Surprising even the researchers themselves, a new study from Mayo Clinic found that heavy computer use, even up to seven hours per day, did not increase a person’s risk of carpal tunnel syndrome (CTS). The results of the research, to be published in the June 12 issue of Neurology, indicate that only 10.5 percent of the study participants, all of whom used computers extensively, met clinical criteria for CTS. This incidence is similar to that found in the general population in past studies, according to the authors of Mayo Clinic’s manuscript. “We had expected to find a much higher incidence of carpal tunnel syndrome in the heavy computer users in our study because it is a commonly held belief that computer use causes carpal tunnel syndrome,” says J. Clarke Stevens, M.D., a neurologist at Mayo Clinic in Rochester, Minn., and lead author of the study.

Mayo Clinic Scottsdale News Monday, June 11, 2001 Mayo Clinic Scottsdale Study Debunks Possible Link Between Heavy Computer Use and Carpal Tunnel Syndrome SCOTTSDALE, ARIZ. — Surprising even the researchers themselves, a new study from Mayo Clinic found that heavy computer use, even up to seven hours per day, did not increase a person’s risk of carpal tunnel syndrome (CTS). The results of the research, to be published in the June 12 issue of Neurology, indicate that only 10.5 percent of the study participants, all of whom used computers extensively, met clinical criteria for CTS. This incidence is similar to that found in the general population in past studies, according to the authors of Mayo Clinic’s manuscript. “We had expected to find a much higher incidence of carpal tunnel syndrome in the heavy computer users in our study because it is a commonly held belief that computer use causes carpal tunnel syndrome,” says J. Clarke Stevens, M.D., a neurologist at Mayo Clinic in Rochester, Minn., and lead author of the study. “The other finding was that among our cases of carpal tunnel syndrome, two-thirds of them had very mild carpal tunnel syndrome. Our study results were unexpected,” said Dr. Stevens. Dr. Stevens formerly served as chair of the Department of Neurology at Mayo Clinic in Scottsdale, Ariz. This is the first major study to consider the association between the syndrome and computer usage. “The findings are contrary to popular thought, but nobody has studied the problem carefully,” says Dr.Stevens. “There has been very little formal study of carpal tunnel syndrome in computer users, and there is not much to find in the literature on this topic. We studied computer users because though there is a commonly held notion that using a computer causes CTS, there really have been few studies published that looked at this in a scientific way.” Dr. Stevens offers a message of relief for those who may have wondered about their risks of the so-called “office plague” due to long hours spent in front of a computer. “I’d like computer users to know that prolonged use of a computer does not seem to lead to carpal tunnel, at least not in our employees who used computers up to seven hours per day,” says Dr. Stevens. Carpal tunnel syndrome is a common condition in the population, however, which means that some computer users will develop carpal tunnel syndrome. Our study suggests, however, that the risk of developing the syndrome is not increased by working at a computer.” Dr. Stevens indicates that though computer use may not be as highly associated with CTS as thought, it is associated with numerous other medical issues. “Carpal tunnel syndrome in computer users has been thought of as a repetitive motion disorder, and it has been assumed that computer use might cause carpal tunnel syndrome as part of such a disorder. People who use the computer do get a lot of other aches and pains in the neck, shoulder, arm and wrist, but most of them do not get carpal tunnel syndrome from using a computer.” As CTS is not the only ergonomics issue related to computer usage, a correct office setup still has great merit, according to Dr. Stevens “The question arises as to whether ergonomically correct work stations are important,” he says. “I think they continue to be very important, because there are a variety of aches and discomfort that can result from using a computer. A majority of the computer users in our study, including those without carpal tunnel syndrome, had experienced neck and upper extremity pain during the two years prior to the study. “What we are saying is that at least in our employees studied, computer use did not seem to increase the risk of getting carpal tunnel syndrome.” There are a variety of factors that do contribute to CTS, according to the study authors. “The major risk factors for developing carpal tunnel syndrome are being female and middle-aged,” says Dr. Stevens. “There are many other causes of carpal tunnel syndrome, such as wrist trauma, diabetes, rheumatoid arthritis and pregnancy.” Repetitive motions in industries outside the office also have been linked to CTS, Dr. Stevens says. “There is certainly a whole variety of other jobs that are much more labor-intensive that we think might cause carpal tunnel syndrome, such as working in a meat packing plant or using a jackhammer,” says Dr. Stevens. “There have been a number of studies of factory workers and people in packing plants that suggest that type of repetitive motion does seem to be associated with carpal tunnel syndrome.” Though the Mayo Clinic study authors consider their study to be an important first step in studying CTS and computer use, they would like to see further research conducted on the topic. “I think the study needs to be confirmed by other centers, possibly with a larger number of computer users,” says Dr. Stevens. “I think more study is needed of