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Am Fam Physician. 2004;69(3):643-647

Carpal tunnel syndrome is reported to occur with similar frequency among computer users and the general population, with a prevalence of 0.7 to 9.2 percent in women and 0.4 to 2.1 percent in men. Andersen and colleagues conducted a study to determine whether computer use played a role in promoting carpal tunnel syndrome.

The Neck and Upper Extremity Disorders Among Technical Assistants (NU-DATA) study is a one-year follow-up trial examining the relationship between computer use and neck and upper extremity disorders. Participants completed a baseline questionnaire related to three outcome measures: finger tingling and numbness in the right hand; median nerve tingling, numbness, or pain in the right hand; and median nerve symptoms at night. At one year, participants were questioned about right-hand numbness and tingling and median nerve symptoms, particularly if no symptoms had been present at baseline.

Mean mouse use was 14.7 hours per week in women and 12.5 hours per week in men, and keyboard use was 9.3 hours per week and 8.0 hours per week, respectively. Examiners also extracted information about mouse, keyboard, and forearm position, as well as chair position and satisfaction with work environment.

At one-year follow-up, there were 5,658 respondents and 1,285 nonrespondents. The overall self-reported baseline prevalence of right-hand tingling and numbness was 10.9 percent, with 4.8 percent experiencing median nerve tingling and numbness, and 1.4 percent experiencing symptoms at night. At one-year follow-up, the incidence of new or worsened carpal tunnel syndrome symptoms was 5.5 percent, with 1.2 percent having median nerve symptoms. Most participants remained at the same symptom level, and those who improved (9.1 percent) during the year exceeded those whose symptoms worsened (7.7 percent). Because the proportion of participants missing at follow-up was greatest among those with no symptoms and lowest among those with more frequent symptoms, it is unlikely that baseline symptoms selected out symptomatic patients.

At baseline, tingling and numbness were associated with mouse use, but inclusion of symptoms at night showed that this association was only significant for mouse use exceeding 30 hours per week. None of the posture variables were associated with any of the outcomes, nor was keyboard use. Dissatisfaction with work environment carried a slightly greater risk for the studied outcomes. Psychosocial risk factors were not associated. Women had a slightly increased risk. A non-significant increased association with the three outcomes was found in patients with other medical conditions, smoking, and older age.

At follow-up, possible carpal tunnel syndrome was associated with mouse use, with a somewhat irregular exposure pattern when used fewer than 20 hours per week. Mouse use more than 20 hours per week was observed to be a risk factor for becoming an incident case of self-reported tingling and numbness. Too few participants developed median nerve symptoms to be included in multivariate analysis. When changing mouse and keyboard use from baseline to follow-up was included, odds ratios were 0.98 in those who used a mouse more and 0.77 in those who used a mouse less. Mean difference in mouse use in those who developed or experienced worsening symptoms was 0.3 (standard deviation, 6.9) hours per week, and in those who experienced resolved or improved symptoms, the mean difference was 1.5 (standard deviation, 7.9) hours per week.

This study found that the incidence of possible new or aggravated carpal tunnel syndrome after one year was 5.5 percent, compared with a baseline prevalence of 1.4 to 4.8 percent. When median nerve symptoms were included, the incidence dropped to 1.2 percent. According to the most rigorous definition of carpal tunnel syndrome, including night symptoms, elevated risk of carpal tunnel syndrome occurred only with mouse use of more than 30 hours per week; mouse use of more than 20 hours per week was associated with numbness and tingling.

This study did not support the notion that keyboard use is a risk factor for carpal tunnel syndrome, although the authors recognize that frequent and intensive keyboard use may have a small impact on risk. Use of the mouse was associated with symptoms in the cross-sectional comparisons and the follow-up analyses. However, the authors did not find a consistent linear pattern of increased risk with increased mouse use and conclude that carpal tunnel syndrome has multiple causes, some of which may be the stresses and strains of everyday life.

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