Effects of computer mouse design and task on carpal tunnel pressure.
ABSTRACT Computer mouse use has become an integral part of office work in the past decade. Intensive mouse use has been associated with increased risk of upper extremity musculoskeletal disorders, including carpal tunnel syndrome. Sustained, elevated fluid pressure in the carpal tunnel may play a role in the pathophysiology of carpal tunnel syndrome. Carpal tunnel pressure was measured in 14 healthy individuals while they performed tasks using three different computer mice. Participants performed a multidirectional dragging ('drag and drop') task starting with the hand resting (static posture) on the mouse. With one mouse, an additional pointing ('point-and-click') task was performed. All mice were associated with similar wrist extension postures (p = 0.41) and carpal tunnel pressures (p = 0.48). Pressures were significantly greater during dragging and pointing tasks than when resting the hand (static posture) on the mouse (p = 0.003). The mean pressures during the dragging tasks were 28.8-33.1 mmHg, approximately 12 mmHg greater than the static postures. Pressures during the dragging task were higher than the pointing task (33.1 versus 28.0 mmHg), although the difference was borderline non-significant (p = 0.06). In many participants the carpal tunnel pressures measured during mouse use were greater than pressures known to alter nerve function and structure, indicating that jobs with long periods of intensive mouse use may be at an increased risk of median mononeuropathy. A recommendation is made to minimize wrist extension, minimize prolonged dragging tasks and frequently perform other tasks with the mousing hand.
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ABSTRACT: Controlled external compression was applied to the medium nerve of 16 volunteer subjects. Tissue fluid pressure in the carpal canal was monitored with a wick catheter and pressures of 30, 60 and 90 mm Hg were induced for periods varying from 30 to 90 minutes.l Sensory and motor conduction and two-point discrimination were continuously monitored. Tissue compression at 30 mm Hg caused mild neurophysiological changes and symptoms of hand paresthesias. Compression at both 60 and 90 mm Hg induced a rapid, complete sensory conduction block which consistently preceded a motor block by 10 to 30 minutes. Frequently, two-point discrimination remained normal until the last stages of preserved sensory fiber conduction. In three cases, a modification of the model utilizing an arm tourniquet, demonstrated that ischemia rather than mechanical deformation was the primary cause of the functional deterioration. It was concluded that there is a critical pressure level between 30 and 60 mm Hg where nerve fiber viability is acutely jeopardized.The Journal Of Hand Surgery 06/1982; 7(3):252-9. · 1.57 Impact Factor
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ABSTRACT: OBJECTIVE: The study examined the change in intracarpal canal pressure (ICCP) in relationship to finger, hand, wrist and forearm position. DESIGN: The study was an in vivo measurement of ICCP in seven subjects undergoing a standardized set of manoeuvres that systematically varied finger, hand, wrist, and forearm position. BACKGROUND: It has been known that the ICCP increased with extremes of wrist flexion and extension but the change in pressure in response to radial and ulnar deviation as well as hand and forearm position has not been reported. METHODS: The ICCP was measured using a slit catheter technique; each variation of position was repeated three times with continuous monitoring of ICCP, wrist angulation, and metacarpal-phalangeal joint angulation. RESULTS: The study demonstrated that ICCPs were lowest when the wrist is in a neutral position, the hand relaxed with fingers flexed and the forearm in a semi-pronated position. Wrist extension and flexion resulted in the greatest increase in ICCP followed by forearm pronation and supination. Radial and ulnar deviation also increased the pressure but to a lesser extent. CONCLUSIONS: The findings of this study support the concept that the wrist and forearm should be maintained in a neutral position during vocational and avocational activities in an effort to minimize pressure within the carpal tunnel and thereby reduce the risk of developing carpal-tunnel syndrome. RELEVANCE: It is desirable to know how the ICCP changes in response to change in hand, wrist, and forearm position so that work activities are designed to minimize the pressure within the carpal canal and thus maintain the viability of the median nerve within the carpal canal.Clinical biomechanics (Bristol, Avon) 02/1997; 12(1):44-51. · 1.76 Impact Factor
