Cornell University Ergonomics Web
CARPAL TUNNEL SYNDROME AND COMPUTER USE - IS THERE A LINK?
According to media reports of a recent research studies by researchers in
Denmark and those at the Mayo clinic in Scottsdale, Arizona, there is no association between
computer use and carpal tunnel syndrome (CTS) . This report apparently
contradicts widely held assumptions about the causes of computer-related
injuries, so what's the truth?
What is Carpal Tunnel Syndrome?
CTS is caused by compression of the median nerve as this passes through the
carpal tunnel, a narrow channel in the wrist between the carpal bones of the
wrist (tunnel roof) and the transverse carpal ligament (tunnel floor).
Sustained compression of the median nerve disrupts the axonal transport of
fluids and this causes damage to the nerve fibers, a process termed neuropathy.
The median nerve is a mixed nerve with both sensory and motor fibers. The
sensory fibers are those first affected, and intermittent paresthesia
(numbness, tingling) of the thumb and first two fingers often signifies the
early stages of CTS.
The Danish Study 
A questionnaire follow-up survey of 5,658 Danish workers was conducted one
year after a baseline survey had been completed by 6943 workers. The survey
collected self-report data on carpal tunnel syndrome symptoms. The prevalence
of self-reported symptoms at the baseline survey was 10.9%. The incidence of
new or worsened CTS symptoms at the 1-year survey was 5.5%. The prevalence of
median nerve symptoms at 1-year was 1.2%. At the baseline, there was no
association of psychosocial factors (high work demands, high job pressure, low
job control, low social support) or physical factors and possible CTS. At the
1-year follow-up, the average computer use for men was 8 hours per week and for
women was 9.3 hours per week and there was no significant association between
keyboard use and possible CTS. At the 1-year follow-up, the average mouse use
for men was 12.5 hours per week and for women was 14.7 hours per week and there
was a significant association between mouse use >20 hours per week and
possible CTS. The authors concluded that computer use is unrelated to carpal
Limitations with the Danish Study
The fact that the Danish workers only used their keyboard for an average of
8-9 hours per week is a serious limitation. This can hardly be considered
hardly intensive keyboard use, especially by US standards where workers
may be keying intensively for >30 hours per week. A
The Danish workers did make more intensive use of a mouse for an
average of 12-15 hours per week, and that the authors noted a significant
association between intensive mouse use and possible CTS, with an odds ratio of
3 for possible CTS for workers with >20 hours per week of mouse use.
Other recent Danish work has also found that mouse use increases
musculoskeletal injury risks. Both Danish studies found that there was no
association of psychosocial factors with injury risks. Contrary to Andersen et
al.'s conclusions, both Danish studies present results suggesting that computer
use is related to musculoskeletal injuries, such as possible CTS.
It may be unwise to generalize from computer workers in Denmark to those the
USA. In Denmark, by law the work week is shorter and ergonomic working
conditions are more regulated than in the USA. Providing a high quality working
environment is a legal requirement in Denmark and worker awareness of
ergonomics and the use of ergonomically designed furniture is widespread.
Ergonomists have always maintained that computer use need not increase
musculoskeletal risks if the workstation is ergonomically designed, and
Andersen et al.'s study may partly be confirming this. Unfortunately, unlike
Denmark, many US companies still fail to grasp the benefits of ergonomics, and
ergonomically designed workstations remain the exception rather than the rule.
The Mayo Clinic Study 
A questionnaire survey of workers using computers at the Mayo clinic in
Scottsdale, Arizona, was conducted. Complete data were received for a sample of
257 respondents (81.8% return rate). Some 95% of respondents were women. Of
these, 181 employees (70.4%) reported no symptoms of CTS, but 70 employees
(29.6%) did report hand paresthesia. From subsequent interview, 27 employees
(10.5%) were classified as having CTS. Of these employees, 9 people (3.5%) met
a clinical definition of CTS and showed changes in nerve conduction velocity.
Steven et al. conclude that this prevalence of CTS is comparable to that for
CTS among the general population, and therefore computer use cannot be
associated with the development of this syndrome.
Limitations with the Mayo Clinic Study
Before finally concluding that there is no association between CTS and
computer use it is worth considering the following issues:
- The conclusion of the Mayo study assumes that the 3.5% prevalence of CTS
that they reported (9/257) is that of the general population. The
researchers cite two studies on CTS prevalence in support of their
conclusion. One is a Dutch study  from the early 1990s, the other is a
more recent Swedish study . The Dutch study did not assess computer use. Given the changes in computer use patterns
throughout the 1990s, it is probably wisest to compare results with the
Swedish study. In this research, a survey of 2466 Swedes (46% men), aged 25
to74 years was conducted, and 14.4% of respondents reported hand paresthesia.
