Common
Injuries
Ergonomic injuries are widely recognized as a major factor
in work place health. About one-third of all occupational injuries and
illnesses stem from over exertion and/or repetitive motion.
Carpal Tunnel Syndrome (CTS), according to the U.S. Department
of Labor Occupational Safety & Health Administration (OSHA), results
in more days on average away from work than any other workplace injury.
The median number of days away from work for CTS is 25 days, compared
to 17 days for fractures, and 20 days for amputations. Workers with severe
injuries can face permanent disability that prevents them from returning
to their job or handling simple everyday tasks. The act of picking up
a child, or even pushing a shopping cart, can become a painful experience.
The most common cause of Carpal Tunnel Syndrome is inflammation
of the tendons in the carpal tunnel which can be attributed to repetitive
use of the hand and/or wrist in awkward positions. Although there are
no epidemiologic studies that identify the dose-response relationship
of posture to risk, several studies have shown that wrist flexion/extension,
ulnar/radial deviation and forearm supination/pronation does modify carpal
tunnel pressure. Other studies have indicated that fluid pressures of
40-50mmhg sustained for 60 minutes can cause transient changes in nerve
function while additional studies have indicated that elevated carpal
tunnel pressure can cause more prolonged effects on tissue1. Although
a critical pressure-time threshold associated with CTS has yet to be determined,
the pressure is likely to be below the critical threshold apparent for
acute median neuropathy, which is approximately 30mmHg2, 3. Clearly, in
order to reduce the risk of CTS while pipetting, individuals should maintain
neutral forearm and wrist positions that cause the least amount of pressure
on the carpal tunnel while pipetting.
Contributing Factors:
Forearm supination and pronation
Effects of forearm pronation and supination
on carpal tunnel pressure
Data comparing the use of different pipettes
and the associated forearm
rotation during pipetting
Wrist flexion and extension
Data comparing the use of different pipettes
and the associated wrist
extension and flexion during pipetting
Wrist radial and ulnar deviation
Data comparing the use of different pipettes
and the associated wrist
radial and ulnar deviation during pipetting
1. Rempel D, Bach, J, Gordon L, So, Y. Effects of Forearm
Pronation/Supination on Carpal Tunnel Pressure. J. Hand Surg 1998; 1:38–42
2. Gelberman RH, Hergenroeder PT, Hargens AR, Lundborg
GN, Akeson WH. A study of carpal canal pressures. J Bone Joint Surg 1981;
63A:380–383
3. Lundborg G, Gelberman RH, Minteer-Convery M, Lee YF,
Hargens AR. Median nerve compressioin in the carpal tunnel: functional
response to experimentally induced controlled pressure. J. Hand Surg 1982;
7:252–259
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What
is forearm supination and pronation?
Forearm supination is movement of the forearm causing
the hand to be positioned in a “palm up” posture. Forearm
pronation is movement of the forearm causing the hand to be positioned
in a “palm down” posture. Forearm rotation during pipetting
is common with axial designed pipettes. As illustrated, pipettes
are often rotated, causing the hand to be positioned “palm
up” (supination) and the wrist bent backwards. This is a common
posture when attempting to maintain the elbow close to the body
or rest it on the work surface. This is also a common posture that
results when a user attempts to rotate the pipette out of their
line of sight so they can accurately position a tip into a well
on a microtiter plate.
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Effects of forearm supination and pronation
on carpal tunnel pressure
Repetitive twisting of the forearm between the palm up
and palm down positions (supination and pronation of the forearm) throughout
the pipetting task, as well as wrist flexion and extension increases the
fluid pressure. A recent study measured the effects of forearm supination/pronation
on carpal tunnel pressure found that carpal tunnel pressure was at its
lowest when the forearm is maintained at 45° pronation. The extension/flexion
and ulnar/radial deviation postures associated with the lowest carpal
tunnel pressure cited a forearm rotation angle near 45° pronation.
Although a critical pressure-time threshold associated with CTS has yet
to be determined, the pressure is likely to be below the critical threshold
apparent for acute median neuropathy, which is approximately 30mmHg.
The published article from the study appears in the Journal
of Hand Surgery, Volume 23A – Number 1, further states “This
set of postures should be considered during the design of hand-intensive
tasks and hand tools in order to minimize carpal tunnel pressure during
repetitive activities.”
(This article is available on request in the Ergonomics/Training
Resources area of this web site, or by clicking
this link)
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Is
there data comparing the use of different pipettes and the associated
forearm rotation during pipetting?
Ergonomic
Technologies Corporation, an independent consulting firm specializing
in workplace ergonomics, conducted a series of tests using traditional
axial-designed pipettes and VistaLab Technologies’ new Ovation
BioNatural Pipette. Electromyogram testing (EMG) was used to measure
the activity of muscle groups and degrees of rotation during various
pipetting tasks. (Electromyography (EMG) studies the function of
individual nerves and muscles and includes measurement of nerve
and muscle response to electrical stimulation and measurement of
spontaneous muscle electrical activity) The testing revealed that
the Ovation pipette showed a significant reduction in forearm rotation
and wrist flexion during use when compared to other pipettes. The
Ovation pipette’s shape and operating position reinforce ergonomically-correct
pipetting by encouraging the user’s hand, wrist, and arm to
assume the neutral postures near 45° pronation recommended by
ergonomic experts.
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What
is wrist flexion and extension?
Wrist
extension is the upward movement of the wrist to which results in
the palm facing outward, while wrist flexion is the downward or
inward movement of the wrist which results in the palm facing inward
(see illustration below). Both movements reduce available strength,
however flexion can cause up to 55% reduction in strength at just
25° of motion from a neutral position. |
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Is there data comparing the use of different pipettes
and the associated wrist flexion and extension during pipetting?
Ergonomic
Technologies Corporation, an independent consulting firm specializing
in workplace ergonomics, conducted a series of tests using traditional
axial-designed pipettes and VistaLab Technologies’ new Ovation
BioNatural Pipette. Electromyogram testing (EMG) was used to measure
wrist flexion and extension during pipetting. . (Electromyography
(EMG) studies the function of individual nerves and muscles and
includes measurement of nerve and muscle response to electrical
stimulation and measurement of spontaneous muscle electrical activity)
While average wrist extension was similar for all pipettes during
an uninterrupted pipetting cycle, average wrist flexion when using
axial-designed pipettes exceeded the recommended limits supported
in published literature. This contributes to muscle fatigue which
can lead to musculoskeletal injury.
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What
is wrist radial and ulnar deviation?
Radial
and ulnar deviation is the side-to-side movement of the hand at
the wrist, toward or away from the thumb. Radial deviation causes
up to a 20% reduction in hand strength with just 25 ° of motion
from a neutral position. At 40% Ulnar deviation a similar drop in
available strength is observed (see illustration). |
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Is there data comparing the use of different pipettes
and the associated radial and ulnar deviation during pipetting?
Ergonomic
Technologies Corporation, an independent consulting firm specializing
in workplace ergonomics, conducted a series of tests using traditional
axial-designed pipettes and VistaLab Technologies’ new Ovation
BioNatural Pipette. Electromyogram testing (EMG) was used used to
measure wrist radial and ulnar deviation during pipetting. . (Electromyography
(EMG) studies the function of individual nerves and muscles and
includes measurement of nerve and muscle response to electrical
stimulation and measurement of spontaneous muscle electrical activity)
While there was little difference observed in ulnar deviation among
all pipettes, a significant difference in radial deviation was observed
between the Ovation BioNatural Pipette and the traditional axial-designed
pipettes. As noted earlier, increased radial deviation reduces hand
strength and can result in fatigue. |
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