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ABSTRACT: The purpose of this study was to explore the relationship between carpal tunnel pressure and fingertip force during a simple pressing task. Carpal tunnel pressure was measured in 15 healthy volunteers by means of a saline-filled catheter inserted percutaneously into the carpal tunnel of the nondominant hand. The subjects pressed on a load cell with the tip of the index finger and with 0, 6, 9, and 12 N of force. The task was repeated in 10 wrist postures: neutral; 10 and 20 degrees of ulnar deviation; 10 degrees of radial deviation; and 15, 30, and 45 degrees of both flexion and extension. Fingertip loading significantly increased carpal tunnel pressure for all wrist angles (p = 0.0001). Post hoc analyses identified significant increase (p < 0.05) in carpal tunnel pressure between unloaded (0 N) and all loaded conditions, as well as between the 6 and 12 N load conditions. This study demonstrates that the process whereby fingertip loading elevates carpal tunnel pressure is independent of wrist posture and that relatively small fingertip loads have a large effect on carpal tunnel pressure. It also reveals the response characteristics of carpal tunnel pressure to fingertip loading, which is one step in understanding the relationship between sustained grip and pinch activities and the aggravation or development of median neuropathy at the wrist.Journal of Orthopaedic Research 05/1997; 15(3):422-6. · 2.88 Impact Factor
EŒects of computer mouse design and task on carpal tunnel
PETER J. KEIR², JOEL M. BACH and DAVID REMPEL*
Ergonomics Program, Department of Medicine, University of California,
San Francisco, CA, USA
Keywords: Ergonomics; Computer mouse; Input device; Carpal tunnel syndrome;
Carpal tunnel pressure.
Computer mouse use has become an integral part of o?ce work in the past
decade. Intensive mouse use has been associated with increased risk of upper
extremity musculoskeletal disorders, including carpal tunnel syndrome. Sus-
tained, elevated ¯uid pressure in the carpal tunnel may play a role in the
pathophysiologyof carpal tunnel syndrome. Carpal tunnel pressure was
measured in 14 healthy individuals while they performed tasks using three
diŒerent computer mice. Participants performed a multidirectional dragging
(`drag and drop’) task starting with the hand resting (static posture) on the mouse.
With one mouse, an additional pointing (`point-and-click’) task was performed.
All mice were associated with similar wrist extension postures (p = 0.41) and
carpal tunnel pressures (p = 0.48). Pressures were signi®cantly greater during
dragging and pointing tasks than when resting the hand (static posture) on the
mouse (p = 0.003). The mean pressures during the dragging tasks were 28.8 ±
33.1 mmHg, ~12 mmHg greater than the static postures. Pressures during the
dragging task were higher than the pointing task (33.1 versus 28.0 mmHg),
although the diŒerence was borderline non-signi®cant (p = 0.06). In many
participants the carpal tunnel pressures measured during mouse use were greater
than pressures known to alter nerve function and structure, indicating that jobs
with long periods of intensive mouse use may be at an increased risk of median
mononeuropathy. A recommendation is made to minimize wrist extension,
minimize prolonged dragging tasks and frequently perform other tasks with the
The computer mouse has become an important input device that has created
new problems in today’s workplace (Fogleman and Brogmus 1995). There have
been anecdotal and research reports that intensive computer mouse users are at
musculoskeletal disorders (Franco et al. 1992, Franzblau et al. 1993, Karlqvist
et al. 1994). However, unlike the keyboard, the number of studies that have
Fogleman andBrogmus (1995) reviewed
workers’ compensation claims and
*Author for correspondence at: UCSF Ergonomics Program, 1301 South 46th Street,
Building 112, Richmond, CA 94804, USA. E-mail: rempel@ itsa.ucsf.edu
²Present address: Kinesiology and Health Science, York University, Toronto, Ontario,
Canada M3J 1P3.
ERGONOMICS, 1999, VOL. 42, NO. 10, 1350 ± 1360
Ergonomics ISSN 0014-0139 print/ISSN 1366-5847 online Ó 1999 Taylor & Francis Ltd
claims, the problem was growing and deserved research attention.
