International Journal of Occupational Safety and Ergonomics (JOSE) 2007, Vol. 13, No. 1, 29–38
Carpal Tunnel Syndrome in Occupational
Medicine Practice
Joanna Bugajska
Anna Jędryka-Góral
Iwona Sudoł-Szopińska
Department of Ergonomics, Central Institute for Labour Protection
– National Research Institute, Poland
Kazimierz Tomczykiewicz
Department of Neurology, Military Institute of the Health Services, Poland
Work-related overload syndromes are chiefly associated with the upper limbs, where carpal tunnel syndrome
(CTS) plays a leading role. This article analyses methods of diagnosing CTS, with special emphasis on those
that can be used by physicians in early diagnosis of CTS in workers doing monotonous work. It also discusses
occupational (e.g., assembly work, typing, playing instruments, packaging and work associated with the use
of a hammer or pruning scissors) and extra-occupational factors (e.g., post-traumatic deformation of bone
elements of the carpal tunnel, degenerative and inflammatory changes in tendon sheaths, connective tissue
hypertrophy or formation of crystal deposits) leading to CTS; diagnostic methods (subjective symptoms,
physical examination, manual provocative tests, vibration perception threshold, electrophysiological
examination and imaging methods); and therapeutic and preventive management tools accessible in
occupational medicine practice.
carpal tunnel syndrome
diagnostic methods
1. INTRODUCTION
Musculoskeletal disorders (MSDs) are the most
frequent causes of chronic pain, absence from work
and disability leading to temporary or permanent
incapacity to work. In recent years diseases
of the musculoskeletal system and connective
tissue constituted the basis of the second greatest
number of certificates confirming total inability
to work issued in Poland. In total, in 2000, 14 934
certificates (15.4% of all certificates) and in
2001, 11 064 certificates (13.3%) resulted from
occupational medicine
those diseases [1]. It is estimated that in the USA,
13.9–15% of the population have MSDs [2, 3].
The extent and significance of the problem of
MSDs may be confirmed by the fact that the World
Health Organization (WHO) declared 2000–2010
a Bone and Joint Decade. Those work-related
MSDs, which are defined as overload syndromes,
pose a special problem to occupational medicine
professionals. Additionally, chronic degeneration
and inflammatory diseases of the loco-motor
system require not only significant expenditure
on treatment, rehabilitation and welfare, but most
This paper has been prepared as part of task 3.A.01 of the National Programme “Adaptation of Working Conditions in Poland to
European Union Standards”, partly supported—within the scope of research and development—in 2002–2004 by the State Committee
for Scientific Research of Poland. The Central Institute for Labour Protection – National Research Institute was the Programme’s main
co-ordinator.
Correspondence and requests for offprints should be sent to Joanna Bugajska, Department of Ergonomics, Central Institute for Labour
Protection – National Research Institute, Czerniakowska 16, 00-701 Warszawa, Poland. E-mail: <jobug@ciop.pl>.
30
J. BUGAJSKA ET AL.
of all they lead to the deterioration of the quality
of life and to incapacity to work [4]. This is
particularly important in view of the ageing of
the populations in many developed countries,
including Poland, caused primarily by the
extension of human life. Work-related overload
syndromes are predominantly associated with
upper limbs. Nine point four percent of the MSDs
of the upper limbs are located in the area of hands
and wrists. The carpal tunnel syndrome (CTS)
accounts for 1.5% of those; 0.4% are caused by
tendenitis [5].
Symptoms of these syndromes, of CTS
in particular, belong to the leading factors
in decreasing mobility and independence in
everyday life. They affect the quality of life in the
“third age”, defined as the period of 10–30 years
after retiring [6, 7, 8]. According to Ilmarinen [7],
on the one hand, work environment factors impair
the quality of life measured with limitations
in everyday activities and, on the other, the
quality of life in the third age may be raised by
improving working conditions during the period
of professional activity. These conclusions, based
on a longitudinal, multi-year study carried out
on the Finnish workforce, pose a challenge to all
who deal with safety and health at work.
