is that association, and maybe that’s how the perception of a linkage grew."

The researchers did look at the use of typewriters, but found no differences. "You also would expect to see greater discomfort among those workers who used computers longer, or more during the day, or who were older," says Stevens, "But they were identical in nearly all aspects — age, sex, and years of computer use."

The participants also were asked about symptom onset, and many mentioned waking up at night, or feeling symptoms when they drove a car, read the paper, or put their hands up. "They almost never tell me they get symptoms when they use a computer," says Stevens.

If computers are not a major source of CTS, then what causes the condition? "In just under half of them, there is no obvious cause," Stevens observes. "The biggest risk factors seem to be being female, in your 40s and 50s, and being a homemaker. For the remainder, there are a whole host of other causes — wrist fractures, trauma, diabetes, rheumatoid arthritis, and so forth."

Despite the apparent vindication of the computer, CTS is a very real condition and a threat to employee health and productivity. What steps can occupational health professionals take to help prevent the onset of CTS? "People have suggested the reason our employees are not getting a higher percentage of CTS is that their workstations are set up so well," says Stevens. "Maybe, we could do a study of people with bad workstations, or with poor positioning, and see if more of them got CTS."

One thing remains clear to Stevens: providing workers with ergonomically correct workstations is still very important. "Ergonomically incorrect workstations cause a lot of other discomforts," he notes. "It would also be interesting to know if having ergonomically correct workstations also help prevent CTS. It would be a great study to do if you could figure it out."

(For more information, contact: J. Clarke Stevens, MD, Neurologist, Mayo Clinic, 200 First St. S.W., Rochester, MN 55905.)

Reference

1. Stevens JC, Witt JC, Smith BE, Weaver AL. The frequency of carpal tunnel syndrome in computer users at a medical facility. Neurology 2001; 56:1,568-1,570.