Feb. 16, 1999 A study led by UC San Francisco and UC Berkeley researchers has found that a new computer keyboard design can decrease hand paresthesia -- numbness, tingling, burning in the hand -- experienced by frequent computer users.
"This is the first randomized clinical study to demonstrate that keyboard design can reduce pain in computer users who have hand discomfort similar to symptoms in carpal tunnel syndrome," said David Rempel, MD, UCSF associate professor of medicine and director of the UC San Francisco and UC Berkeley Ergonomics Program. "The study showed that a significant reduction in symptoms is possible with a simple intervention -- using springs underneath each key that change the force or feel of the key switches."
Results of the study were reported in the February 1999 issue of the Journal of Occupational and Environmental Medicine.
Study findings showed that after 12 weeks, participants who used a keyboard with modified keys, experienced a significantly greater reduction in hand pain compared with participants using a keyboard which required more force on the keys. However, at six weeks, there was no significant differences in pain levels between keyboard groups.
Rempel and research colleagues conducted the 12-week long study to evaluate the effects of keyboard keyswitch design -- varying the springs underneath each key -- on patients with hand pain and physical examination findings consistent with carpal tunnel syndrome.
Researchers selected 20 participants, full time employees of Lawrence Livermore National Laboratory in Livermore, CA who reported to the occupation medicine clinic for hand or wrist symptoms, within six months of the start of the study.
Patients were eligible for participation if they 1) met the criteria for possible carpal tunnel syndrome 2) used a computer keyboard for at least two hours a day or ten hours per week 3) had been employed in their current job for at least three months and 4) had no prior surgery of the hands or wrist.
Researchers matched or paired participants according to self-reported average computer usage hours per week and to the hand that experienced pain. One patient of the pair was assigned to keyboard A, the new keyboard, while the other was assigned to keyboard B, the control. Both keyboards were similar in external appearance. The difference, said Rempel, was the force displacement characteristics of springs underneath the keys, resulting in a different feel or force of the computer keys. Participants used the assigned keyboards for 12 weeks.
Participants received a medical history, physical examination, and nerve conduction tests prior to the intervention. The nerve conduction test, a traditional tool to measure how well the nerve is functioning, measured how fast an electrical signal travels through the nerve. Additional health measures collected at six weeks and 12 weeks included self-reported symptoms, hand function tests, and physical examinations. With the hand function test, participants were asked to flex their wrist to maximum, maintain the position for 60 seconds, and report when, if at all, symptoms of numbness and tingling occurred in the fingers. The duration of time from when the wrist is bent to the onset of the symptoms is called the Phalen test time and is considered an indication of the severity of carpal tunnel syndrome, said Rempel.
"For participants using the new keyboard, improvement in hand pain was delayed, occurring after 12 weeks of use." said Rempel. "In addition, findings show improvement in Phalen test time suggesting a positive effect of the new keyboard."
Researchers also found no difference in the nerve conduction test before and after the use of both keyboards.
Given these findings Rempel and research colleagues recommend the following:
* Health care providers who care for computer users with hand discomfort may recommend a three-month trial of a keyboard with the different key switches.
* Computer users with hand pain, should reduce time on the keyboard and take adequate breaks from the computer.
* Computer users should modify work station layout so the keyboard is not too high and so they do not have to stretch to reach for the computer.
* Keyboards with new designs do not replace medical interventions. Computer users and health care professionals should not ignore traditional treatments for hand pain and carpal tunnel syndrome.
The UC San Francisco and UC Berkeley Ergonomics program conducts research on injury and the mechanisms of tendons and nerves in hands and arms related to repetitive use of hands at work. In addition, the program investigates the role of hand tool design in preventing injuries. The Center for Disease Control (CDC) and private industry funds the research.
Co-authors of the study are Pat Tittranonda, PhD, post doctoral fellow, Lawrence Livermore National Laboratory; Stephen Burastero, MD, occupational medicine physician, Lawrence Livermore National Laboratory; Mark Hudes, PhD, senior biostatistician, University of California Berkeley; Yeun So, MD, PhD, associate professor of neurology at Stanford University and clinic director of neurology at UCSF Stanford Health Care at Stanford.
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