The current study is the first clinical study of a keyboard with patients diagnosed with carpal tunnel syndrome. Previous research has compared the angular motion of the fingers in a comparison of QWERTY, Dvorak and Finger Relief keyboards (Robertson et al., 1995). However, in these studies the subjects had no diagnosis of carpal tunnel syndrome.
The typing test used typical English word combinations of letters which could be easily repeated for any layout. On the QWERTY keyboard, pressing the D and E flexes the middle finger. TheOrdinals letters (A D E H I L N O R S T) on QWERTY has 6 flexions, 1 each for the left middle; right middle, right ring, right index, 2 each left index fingers. TheOrdinals on Finger Relief keyboard have no flexions or extensions of the fingers The keystrokes were noted. The goal was to type to pain, change in feeling, numbness or tingling. The beginning and ending time was recorded manually with reference to a wristwatch or clock. Each of the four typing sessions ranged from 20 minutes (very little typing occurred) to more than an hour (extensive typing occurred without a report of symptoms). Pretyping measurement activities took about 10 minutes, including completing the analogue scaled self reporting test and water displacement test. Following this pretyping data collection, the subject was instructed to type until a change in pain was noticed. Post-typing measurement activities, including water displacement, a check for swelling, and self-report measures also took about 10 minutes.
The subject was then scheduled to return to the clinic no sooner than until an overnight had passed, or after any swelling has gone down. The protocol was repeated on a similar keyboard with only the letters rearranged. On the Finger Relief keyboard, pressing the D and E requires minimal flexion, as pressing the middle and index finger on the home row communicates the letters.
The study population was those who had been diagnosed with carpal tunnel syndrome. The FDA asked that the reference group consist of 20 individuals (no restrictions for the number of men and women). There were no minimum or maximum requirements of age, subjects were only required to have a history of carpal tunnel syndrome or similar problems when performing typing activities prior to study enrollment. Each subject confirmed a history of carpal tunnel syndrome, presumably causing difficulties in performing typing activities. However typing problems were not required for participation.
A total of 64 subjects responded to the study advertisements. Thirty-three of these subjects did not enter the study. Many were missing either the NCVS or a diagnosis of carpal tunnel syndrome from a doctor (14). Several did not respond to attempts to schedule study sessions (8). A few moved away from the area prior to study participation (4) or were too ill to participate (2). The remainder had insufficient interest to commit to participate in four testing sessions (3); were looking for treatment options, rather than a CTS study (1); or were advised by an attorney to decline participation in a CTS study, pending litigation that the subject was pursuing (1).
Thirty-one subjects completed the all steps before beginning the typing exercises, which included a medical history, informed consent, CTS diagnosis, and NCVS confirming the CTS diagnosis. Eleven withdrew or left the testing incomplete. Ten of the eleven dropouts were employed at office work, the other was employed as a registered nurse. Five withdrew prior to initiating study sessions. Six withdrew after beginning a study session but before completing the remaining sessions and did not respond to efforts to schedule the remaining tests. Four dropouts started with the QWERTY layout. Two started with Finger Relief. Four dropouts completed only one study session (three started with QWERTY, one began with Finger Relief). Two dropouts completed two study sessions (one began with QWERTY, one started with Finger Relief). Twenty subjects completed all 4 study sessions and are included in the analyses described in later sections of this application.
Swelling is a hallmark of CTS, because the median nerve must be compressed. Prior to this study, it was unknown whether swelling could be externally measurable in the least severe cases. Although the literature suggests that there is some swelling in all stages (1, 2 or 3) of CTS cases, the literature did not designate swelling by stage. Classic inflammation is measured by fever (rise in temperature), color (redness), swelling and pain. Only swelling and pain are externally measurable, without invasive procedures. The pre typing hand and wrist volume were the base line from which swelling was measured. Assuming typing causes measurable swelling, before the subsequent typing sessions, a sufficient time had to have passed for the swelling to return to base line. Thus, base line was defined as a return of external parameters (pain and swelling) to that which was measured before the first typing test session.
Swelling was measured by comparing the increase in hand volume before and after the activity as measured by the water displacement method. Water displacement was measured to determine if an increased amount of water from the hand and wrist measurement was displaced after typing on QWERTY keyboard as compared with typing on the TheOrdinals (the Finger Relief keyboard) keyboard. It was hypothesized that there would be a significant relationship between the increased amount of water and the use of the QWERTY keyboard.
The data were analyzed using a personal computer and statistical software. Calculations between the differences of means of swelling and pain, between the QWERTY and TheOrdinals (the Finger Relief keyboard) keyboards were completed. Regression techniques were used to estimate the differential impact of typing with each keyboard on swelling and pain. Means differences and regression techniques were also used to examine the effect of keyboard type on duration of typing.