Clinical examination confirmed CTS in 94 symptomatic subjects (3.8%). At
first sight, the results from this and the Mayo study seem comparable (3.8%
vs 3.5%). However, in the Swedish study, 3.8% is the overall prevalence and
there are statistically significant effects of a number of variables,
including gender, age and occupational requirements. In the Swedish study,
the actually prevalence for CTS among office workers was 1.7%, which is half
of that reported by the Mayo clinic for a comparable population.
- The Swedish study shows that CTS prevalence rates peak between 45-65 years
of age. The mean age of workers in the Mayo study was 41 years, which
suggests that this population had not yet reached peak prevalence. It is
uncertain how many of the 25% of those who were hurting but who didn't meet
the strict clinical criteria for CTS, may develop this syndrome in the
- It is debatable whether the population of Sweden and the Netherlands are
representative of the U.S. population. A recent U.S. study by Nordstrom et
al.  found that newly diagnosed probable or definite carpal tunnel
syndrome (N = 309) occurred at a rate of 3.46 cases per 1,000 person-years,
or 0.35%. Another study  reported an industry-wide CTS incidence rate of
1.74 claims/1,000 FTEs. This puts the Mayo data at potentially 10 times the
normal population rate, although it is important not to place too much
emphasis on comparing prevalence and incidence numbers. Another larger U.S.
study of 127 million workers, found a self-reported CTS prevalence of
1.47% (95% CI: 1.30; 1.65), and 0.53% (95% CI: 0.42; 0.65) for medically
diagnosed CTS . Occupational risk factor most strongly associated with
medically called CTS were:
- exposure to repetitive bending/twisting of the hands/wrists at work
(OR = 5.2)
- race (OR = 4.2; whites higher than nonwhites)
- gender (OR = 2.2; females higher than males)
- use of vibrating hand tools (OR = 1.8)
- age (OR = 1.03; risk increasing per year).
- CTS is characterized as a progressive and chronic disorder. The Mayo study
provides a snapshot of current CTS injury prevalence. It is not clear how
this value will change with time, especially given that 1 in 3 workers was
experiencing some of the early signs of injury.
- No details are given of the occupational history of employees. Workers who
develop CTS either tend to be assigned to less computer intensive work in
organizations or they opt out of this type of work. The snapshot of the Mayo
workers gives no information on the extent to which this might be a
self-selected "healthy sample".
- The Swedish study used for comparison did not gather any data on computer
use, but the authors did conclude that occupational factors affected CTS
prevalence, especially "working with excessively flexed or extended
wrist". The Mayo study gives no information on the occupational risk
factors, such as extreme wrist postures, for those workers who did and did
not have CTS.
- Carpal tunnel syndrome specifically describes median nerve compression and
neuropathy within the carpal tunnel of the wrist. Similar symptoms may occur
if nerve compression occurs at other points along the median nerve (e.g.
elbow, shoulder, neck). There are also muscle syndromes that can mimic
carpal tunnel pain and compression at the neck accounted for 75% of CTS-like
- The Mayo study did not compare the prevalence rates for CTS among computer
users and non-computer users, and that is what needs to be done before any
definitive conclusion can be made. Also, the study doesn't say whether those
computer workers with and without CTS had received any ergonomics training
or whether any ergonomics interventions had been made. No data are presented
on the workers' postures or on non-work activities that could have
confounded the results. Given that there seems to have been widespread
complaints of musculoskeletal discomfort (at least 30% of workers), it is
doubtful that any good ergonomics program had been implemented.
- The Mayo study sample is relatively small and the extent to which this
might be representative of general office workers is unclear.
- The workers self-reported the hours of computer use. Such self-reports may
not be reliable. No measure of work intensity (e.g. number of keystrokes,
amount of mouse movements) was taken and this could differentiate those who
had the worst symptoms from others. Interestingly, the association of
mouse use and CTS was almost statistically significant (frequent mouse use:
CTS cases = 48.1%; non-CTS = 27.9%).
- The use of nerve conduction velocity as the primary diagnostic measure is
questionable. The Swedish study showed that there can be changes in median
nerve latency among people who otherwise appear asymptomatic. Consequently,
the Swedish prevalence data are based on a broader clinical definition. Any
change in the clinical criteria obviously changes the prevalence values, and
the use of only NCS probably underestimates the actual prevalence..