People are now required to use the computer mouse as an input device for
large proportions of their workday. Johnson et al. (1993) analysed 10 people
performing word processing, spreadsheet/database, or graphics/drawing applica-
tions and found that mouse use constituted 31, 42 and 65%
respectively. As a general rule, it appears that computer users spend one- to
two-thirds of their computer work using the mouse. Karlqvist et al. (1994)
examined the postures associated with mouse use versus keyboard-only use.
Although postural diŒerences were noted, large variances and a brief testing
period were deemed responsible for the lack of statistical signi®cance. They
using the mouse than using the keyboard.
Sustained elevated carpal tunnel pressure has been proposed as a causative
factor in carpal tunnel syndrome (Rempel 1995). Carpal tunnel pressure is
individuals when the wrist is deviated from neutral (Gelberman et al. 1981,
Okutsu et al. 1989, Rojviroj et al. 1990, Werner et al. 1997). Nerve function and
structuremay be compromisedif the
> 30 mmHg (Hargens et al. 1979, Lundborg et al. 1983, Powell and Myers
1986, Dahlin et al. 1987).
The aim of this study was to determine whether diŒerences in the design of a
computer mouse in¯uence wrist postures and carpal tunnel pressure. Further-
more, does mousing activity, in and of itself, increase carpal tunnel pressure?
With each mouse, the postures and pressures were compared between holding the
mouse (static posture) and using mouse during a `drag-and-drop’ task. With one
mouse, an additional comparison was made between the `drag-and-drop’ task and
a `point-and-click’ task.
thatalthoughmouse-related claimswereasmall proportionofall
of each task
greater percentage of
syndrome as well asinhealthy
Fourteen participants with no signs or symptoms of carpal tunnel syndrome
participated in this study. There were nine men and ®ve women with a mean (range)
age of 31 (22 ± 45) years. All participants used the right hand.
2.2. Participant medical examination
Each participant was interviewed and examined by a physician for the signs
(thumb opposition, interossei, grip) and thenar atrophy. Sensation to touch in
the hand and ®ngers was tested, as were Phalen’s and Tinel’s signs. Each
participant hadan electrodiagnostic study
muscle recording, measuring antidromic sensory conduction between the wrist
and index ®nger and recording the orthodromic short-segment between the
palm and the wrist. The ®ndings of the history, physical examinations and
nerve conduction studies were normal for all participants. Participants were
recruited from postings of notices at the university. This study was approved
by theCommittee onHumanResearch,
ofthe mediannerveby thenar
Universityof California atSan
Mouse design and carpal tunnel pressure
2.3. Materials and task
Each participant used three computer mice (®gure 1): `mouse A’, a prototype of the
Contour Mouse (Multipoint Technology, Lowell, MA, USA); `mouse B’, the Apple
II ADB Mouse (Apple Computer, Inc., Cupertino, CA, USA); and `mouse C’, the
Microsoft Serial Mouse (Microsoft Corp., Redmond, WA, USA). A dragging task
(`drag-and-drop’) was performed with each mouse and an additional pointing task
(`point-and-click’) was performed with mouse C. Following the template in ®gure 2,
the dragging task started at the top circle (labelled `1’), and followed the progression
as indicated by the arrows. After clicking and holding the mouse button depressed
on circle 1, the next target (circle 2) in sequence became dark and the current target
was dragged to the darkened target where it was `dropped’ by releasing the mouse
button. The cycle then began again with the darkening of circle 3. The pointing task
(only mouse C) followed the same sequence except that the participant simply
clicked the mouse button over each successive target. Prior to the initiation of each
task, the participant assumed a static (functional) posture with the hand holding the
mouse, then on cue began the dragging or pointing task.
The participant was seated and the workstation was adjusted so that the mouse
was approximately at elbow height and its use did not require shoulder ¯exion. The
top of the monitor was just below eye level. Participants could make ®ne adjustments
for comfort if desired. Prior to starting the study, participants practised until they
were familiar with all mice and tasks.
Figure 1. The three mice evaluated. Left to right: mouse A, B, C.
