Latest Thinking on Computer-Related Pain by David M Rempel

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The Latest Thinking on Computer-Related Pain

September 19, 2008


Dr. David M. Rempel is an occupational medicine physician at the University of California, San Francisco, and a professor of bioengineering at the University of California, Berkeley. He is also director of the ergonomics research laboratory at the University of California.

Q: Since the late 1980s, there has been much controversy over whether typing on a computer or other repetitive workplace activities could cause repetitive strain injuries of the hand, arm and shoulder. Has that debate been settled?

A: There has been some settling of the issue. It is pretty clear that jobs that involve high-force hand activities and repetitive hand motions — such as in manufacturing or heavy industry or meatpacking — are associated with wrist tendinitis and carpal tunnel syndrome and other arm disorders. Many companies have been making efforts to modify their workplaces to reduce those loads, and they have had some effectiveness in reducing injuries in the workplaces.

But there is still some controversy in the scientific community about whether keyboard and mouse use causes carpal tunnel syndrome.

Q: What is known about carpal tunnel syndrome and computer use?

A: Recent research indicates that the risk of carpal tunnel syndrome, when using the keyboard for less than 20 hours a week, is relatively low or nonexistent. That's a new finding that has emerged over the past 10 years.

What is still missing is an understanding of what happens when people use the computer keyboard for more than 20 or 30 hours a week for many years. There, the question of carpal tunnel syndrome and keyboard use is still unanswered.

What is also interesting is that in the last few years, strong evidence has emerged that if you use a computer mouse for more than 20 hours a week, your risk of carpal tunnel syndrome is increased. It looks like the mouse may be more problematic than the keyboard, at least for carpal tunnel syndrome. And mouse use is also associated with elbow and shoulder problems.

Q: Many researchers have shifted away from using the term ”repetitive strain injury.” Why is that?

A: Well, the term “repetitive strain injury” has embedded within it the concept that repetition is the cause. But the actual cause may not be repetition per se; it might be prolonged finger loads or static forces or high forces. And so the use of the term has largely been replaced by specific diagnoses that are more exact — carpal tunnel syndrome or wrist tendinitis. Or researchers use a more generic term like musculoskeletal disorder.

Q: Why is it that some people develop these musculoskeletal illnesses when friends or colleagues who are doing exactly the same activities do not?

A: That's a great question. It may have to do with a difference in their workload. Some people may have a higher hand workload than others. It may have to do with the way they do their work; they may apply larger forces when performing the same task, or forces for longer durations.

If you look at people who do identical hand activities, there's a slightly increased risk for women than men. This difference is probably due to the relative lower strength of women than men. There are also differences in hand-intensive activities that they do at home or outside of work.

In addition, there may be some personal factors that put a person more at risk: for example, obesity and medical conditions like diabetes.

Q: How good is the evidence that treatments are effective for musculoskeletal disorders?

A: We know that for carpal tunnel syndrome the use of wrist splints, injections of corticosteroids into the wrist, surgery and to some extent ultrasound therapy are effective. There's not much data to support physical therapy modalities such as hot and cold treatments and stretching maneuvers for carpal tunnel syndrome.

For tendinitis, there's much less data about what is effective and what is not. We don't have enough randomized controlled trials that demonstrate a strong effectiveness of treatments. But for some types of tendinitis — such as localized extensor and flexor tendinitis of the wrist, for trigger finger and for tennis elbow — splints and corticosteroid injections are helpful.

With iontophoresis and phonophoresis — methods of delivering drugs into the tissue by applying an electrical charge across the skin — evidence for their effectiveness, based on randomized controlled trials, does not exist at this point, for either carpal tunnel syndrome or tendinitis.

Q: Does that mean that these treatments aren't effective, or does it just mean there's a gap in the research evidence base?

A: There is primarily a research gap.

Q: Then how do clinicians determine the best way to treat their patients?

A: There are guidelines published by the American College of Occupational and Environmental Medicine and the American Academy of Orthopaedic Surgeons for the management of these disorders. Clinicians need to read the medical literature, check the guidelines. That's the typical way that physicians keep up with all knowledge.

Q: A few years ago, you and a group of colleagues published a systematic review of the scientific evidence on the effectiveness of the different workplace interventions for preventing repetitive strain problems from computer use. And you are just now finishing a second review. Based on your analyses, what ergonomic interventions really help?

A: There are only a few items that appear to be effective. It appears that the alternative split keyboards and some types of computer mice can help people who already have hand problems, and may also prevent musculoskeletal problems. There is also evidence that taking five-minute breaks from computer use, at least every hour, can reduce pain. And that forearm supports, not wrist supports, placed in front of the keyboard can reduce pain.

Q: What is the latest thinking on the safest postures for working at the computer?

A: There is this traditional recommendation that people sit at 90-degree angles: their hips at 90 degrees, elbows at 90 degrees and so on. That posture recommendation has not been shown to be useful in preventing musculoskeletal problems.

What appears to be useful is a sitting posture where you are more reclined, and your chair back support is about 15 degrees from vertical, so that you can lean back. Your keyboard should be positioned relatively low, near the elbow height. Your wrists should be relatively straight when you're using a keyboard or mouse. Use a forearm support or a thin keyboard to prevent wrist extension (bending upward).

Q: Why is it better to lean back in your chair?

A: When you lean back, you transfer the load from your upper body to the back of the chair, rather than having the whole weight of your upper body going through your spine, which happens when you sit upright. The reality is that people cannot sit in a vertical for very long. Their trunk muscles become fatigued.

Q: Where did that earlier posture recommendation come from?

A: I think from Germany. They were really into 90-degree angles. But there is little physiologic basis for that recommendation.

Q: You've done research testing the benefits of a forearm support board in computer users. Tell us about it.

A: There's some evidence that forearm support might prevent shoulder pain, because it unloads the shoulders so that they are not supporting your arm weight when you're using the keyboard for long durations. We wanted to replicate those earlier studies.

So we did a one-year prospective, randomized, controlled trial of 182 employees at a customer service call center in Northern California. We randomized the employees into four groups and tested a different mouse, a forearm support and a combination of the two. We found that forearm support reduced the risk of shoulder injuries and shoulder pain.

The average score for neck/shoulder pain was about 2.5 on a scale of 0 to 10. With arm support, the pain reduction was about half a point. Furthermore, about half of the usual shoulder injuries were prevented by the forearm support. There was also some reduction in right forearm and wrist pain, but not as much as with the shoulder.

Q: So how do computer users get forearm support at their work station?

A: The simplest way is to adjust the work surface to the level of your elbow, or a little above that, and then move the keyboard away from the front edge of the work surface so you can rest your forearms on the surface. If you're using a thin keyboard, which we recommend, then you don't have very much wrist extension.

The second way is to attach a forearm support board, like the one we tested in the study, to the front edge of your work surface. The one we tested was a Morency Board by R&D Ergonomics. (They did not fund our study.)

The third way is to adjust your chair arm rests so that they provide forearm support, but this requires a chair with arm rests that adjust in height and location.

Q: Does following these types of ergonomic recommendations solve a patient's problems for sure?

A: No. However, in general, my experience is that following the recommendations, like the ones we've just talked about, will help. In some people it will completely resolve their symptoms. But in others, it won't solve the problem, especially if we have not accurately diagnosed what is wrong. For instance, if the patient has a neck problem from a nerve that's pinched in the cervical region of the spine, making these ergonomic changes probably will not help.

In such cases, I'd revisit the patient's history and repeat the physical examination to make sure the diagnosis is accurate. For some diagnoses, such as neck- and shoulder-related problems, physical therapy is extremely valuable.

Keyboard Ergonomics