Carpel Tunnel Syndrome
Reprinted from the University Computing Times, July-August 1990, pages 17-19.
Copyright © 1990, Trustees of Indiana University. All rights reserved.
Avoiding Carpal Tunnel Syndrome
A Guide For Computer Keyboard Users
By Mark Sheehan
Carpal tunnel syndrome is common among computer keyboard users. It can
strike anyone, and its consequences are serious. Awareness of the
problem and its causes is crucial to preventing CTS. With proper
ergonomics and attention to the work routine you can prevent CTS; with
early detection and treatment it need never become debilitating. The
employer's attention to stress levels, proper ergonomics, and the early
warning signs of CTS are important in keeping the ailment at bay in the
Carpal tunnel syndrome (CTS) is a painful, debilitating condition. It
involves the median nerve and the flexor tendons that extend from the
forearm into the hand through a "tunnel" made up of the wrist bones, or
carpals, and the transverse carpal ligament. As you move your hand and
fingers, the flexor tendons rub against the sides of the tunnel. This
rubbing can cause irritation of the tendons, causing them to swell. When
the tendons swell they apply pressure to the median nerve. The result
can be tingling, numbness, and eventually debilitating pain.
CTS affects workers in many fields. It is common among draftsmen, meat cutters, secretaries, musicians, assembly-line workers, computer
users, automotive repair workers, and many others. CTS can be treated
with steroids, anti- inflammatories, or physical therapy, or with
surgery to loosen the transverse carpal ligament. Recovery of wrist and
hand function is often, but not always, complete.
Like many musculoskeletal disorders, CTS has a variety of causes. It is
most often the result of a combination of factors. Among these are:
- Genetic predisposition. Certain people are more likely than others to
get CTS. The amount of natural lubrication of the flexor tendons varies
from person to person. The less lubrication, the more likely is CTS. One
study has related the cross-sectional shape of the wrist, and the
associated geometry of the carpal tunnel, to CTS. Certain tunnel
geometries are more susceptible to tendon irritation.
- Health and lifestyle. People with diabetes, gout, and rheumatoid
arthritis are more prone than others to develop CTS, as are those
experiencing the hormonal changes related to pregnancy, menopause, and
the use of birth control pills. Job stress has also been linked to an
increased likelihood of CTS. And CTS seems to be more frequent among
- Repetitive motion. The most common cause of CTS that has been attributed
to the workplace is repetitive motion. When you flex your hand or
fingers the flexor tendons rub against the walls of the carpal tunnel.
If you allow your hand time to recover, this rubbing is not likely to
lead to irritation. The amount of recovery time you need varies from
fractions of a second to minutes, depending on many circumstances,
including the genetic and health factors mentioned above, as well as the
intensity of the flexing, the weight of any objects in your hand, and
the extent to which you bend your wrist during flexing.
- Trauma. A blow to the wrist or forearm can make the tendons swell and
cause or encourage the onset of CTS.
Computer keyboard users can take several steps to lower their chances of
developing CTS. Some of these center around the configuration of the
workplace, or "ergonomics." Others have to do with human factors.
- Ergonomics. Proper seating is crucial to good ergonomics. The height of
your seat and the position of your backrest should be adjustable. The
chair should be on wheels so you can move it easily. Arm rests on the
chair, though optional, are often helpful.
- Table height. To adjust the chair properly, look first at the height of
the table or desk surface on which your keyboard rests. On the average,
a height of 27-29 inches above the floor is recommended. Taller people
will prefer slightly higher tables than do shorter people. If you can
adjust your table, set your waist angle (see below) at 90 degrees, then
adjust your table so that your elbow makes a 90 degree angle when your
hands are on the keyboard.
- Wrist angle. If your keyboard is positioned properly your wrists should
be able to rest comfortably on the table in front of it. Some keyboards
are so "thick" that they require you to bend your hands uncomfortably
upward to reach the keys. If so, it will help to place a raised wrist
rest on the table in front of the keyboard. A keyboard that requires you
to bend your wrists is a common cause of CTS among computer users.
- Elbow angle. With your hands resting comfortably at the keyboard and
your upper arms vertical, measure the angle between your forearm and
your upper arm (the elbow angle). If it is less than 90 degrees, raise
the seat of your chair. If the angle is greater than 90 degrees, lower
the seat. Try to hold your elbows close to your sides to help minimize
"ulnar displacement" the sideways bending of the wrist (as when reaching
for the "Z" key).
- Waist angle. With your elbow angle at 90 degrees, measure the angle
between your upper legs and your spine (the waist angle). This too
should be about 90 degrees. If it is less than 90 degrees, your chair
may be too low (and your knees too high). Otherwise, you may need to
alter the position of the backrest or adjust your own posture (nothing
provides better support than sitting up straight). (Note: If making your
waist angle 90 degrees changes your elbow angle, you may need to
readjust the height of your chair or table.)
- Feet. With your elbows and waist at 90 degree angles, your feet should
rest comfortably flat on the floor. If they don't, adjust your chair and
table height and repeat the steps above. If your table isn't adjustable
and your feet don't comfortably reach the floor, a raised footrest can
help. Otherwise, you may need a different table.
You need very little recovery time between keystrokes to cool and
lubricate the flexor tendons. If you type constantly, however, the need
for recovery builds. Further, working with your hands bent upward at the
wrists or frequently bending your wrists sideways heightens the friction
within the carpal tunnel. It takes longer to recover from these motions.
Working under stress (deadline pressure, anger, or other anxiety) can
make matters even worse. Many studies recommend a 10-15 minute break
each hour to give yourself the recovery time you need. This needn't be a
break from productive activities just a break from your keyboard. Exercises
can help, too. Try the following:
- Make tight fists, hold for one second, then stretch your fingers out
wide and hold for five seconds. Repeat several times.
- With arms outstretched in front of you, raise and lower your hands
several times. Rotate your hands ten times (make circles in the air with
Variety is the key. CTS occurs most frequently in workers whose motions
are not only repetitious but are kept up for hours at a time. If you use
a keyboard, structure your workdays to include a mix of activities each
hour. For example, instead of typing all morning and filing all
afternoon, mix typing and filing throughout the day.
The most painful cases of CTS are those that have gone undetected or
untreated over a long time. CTS can be caught easily in its early
stages, however, and much of the pain and all of the disability avoided.
Early symptoms include a tingling in the fingers, often beginning
several hours after work activity has stopped. Because of this delay in
the appearance of symptoms, many CTS sufferers don't make the connection
between their work activities and the pain they feel until it's too
late. The tingling can lead, over time, to stiffness and numbness in the
fingers and hand, and then to severe wrist and hand pain.
For many individuals the early symptoms of CTS go unnoticed. Employers
and co-workers can help one another identify the onset of CTS by
watching for and pointing out any unconscious shaking of the hands,
rubbing of the wrists, or unusual postures or hand positions at the
keyboard. At the first sign of CTS, you should be examined by a doctor who
specializes in hand and wrist disorders. The doctor can perform a number
of simple tests to detect CTS, and can prescribe specific steps for
avoiding the problem.