The authors of the present paper assume that a
broader dimension of the problem is inevitable
and they would like to stress the importance of
illness prevention in the ever-growing number of
elderly people and of activities aimed at reducing
risk factors at work and early diagnosis of the
syndrome of upper limb overload.
Therefore the aim of this article is to analyse
the methods of diagnosing CTS with special
emphasis on those that can be used by physicians
in early diagnosis of CTS in workers doing
monotonous work.
2. FACTORS CAUSING CTS
CTS is a neuropathy caused by a compression
of the median nerve in its passage through the
carpal tunnel [9. 10]. The basic clinical symptoms
include pain, numbness and paraesthesia in the
median nerve. In addition, there are symptoms
of damage also to the motor part of this nerve.
JOSE 2007, Vol. 13, No. 1
The causes of CTS may be general or local. In
general disorders, the cause of this neuropathy
is the tightness in the carpal tunnel which occurs
during increased tissue pressure due to, e.g.,
connective tissue hypertrophy or formation of
crystal deposits. The causes include hormonal
disorders (acromegalia and hypotyreosis),
pregnancy and menopause, metabolic diseases
(diabetes, amyloidosis, obesity, pseudogout
and mucopolysaccharidosis), diseases of blood
vessels (arterial hypertension, Raynaud’s disease
and median artery thrombosis) and others
(allergic reaction) [11, 12].
The local causes of CTS include posttraumatic deformation of bone elements of the
carpal tunnel, deep postburn scars, degenerative
and inflammatory changes in tendon sheaths,
malformations in muscles, bones and vessels in
the wrist joint, tumours and paratumours, and
mycotic lesions.
CTS is one of the most frequent work-related
locomotor system disorders and is more frequent
in persons whose work or hobby requires
repetitive actions, application of significant force
and uncomfortable position of the wrist and hand.
CTS incidence tends to increase with age and the
number of working years; the syndrome is more
often found in women than in men [13, 14].
The significance of the musculoskeletal system
overload in the etiology of the syndrome is
exemplified by its increased incidence in persons
with paraplegia, who live in a wheelchair, as
compared to the population without this disability
[15].
Typical occupational activities causing the
said problems include grinding, polishing, sandblasting, assembly work, typing, counting money,
playing instruments, using surgical instruments,
packaging, cooking, butchering, washing by
hand, scrubbing, typing, computer work, work
associated with the use of a hammer or pruning
scissors and the like [13, 16, 17, 18, 19, 20, 21].
Factors associated with work (high repetitiveness
of movements, the force used and an awkward
position of the hand) may lead to muscular fatigue
and discomfort in the carpal area; these conditions
will abate quickly if the interval between such
activities is sufficiently long. However, when
CTS IN OCCUPATIONAL MEDICINE PRACTICE
work is continued despite fatigue, there may be
symptoms of tendonitis and swelling in the carpal
tunnel, resulting in an increased compression of
the tunnel [22]. The pressure increase in the carpal
tunnel is accompanied by perfusion disturbances
and also a mechanical compression of the median
nerve, which causes symptoms of irreversible
damage [5, 23, 24].
3. DIAGNOSTICS PROCEDURE
Any delay in diagnosis and treatment may lead
to irreversible damage to the median nerve,
persistent ailments and, as a result, to total
inability to work. Early treatment of CTS is likely
to bring about total recovery.
The classic diagnostic procedure for CTS is
based on the following steps [25, 26]:
1. carefully taken medical history focused on
such symptoms as numbness and tingling
or pain in the area innervated by the median
nerve;
2. physical examination with the use of
provocative tests (Tinel’s sign and Phalen’s
manoeuvre) and determination of the vibration
perception threshold;
3. median nerve conduction velocity test.
Imaging of the spatial structure of the carpal
tunnel can be helpful, in particular in differential
diagnosis.
In practice, the conditions connected with the
compression of the median nerve are sometimes
hard to determine. Most patients who complain
of pain and tingling in the entire arm and forearm
have difficulties with locating and determining
the nature of these conditions. They are not,
in particular at the initial stage of the illness,
so specific as to guide diagnostic procedure
accurately from the very onset. This results in
a delay in taking appropriate preventive and
therapeutic measures.
