Computer Keyboard Design Reduces Hand Pain

Researchers have found that a new computer keyboard design can decrease hand paresthesia numbness, tingling, or 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 of carpal tunnel syndrome," said study director and COEH faculty member David Rempel. "The study showed that a significant reduction in symptoms is possible with a simple intervention modifying the springs underneath each key that change the force and feel of the key switches."

Study findings showed that at six weeks there was no significant difference in pain levels between keyboard groups. However, after 12 weeks participants who used the keyboard with modified keys experienced a significantly greater reduction in hand pain compared with participants using the more traditional keyboard.Rempel and research colleagues selected 20 participants full-time employees of LLNL in Livermore, California who reported to the occupational medicine clinic for hand or wrist symptoms within six months of the start of the study. Patients were eligible to participate in the study if they (1) met the criteria for possible carpal tunnel syndrome; (2) used a computer keyboard for at least two hours per 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 hand or wrist.

Researchers paired participants according to both the amount of time spent at a computer per week and which hand experienced pain. Of the pair, one was assigned to keyboard A, with the new keyswitch design, while the other was assigned to keyboard B, with conventional keys. Both keyboards were similar in external appearance. The difference, said Rempel, was the force displacement characteristics of the springs underneath the redesigned keys, resulting in a difference in the amount of force needed to depress the computer keys. Participants used the assigned keyboards for 12 weeks.

Prior to the intervention, participants provided their medical history and underwent physical examinations, and nerve conduction tests, which reveal how well the nerve is functioning by measuring 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/or tingling occurred in the fingers. This test is also called the Phalen test time and is considered an indication of the severity of carpal tunnel syndrome, said Rempel. Researchers found an improvement in the Phalen test but no change in the nerve conduction test before and after the use of both keyboards.Given these findings Rempel and research colleagues recommend the following:

Results of the study were reported in the February 1999 issue of the Journal of Occupational and Environmental Medicine.Co-authors of the study are Pat Titteranonda, graduate of the ergonomics program and now a post doctoral fellow at LLNL, Stephen Burastero, occupational medicine physician at LLNL, Mark Hudes, senior biostatistician at UC Berkeley, Yeun So, associate professor of neurology at Stanford University and clinic director of neurology at UCSF Stanford Health Care at Stanford.