P. J. Keir et al.
2.4. Experimental set-up
Carpal tunnel pressure was measured by means of a saline-®lled, multiperforated 20-
gauge (0.8 mm) catheter (Burron Medical, Inc., Bethlehem, PA, USA) inserted
percutaneously into the carpal tunnel of the right hand and connected to a pressure
transducer (Rempel et al. 1994). The pressure transducer was maintained at the same
elevation as the carpal tunnel. To minimize the possibility of occlusion, a slight
positive ¯ow of physiologic saline at 0.5 ml h
continuous ¯ush device (model 42002-02; Sorenson Intra¯ow II).
Ð 1was maintained using a low-¯ow
depressed on circle 1 (top), the next target in sequence (circle 2) turns dark. The captured
target is dragged (indicated by arrows) to the now darkened target and `dropped’ by
releasing the mouse button. The cycle then begins again with the darkening of circle 3,
and continues until all targets are eliminated. Pointing: this task (mouse C only) follows
the same sequence except that the participant simply clicks the mouse button after
pointing to each successive darkened target.
Mousing task template. Dragging: after clicking and holding the mouse button
Mouse design and carpal tunnel pressure
A biaxial electrogoniometer (Penny and Giles, Gwent, UK) was a?xed to the
dorsum of the participant’s hand and wrist. The goniometer provided radioulnar and
¯exion ± extension angles. Calibration of the device included deviation to known
angles as well as de®ning a zero or neutral wrist position for each participant (Greene
and Heckman 1994). In addition, a resting posture was determined for each
participant. This posture was de®ned as the repeatable hand posture in which the
lowest carpal tunnel pressure was observed; usually at a neutral wrist posture with
the forearm pronated to 458 (Weiss et al. 1995). The pressure transducer and
goniometer calibration protocols have been described previously (Weiss et al. 1995).
Outputs from the pressure transducer and the goniometer were digitally sampled
at 40 Hz and stored on a computer.
2.5. Statistical analyses
Mean wrist postures and carpal tunnel pressure were calculated for each participant-
mouse type-task over the duration of each task. The data were analysed using a
repeated measures ANOVA while speci®c post hoc analyses used the Tukey ± Kramer
HSD test (a = 0.05). For the ®rst analysis the main eŒects were mouse type and task
(static versus dragging); for the second analysis only data from mouse C were used
and the main eŒects tested were dragging versus pointing and static versus active.
Mean resting (lowest) carpal tunnel pressure prior to placing the hand on the
mouse was 5.361.0 mmHg (mean6SEM). The mean pressures rose to 18.763.8,
16.864.4 and 18.463.4 mmHg for mice A to C respectively, after the hand was
placed on the mouse (i.e. static posture). The mean pressures rose further during
the dragging tasks to 28.866.0, 31.166.1 and 33.166.7 mmHg for mice A to C
respectively (table 1); the diŒerences between mice were not signi®cant (p> 0.48).
An example of the continuous pressure and wrist posture during a dragging task
is presented for one participant in ®gure 3. The pressure and wrist angles
¯uctuated slightly as the task was performed. The mean pressures for each
participant and task are presented in the plot in ®gure 4. It can be seen that there
was a marked diŒerence in pressure response across the study participants. The
mean pressure obtained during the dragging task (table 1) was ~12 mmHg
greater than that measured while assuming a static position on the mouse, a
signi®cant diŒerence (p = 0.003).
Acomparison between the pointing and
demonstrated that the task of dragging increased carpal tunnel pressure more
than during a pointing task (33.1 versus 28.0 mmHg), which was borderline non-
signi®cant (p = 0.06). Again, the pressure diŒerence between active pointing with
themouseand staticpostureon the
(p = 0.005).
No signi®cant diŒerences in wrist ¯exion angle were found between any of the
mice tested; between the static postures or while using the mouse. All of the mice
tested promoted an extended wrist angle between 25 and 308 during the tasks and 23
to 288 in the static postures (table 1). While there were no statistical diŒerences in
wrist ¯exion ± extension angle between the mice or with respect to active or static
posture, there was a signi®cant diŒerence in the radioulnar angle between the mice
(p = 0.0004). Mouse A led to a slightly more neutral posture in the active position
and a more radial posture in the static position (table 1) than did the other two mice.
dragging tasks with mouse C
P. J. Keir et al.
Mean wrist posture (6SE) and carpal tunnel pressure for each mouse during static positioning and during the mousing tasks (n= 14).