this question.” The Mayo Clinic study was conducted with employees identified to be heavy computer users at Mayo Clinic in Scottsdale, Ariz. “We chose Mayo Clinic employees because we knew we could find out who were computer users at our medical center,” says Dr. Stevens. “We have a large number of secretaries and people who do transcription and patient accounts billing. All of those are occupations that make heavy use of a computer, so we had our own ready-made study group right in our own facility.” The investigators sent surveys to 314 employees inquiring about hand numbness and sensations of “pins and needles,” common symptoms of carpal tunnel syndrome. Of the 257 people who responded to the survey, those who indicated symptoms suggestive of carpal tunnel syndrome were invited to a clinical study unit for an interview and completion of further questionnaires. Unless these patients were clearly diagnosable with a condition other than CTS, they were tested for CTS via electromyogram (EMG), or a nerve conduction study. Only 27, or 10.5 percent, of the participants met clinical criteria for CTS, and in nine, or 3.5 percent, EMG confirmed the syndrome. Though the researchers did not discover CTS in a high percentage of the participants, other conditions potentially linked to the office work environment were present in a larger number of participants. “There were about 30 percent of our employees surveyed who had tingling of various sorts in the hand, but only 10.5 percent of them turned out to have carpal tunnel syndrome,” says Dr. Stevens. “They had tingling from involvement of other nerves and a variety of symptoms that are likely not clinically significant. The vast majority of the people who had tingling in the hand but didn’t have carpal tunnel syndrome did not have any serious illness as far as we could determine. A few of them had what is called an ‘ulnar neuropathy,’ which relates to another nerve in the hand, a few of them had pinched nerves in the neck, and a lot of them had rather mild and nondescript tingling that really did not mean much clinically.” For those who suspect that they may have problems in their hands, Dr. Stevens suggests consulting one’s family physician first, who would then make a decision about obtaining nerve conduction studies or perhaps refer to a hand clinic or surgeon for further evaluation. Research suggests that one person in 10 will develop symptoms of CTS over a lifetime. CTS is a compression of the median nerve at the wrist, leading to numbness tingling and pain in the hand. The median nerve passes through the carpal tunnel at the wrist and into the palm where it sends branches that control feeling to the thumb, index, middle and part of the ring fingers. Symptoms of CTS include tingling, pain or numbness in the hand and fingers. “It’s typically worse with reading a newspaper or book, talking on the phone or driving a car, and frequently it wakes people up in the middle of the night with tingling or pain in the hand,” says Dr. Benn Smith, co-author of the study and neurologist at Mayo Clinic Scottsdale. “Very often, people obtain temporary relief by shaking the hand or rubbing it, causing the numbness and tingling to go away.” CTS is treated by wearing a splint at night to reduce waking up or by an injection of cortisone to reduce swelling. If these measures are not successful, carpal tunnel release surgery, which sections the tough transverse carpal ligament and relieves pressure on the median nerve, may be performed. Other resources for journalists: Neurology web site: http://www.neurology.org/ Another point of view: 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 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 [2] from the early 1990s, the other is a more recent Swedish study [3]. 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 foreseeable future. · 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. [4] 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 [5] 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 [6]. Occupational risk factor most strongly associated with medically called CTS were: o exposure to repetitive bending/twisting of the hands/wrists at work (OR = 5.2) o race (OR = 4.2; whites higher than nonwhites) o gender (OR = 2.2; females higher than males) o use of vibrating hand tools (OR = 1.8) o 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 symptoms [7]. · 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 prevlance 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 syndrome. · 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 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 already noted. What's even worse is that Gov. Locke of Washington State is now calling for that state to repeal it's ergonomics regulation because he asserts that the Mayo clinic "proves" that ergonomics is unnecessary, and that assertion too is flawed! 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 posture. For information on how to arrange a computer workstation for neutral posture working see the adult workstation guide and the HealthyComputing.com web site. References 1. 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. 2. 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. 3. Atroshi, I., Gummessons, C., Johnsson, R., Ornstein, E., Ranstam, J. and Rosén, I. (1999) JAMA, 282 (2) 153-158. 4. Nordstrom, D. L., F. DeStefano, et al. (1998). Incidence of diagnosed carpal tunnel syndrome in a general population. Epidemiology 9 (3): 342-5. 5. Franklin, G. M., J. Haug, et al. (1991). "Occupational carpal tunnel syndrome in Washington State, 1984-1988." Am J Public Health 81(6): 741-6. 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. 7. http://danke.com/Orthodoc/carpaltunnel.html