- The Mayo study news release says "those who had symptoms of numbness
or tingling but did not have carpal tunnel had mild symptoms that occurred
briefly. Some may have had problems with another nerve in the arm, the ulnar
nerve. Carpal tunnel affects the median nerve." The fact that there are
other problems confirms what we know, that inappropriate computer work may
relate to a variety of musculoskeletal problems.
- Syndromes such as CTS can take a long period of time to develop (several
years). The fact is that at the time of the study 30% of the sample were
experiencing intermittent symptoms, some 10 times the number with full-blown
carpal tunnel syndrome. Who's to say how many of those will develop CTS in
the coming years?
- Ergonomists have long maintained that to focus solely of carpal tunnel
syndrome is misleading, and that incorrect computer-use is associated with a
variety of musculoskeletal concerns. Steven's work seems to confirm this
when he says "Of the 257 people studied, 30 percent said they had
experienced pins and needles sensations or numbness in their hands."
When we assess workplaces we always assess discomfort and try to minimize
this, rather than trying to focus solely on an injury such as carpal tunnel
- Perhaps the most important statement from the news release from the Mayo
Clinic is the last line that says "Stevens said the results shouldn't
be interpreted to mean that the repetitive motions involved in using a
computer can never lead to problems for people." From personal
experience I know they do, and also from experience I know they can be
reversed and managed by proper ergonomic intervention.
What does it all mean?
Does computer use cause CTS? Ergonomists have never claimed that computer
use is the sole cause of CTS. Ergonomics research shows that computer users
often adopt poor wrist postures, and working in deviated postures is thought to
increase the risks of injury. Ergonomists have always maintained that computers
can be used safely providing the user works in a neutral posture. No assessment
of user posture was made in the Mayo study.
What the Mayo study has shown is the prevalence of CTS, characterized by median
nerve latency, among women working at the Scottsdale facility of the Mayo
clinic. In that respect the study is fine. However, the authors then proceed to
compare their results to prevalence data for a Dutch and a Swedish study, and
because the overall percentages look similar they assert that computer use has
not played any role in the Mayo workplace. That assertion is flawed for the
reasons described above. Thee media have reported this study as
"proving" that there is no association between computer use and
carpal tunnel syndrome, and that assumption too is flawed for the reasons
The Mayo study doesn't provide any definitive answer on the
association between computer use and CTS, and the truthful answer is that we
still don't know precisely what this is. What we do know is that computer-use
often is associated with a variety of musculoskeletal complaints, and these
adversely affect performance at work. We also know that musculoskeletal
complaints can be successfully prevented by working at a computer in a neutral
What the Danish study shows is that intensive mouse use is related to
possible CTS, and other variables, such as psychosocial factors, are unrelated.
For information on how to arrange a computer workstation for neutral posture
working see the adult workstation guide and the HealthyComputing.com
- Andersen, J.H., Thomsen, J.F., Overgaaard, E., Lassen, C.F., Brandt, L.P.A.,
Vilstrup, I., Kryger, A.I. and Mikkelsen, S. (2003) Computer use and carpal
tunnel syndrome: A 1-year follow-up study, JAMA, 289(22): 2963-2969.
- Jensen, C., Finsen, L., Søgaard, K., and Christensen, H. (2002)
Musculoskeletal symptoms and duration of computer and mouse use, Int. J.
Industrial Ergonomics, 30(4-5) , 265-275.
- Stevens, J.C., Witt, J.C., Smith, B.E. and A.L. Weaver (2001) The
frequency of carpal tunnel syndrome in computer users at a medical facility,
Neurology, 56, 1568-1570.
- De Krom M.C., Knipschild, P.G., Kester, A.D., Thijs, C.T., Boskkooi, P.F.
and F. Spaans (1992) Carpal tunnel syndrome: prevalence in the general
population. J. Clin. Epidemiol. 45, 373-375.
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Rosén, I. (1999) JAMA, 282 (2) 153-158.
- Nordstrom, D. L., F. DeStefano, et al. (1998). Incidence of diagnosed
carpal tunnel syndrome in a general population. Epidemiology 9 (3): 342-5.
- Franklin, G. M., J. Haug, et al. (1991). "Occupational carpal tunnel
syndrome in Washington State, 1984-1988." Am J Public Health 81(6):
- Tanaka, S., D. K. Wild, et al. (1995). "Prevalence and
work-relatedness of self-reported carpal tunnel syndrome among U.S. workers:
analysis of the Occupational Health Supplement data of 1988 National Health
Interview Survey [see comments]." Am J Ind Med 27(4): 451-70.