Carpal tunnel pressure (mmHg)
1Positive values indicate wrist extension.
2Positive values are wrist ulnar deviation; negative values are radial deviation.
Mouse design and carpal tunnel pressure
None of the radial and ulnar deviations exceeded 5.28 from neutral. There were no
signi®cant diŒerences between genders in wrist postures or carpal tunnel pressure.
The time required (mean6SD) to complete the dragging task was 71.2621.5,
76.0625.6 and 66.0623.9 s for mouse A to C respectively. The pointing task
required less time to complete (56.266.7 s).
Under the conditions used in this study, we have found that the three computer
mouse designs tested were associated with similar carpal tunnel pressures and wrist
postures. We have also determined that carpal tunnel pressure is greater during
computer mouse use than when the hand is statically positioned over the mouse.
There is a trend (p = 0.06) for a repeated dragging task to increase carpal tunnel
pressure to a greater extent than a similar pointing task.
Our results indicate that although the shape of the three mice tested altered
radioulnar deviation, there was no diŒerential eŒect on carpal tunnel pressure.
Pressure responds very little to small changes in radioulnar deviation angle near the
neutral wrist posture (Rempel et al. 1997a). It is unlikely that these conclusions
would change even if the number of participants was increased.
Carpal tunnel pressures measured while performing mousing tasks were found to
attain a level of concern (®gure 4). Active use of the mouse elevated the pressure in
Figure 3.Continuous data from one participant performing the dragging task with mouse A.
Carpal tunnel pressure ¯uctuates around a relatively stable mean as the participant
performs clicking and dragging. Task start and completion times are marked with vertical
lines. Values are degrees or mmHg; negative values are extension or radial deviation/
convention (diŒers from table 1).
P. J. Keir et al.
the carpal tunnel to ~30 mmHg. Prolonged pressure of this magnitude has been
associated with altered nerve function and structure in human and animal nerve
studies (Hargens et al. 1979, Lundborg et al. 1983, Powell and Myers 1986, Dahlin et
al. 1987) as well as eliciting symptoms of carpal tunnel syndrome when induced in
the carpal tunnel (Lundborg et al. 1982). These changes in tissue physiology may be
the ®rst step in a cascade of events that lead to carpal tunnel syndrome (Dahlin et al.
1987, Rempel 1995). This indicates that individuals who use a mouse for long
durations (e.g. CAD operators) may be at a higher risk for developing carpal tunnel
syndrome or aggravating existing symptoms. This is consistent with the ®nding of
increased risk of carpal tunnel syndrome among graphic artists who used mice
extensively (Franzblau et al. 1993). In a limited number of graphic artists, Franzblau
et al. found an increased rating of pain in the hand and forearm over that reported
by the non-graphic artist o?ce workers.
The diŒerences seen in pressure with active use of the mouse correspond to
our previous studies that found elevated carpal tunnel pressure with increased
®ngertip force (Rempel et al. 1997b, Keir et al. 1998). Magnitudes of ®ngertip
force applied to the button during mousing tasks are ~1.5 ± 2.0 N when averaged
over time while forces applied to the sides of the mouse may be as high as 4 N
(Johnson et al. 1994). The eŒects of these forces on carpal tunnel pressure have
not been tested previously. However, ®ngertip loads of 5 or 6 N lead to carpal
tunnel pressures of 15 ± 40 mmHg (depending on wrist and forearm posture),
which are signi®cantly greater than pressures without ®ngertip loading (Rempel et
al. 1997b, Keir et al. 1998).
The near signi®cant (p = 0.06) ®nding that the dragging task created higher
pressures than the pointing task deserves discussion. With a larger participant pool
Figure 4.Mean carpal tunnel pressure for each participant, mouse and task. Each
participant is represented by a diŒerent marker (n= 14).