On the basis of published clinical experience, a
group of researchers reached an agreement on the
following issues:
• There is no perfect gold standard for
CTS diagnosis. Although findings of
31
electrodiagnostic studies are considered to be
the most accurate single tests, false negatives
and positives of those findings are well
documented.
• A combination of electrodiagnostic studies
and characteristic symptoms provides the
most accurate diagnosis. Findings of physical
examinations add little diagnostic value if
electrodiagnostic findings and characteristic
symptoms are available.
• In the absence of electrodiagnostic findings,
combinations of characteristic symptoms and
findings of physical examinations provide the
greatest diagnostic information [27].
In their daily practice, occupational medicine
physicians taking care of persons performing
repetitive manual work, often meet workers
complaining of ailments in their upper limbs.
That is why, when suspecting CTS, the physician
must decide whether the affected person has
symptoms of short-lived work overload only or
full symptoms of the syndrome.
In any case of suspicion that the pathological
changes found are related to professional
activities, it is necessary to perform an ergonomic
analysis of the workplace of the affected person,
i.e., assess the work process taking into account
the type of tasks performed by the worker, the
posture, repetitiveness rate for working tasks and
the length of exposure. Although, in many cases
these situations are hard to assess, there are cases
in which this analysis should be performed by
occupational safety and health (OSH) specialists,
as a step before the occupational medicine
physician’s counselling. In addition, unlike in the
case of harmful agents identified in the working
environment, occupational medicine does not
have any hygienic standards to determine safe
working conditions in respect of locomotor
system overload. That is why workplace analysis
frequently relies on expert knowledge and
judiciary practice. In those cases ergonomic
standards for the organization of the workplace
and its assessment could be applied (e.g.,
directives, ISO standards, recommendations).
Also indispensable in identifying CTS are
preventive entrance medical examinations and
preventive periodic medical examinations.
JOSE 2007, Vol. 13, No. 1
32
J. BUGAJSKA ET AL.
Methodological guideline concerning the
frequency and scope of preventive examination of
workers, contained in Annex 1 to the Regulation
of the Polish Minister of Health and Social
1
Welfare , provide for such examination in the
case of work with video display units (VDU), in
a forced body posture, and requiring monotypic
limb movements.
In practice, preventive examination of the
musculoskeletal system consists of a careful
investigation of a history concerning the
occurrence of subjective complains (pain,
numbness and impairment of motor functions)
and analysis of sick-leave periods. At this stage
no additional routine examination is carried out.
4. DIAGNOSTIC METHODS
4.1. Clinical Examination
Clinical examination, which consists of the
history, self-administered investigation of
subjective symptoms, physical examination
and manual provocative test procedure is still a
very valuable method used in diagnozing CTS,
especially in preventive practice.
4.1.1. Subjective symptoms
A diagnosis of a classic form of the syndrome
does not present many difficulties. Symptoms
may occur bilaterally, but usually they occur in
the dominant hand. They include pain, numbness
and paraesthesia in the median nerve area, i.e., in
the range of the thumb, index finger and middle
finger as well as the radial side of the ring finger.
The symptoms do not apply to the little finger.
Those ailments typically arise or intensify when
things are done with a bent wrist and at night.
Ailing people wake up, have to move their body
and their hand several times for the symptoms
to abate (brachialgia parestetica nocturna). In
the morning hours fingers seem to be swollen,
stiff and clumsy. At this stage there is usually no
motor dysfunction or it is insignificant. At the
final stage, the motor part of the median nerve
is damaged, leading to paresis and muscular
atrophy. When giving their medical history,
patients report impaired hand function, difficulties
with twisting off a jar lid, dropping small objects
and other manifestations of motor disorders.