Mouse design and carpal tunnel pressure
this diŒerence would likely have been statistically signi®cant. There are two factors
that diŒer between dragging and pointing with the mouse. First, the button is
depressed for a greater percentage of the task cycle during dragging. Second, pinch
forces on the side of the mouse are about three times greater during dragging tasks
than pointing tasks (Johnson et al. 1994). This means there is greater ®ngertip
loading of longer duration during a dragging task than during pointing. The increase
in pressure with dragging is consistent with a previous study that evaluated carpal
tunnel pressure during pinching (Keir et al. 1998).
Mousing, in general, promotes a fully pronated forearm. Forearm rotation has
been shown to aŒect carpal tunnel pressure (Rempel et al. 1998, Werner et al.
1997). However, from the data in both papers, it appears that there is relatively
little eŒect of pronation in the range tested. The data from Rempel et al. (1998)
indicate minimal eŒect of forearm posture, from neutral to full pronation, on
carpal tunnel pressure. Werner et al. (1997) used large gradations for wrist angle
extension,20 ± 608
diŒerences between `pronated’ and `semi-pronated’ forearm positions (8.3 versus
9.5 and 15.6 versus 12.8 mmHg). Although these data indicate that the eŒect on
carpal tunnel pressure is small, a forearm not fully pronated may lead to slightly
lower pressures when the wrist is extended to 20 ± 308, the posture observed
during mouse use in this study.
Two factors may account for the elevated carpal tunnel pressure during
computer mouse use: (1) wrist extension and (2) the ®ngertip force applied to
depress the button and to grip the sides of the mouse. A recent study in our
laboratory of 37 healthy individuals found that a wrist extension angle of >308
created a carpal tunnel pressure that was signi®cantly greater than that associated
with the neutral wrist position (Rempel et al. 1997a). From a design perspective,
some options are to promote training and workstation, software and tool designs
that reduce wrist extension, reduce the duration of elevated forces applied during
computer mouse use (e.g. minimize dragging tasks) and limit the duration of
continuous mouse use. We propose that, if used, computer mouse workstation
forearm supports be designed to reduce wrist extension angle and that employees
be educated about methods to reduce wrist extension, especially if mouse use is
intensive and of long duration.
There are several limitations to this study. First, the exposure period was brief
(< 90 s per task). However, preliminary data from participants performing keyboard
work for 20 min indicate that mean carpal tunnel pressure is stable for that duration.
Second, the workstation was not a conventional workstation. Third, the task is
arti®cial although it was designed to mimic typical pointing tasks. Fourth, the
sample size was relatively small; a larger sample size would have reduced the chance
of a type II error (failing to reject a false null hypothesis). Fifth, the carpal tunnel
pressure measured in this study represents the interstitial ¯uid pressure and does not
include the direct contact pressures that may also restrict the vascular supply to the
median nerve. Sixth, the study was limited to healthy individuals. The changes in
carpal tunnel pressure during wrist motion in patients with carpal tunnel syndrome
are similar in direction to, but larger than, pressures in healthy individuals (Weiss et
al. 1995). Generalization of these data to clinical or symptomatic individuals should
be reserved until further research with those populations has been conducted.
Although the mice tested were somewhat diŒerent, their designs were not extreme,
that is, they were all variations of the `classic’ mouse design.
extension) andalso foundminimal
P. J. Keir et al.
No important diŒerences in wrist posture or carpal tunnel pressure were observed
between the three computer mice tested. There was, however, a signi®cant increase in
carpal tunnel pressure when using the mouse as opposed to resting the hand on the
mouse (i.e. static posture). It is possible that using a mouse for long duration may
exposesome individualsto carpal tunnel pressure
pathophysiologic events that lead to carpal tunnel syndrome. We suggest that
eŒorts be made by employees, employers and manufacturers to reduce the wrist
extension associated with mouse use, reduce sustained button down activities (e.g.
dragging) and interrupt prolonged mouse usage with other tasks for the mousing
hand. Further studies investigating the incidence and prevalence of carpal tunnel
syndrome and other musculoskeletal disorders among intensive mouse users are
We thank Ron Tal for his technical assistance. The study was performed at the
University of California at Berkeley’s Richmond Field Station in the Environmental
Engineering & Health Sciences Laboratory.
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