The subjective symptoms of the syndrome are
nonspecific. They occur much more frequently
than CTS is diagnozed on the basis of objective
tests. According to Atroshi, Gummesson,
Johnson, et al., if reported subjective symptoms
are analysed, CTS is found in more than 14%
of the subjects, while if electrophysiologic
examination is used, the syndrome is diagnosed
only in 2.7% of them [28]. Basing on the
examination covering a wide population, Tanaka,
Wild, Seligman, et al. estimated that only about
a third of all persons reporting subjective CTS
symptoms (more than 1.8 million) are clinically
confirmed [5].
The following criteria have been used in
epidemiological studies on the occurrence of
CTS, established on the basis of subjective
symptoms [14, 29, 30]:
• the occurrence of at least two of three
symptoms of damage to the motor part of
the median nerve (a tendency to drop small
objects, difficulties with twisting off a jar lid
and picking up objects and decreased grip
strength);
• the occurrence of at least one of three
symptoms of damage to the sensory part of
the median nerve (numbness in the hand or
fingers; pain in the forearms, hand or fingers;
or any of these symptoms occurring at night).
To assess the grade of individual symptoms
reported by a patient the VAS (visual assessment
scale) is useful, whereas to determine localization
of these symptoms different diagrams of the
upper limbs are in use.
According to studies performed by Franzblau,
Salerno, Armstrong, et al., the reliability of
1
Regulation of the Minister of Health and Social Welfare of May 30, 1996, on carrying out medical examinations of workers, the
scope of preventive health care and medical certificates issued for the purposes listed in the labour code]. Dz U. 1996;(69):item 332.
In Polish.
JOSE 2007, Vol. 13, No. 1
33
CTS IN OCCUPATIONAL MEDICINE PRACTICE
questionnaires used to assess information related
to musculoskeletal symptoms among industrial
workers appears to be good to excellent [31].
However symptom surveys collect information
that are subjective in nature and have potential
to be influenced by psychosocial factors (i.e.,
organization of work and job satisfaction).
Katz and Stirrat created a method for CTS
diagnosis based on a self-administered hand
diagram in which patients indicate the anatomic
location and quality of their symptoms.
Sensitivity and specificity values for the main
signs are, respectively,
•
•
•
•
•
80 and 27% for pain;
97 and 4% for paraesthesiae;
91 and 14% for nocturnal wakening;
51 and 61% for numbness [32];
62 and 52% for simultaneous paraesthesiae
and pain [33].
4.1.2. Physical examination
During a medical examination the right and the
left hands are compared, with special emphasis
on the asymmetry of the muscles in both hands,
in the thenar in particular, and the occurrence of
other pathologies (e.g., ganglions and swellings)
which may compress the nerve. The so-called
trigger points and their tenderness can be detected
by palpation, which tests inflammation in the
structures of the musculoskeletal system.
4.1.3. Clinical manual provocative tests
In diagnoses, in particular in epidemiological
studies of CTS, there are simple provocative
tests typical for the syndrome. These include
Phalen’s manoeuvre (placing the patient’s
wrist in a hyperflexed position for 30 to 60 s
causes pain), Flick test (the patient feels pain
relief by moving the hand as if shaking down a
thermometer), circumduction of the thumb, tests
consisting in actively joining fingertips of finger
I and V (which causes pain sensation), Tinel’s
sign (percussion of the tendon in the wrist region
causes discomfort or pain at the wrist or radiating
distally along the course of the nerve) and
McMurthry’s test (positive if manual pressure
on the palm at the level of the carpal tunnel
precipitates painful symptoms or paraesthesiae).
Provocative clinical tests are easy to conduct
and may be helpful in screening. One should
remember, however, that they contain an
element of subjectivity and for that reason they
should be interpreted with caution, particularly
in the first phase of CTS. Generally speaking,
they are thought to be of little use in diagnostic
examination. Sensitivity and specificity values
for some frequently used tests are presented in
Table 1.
TABLE 1. Sensitivity and Specificity of Manual
Provocative Tests Used in Diagnozing Carpal
Tunnel Syndrome
Tests
Phalen’s
manoeuvre
Tinel’s sign
McMurthry’s test
Sensitivity Specificity
(%)
(%)
Source
71
80
[34]
58
54
[33]
43–86
48–67
[35]
73
36
[36]
42
63
[33]
44
94
[34]
45–63
40–67
[35]
62
66
[36]
49
54
[33]
4.2. Determining Vibration Perception
Threshold
In the practice of an occupational medicine
physician, vibration perception threshold tests are
generally applied in diagnozing the neurovascular
form of the vibration syndrome. They are also
useful in suspected peripheral neuropathies, such
as diabetic polyneuropathy and CTS [29, 37].
Interpretation of those tests requires taking into
account methodological difficulties, including the
influence of disturbing factors, such as ambient
temperature, daily fluctuation of the vibration
perception threshold or the subject’s gender and
age [38]. In peripheral neuropathies, and thus also
in CTS, there is an increased vibration perception
threshold. Compared to nerve conduction velocity
tests (see section 4.3.), vibration perception
threshold tests are noninvasive, well-tolerated
and easy to perform; as such, they are useful in
diagnozing CTS [39, 40, 29, 41]. Sensitivity and
JOSE 2007, Vol. 13, No. 1
34
J. BUGAJSKA ET AL.
specificity vibration perception threshold tests
vary depending on the position of the hand during
the measurements. The best results are obtained
when the wrist is flexed or in an extended
position [41, 42].
4.3. Electrophysiological Examination
Electrophysiological examination based on the
motor and sensory median nerve conduction in
the carpal tunnel is a decisive test verifying a
CTS diagnosis [30, 43, 44]. According to Nathan,
Keniston, Meadows, et al., this test represents
a gold standard in CTS diagnostics [45].
Based on an objective measurement, it detects
sensory and motor neuropathies in the median
nerve, thus confirming the pathomechanism of
CTS symptoms. Although the incidence rate
of subjective ailments typical of CTS in the
professionally active population is high and
exceeds the number of CTS cases confirmed by
objective studies, there are reports of confirmation
by electrophysiological examination of the
features of nerve conductivity damage in persons
who have not reported subjective symptoms [26,
31].
Electrophysiological examination is highly
specific in a clinical setting and reasonably
sensitive. Sensitivity and specificity vary for
different electrodiagnostic techniques that
diagnose CTS. According to a report of the
American Association of Electrodiagnostic
Medicine, the American Academy of Neurology
and the American Academy of Physical Medicine
and Rehabilitation the value of sensitivity is from
62 to 85% and of specificity from 94 to 99%
[46]. According to other sources sensitivity is
from 33 to 74% and specificity from 83 to 100%,
depending on the electrodiagnostic techniques
used [47].
Electroneurography (ENG) is used for
quantitative
assessment
of
parameters
characterizing nerve conduction, such as
conduction velocity, latency times and amplitude
of the signal. These parameters are estimated
on the basis of the measurement of the time
necessary for a nerve impulse to travel the
section between the point of stimulation of the
median nerve and the point of measurement.
JOSE 2007, Vol. 13, No. 1
Compared to healthy individuals, in persons with
CTS the conduction velocity in the median nerve
is reduced, latency times are increased and the
amplitude of the recorded potential is decreased
[48].
Results of electrophysiological examinations
are also used in classification systems of the
CTS sensitivity [49, 50]. All electrophysiological
examinations ought to be performed in
accordance with guidelines for measurement,
temperature, safety precautions and electrode
placement.
4.4. Imaging
Three radiological methods are used in CTS
imaging diagnostics: classic roentgenogram
(RTG), magnetic resonance (MR) and
ultrasonography (USG). RTG only makes
it possible to assess the osseous structures
of the wrist, which may be of importance in
detecting bone anomalies causing median nerve
compression. The assessment of the median nerve
structure as such is possible with MR and USG
imaging [51]. Compared to MR, USG is cheaper
and definitely more accessible; for this reason this
is an increasingly frequent form of imaging in
cases of suspected CTS [52]. Additionally, USG
is so-called real-time imaging, making imaging
of wrist structures possible while patients move
their fingers. That is why it is also a valuable
test used for differentiating tendon and nervous
structures and for confirming inflammation of
tendon sheaths.
In USG testing, in the case of suspected CTS,
thickness and echogenicity of the median nerve,
and the existence of the cause of compression are
evaluated.
The features found in CTS, in USG, and also in
MR include
• decreased thickness of the median nerve in the
carpal tunnel, swelling in the proximal part,
reduced echogenicity and increased palmar
displacement of the flexor retinaculum [53,
54];
• presence of compression causes (e.g.,
inflammation of the flexor tendon sheaths,
radio-carpal joint inflammation and anomalous
CTS IN OCCUPATIONAL MEDICINE PRACTICE
muscle belly of the flexor in the carpal tunnel)
[52].
The most reliable sonographic criterion of
CTS is the cross-sectional area of the median
nerve at the entrance to the carpal tunnel (i.e.,
at the level of the pisiforme bone). According to
different authors, it ranges from 0.07 to 0.20 cm2,
depending on the calculating methods used
(Table 2). Similar values are used in MR.
TABLE 2. Sensitivity and Specificity of
Ultrasonography Measurements Used in Carpal
Tunnel Syndrome (CTS) Diagnosis for Different
Values of Cross-Sectional Areas of the Median
Nerve Suggested as a Criterion for CTS
Cross-Sectional
Areas of the
Median Nerve Sensitivity Specificity
(mm2)
(%)
(%)
Sources
>9
82.8
97.1
[53]
11
89.1
98.0
[55]
11
73.4
57.1
[56]
9.3
92.0
98.0
[52]
5. PREVENTIVE MANAGEMENT
Despite
technological
progress,
there
are still many types of work that involve
high repetitiveness of working actions or
uncomfortable, forced postures of hands in
particular. In the practice of an occupational
medicine physician taking care of groups of
workers who are exposed to such factors, the
fundamental problem, besides exposure to risk
factors, is early identification of persons with
CTS. Preventive procedures based only on
periodic assessment of subjective ailments seem
to be unsatisfactory. According to Wainner,
Fritz, Irrgang, et al. the development of a Clinical
Prediction Rule for diagnozing CTS is mandatory
[57]. A Clinical Prediction Rule is defined as
“a tool used by clinicians to assist with medical
decision making that provides either a probability
of disease or outcome or suggest a diagnostic or
therapeutic course of action” (p. 490) [58].
Fallentin defines the area of work-related
MSDs as a grey zone, in which there is a
deficiency of tests to enable actual determination
of the incidence rate of this phenomenon and
35
specification of the dose–response relationship,
and thus to assess risk at such workplaces [59].
An exhaustive review of epidemiological tests in
this regard carried out by the National Institute
for Occupational Safety and Health (NIOSH) and
National Research Council (NRC) in the USA
has revealed lack of studies in this area [18]. The
studies carried out thus far have demonstrated
that the relationship between the incidence of
certain professional factors and the occurrence
of MSDs is unambiguous, yet no critical point of
exposure to these factors has been identified to
date. This issue requires more clinical studies.
6. SUMMARY
CTS is one of the best known overload syndromes
associated with the type of work. Although
factors and pathophysiological mechanisms of
CTS are very well understood now, the problem
of early diagnosis of this syndrome remains
open. Occupational medicine has a battery of
clinical and physiological tests which are applied
to confirm a diagnosis of CTS. In OSH practice
the main goal should be to prevent the onset of a
problem or to identify it as soon as possible. To
achieve this goal, in addition to the careful and
systematic ergonomic analysis of a workplace
done by an OSH specialist, periodic examinations
of workers exposed to the risk factors of CTS
done by occupational medicine physicians seem
to be the most appropriate approach.
During those examinations, it is very important
for the physicians to be able to conduct simple
tests for sensory neuropathy of the median
nerve, e.g., tests for the threshold of vibratory
sensibility, in addition to interviews and clinical
provocative tests. This would make it possible—
because of the frequent subjective symptoms in
the population of workers involved in manual
work—to be more precise in identifying people
who might have CTS and to refer them quicker
to specialist and more expensive diagnostic tests
(e.g., ENG and imaging examination).
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J. BUGAJSKA ET AL.
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