Occup. Med. Vol. 48, No. 3, pp. 189-194, 1998
Copyright© 1998 Rapid Science Ltd for SOM
Printed in Great Britain. All rights reserved
0962-7480/98
Visualization of chronic
neck-shoulder pain: Impaired
microcirculation in the upper
trapezius muscle in chronic
cervico-brachial pain
R. Larsson,* H. Cai,* Q. Zhang,1 P. A. Oberg* and
S. E. Larsson*
^Department of Orthopaedics, University Hospital, S-501 85 Linkping,
Sweden; ^Department of Biomedical Engineering, University Hospital,
S-501 85 Linkoping, Sweden
This study pertains to the 71 patients who had received a diagnosis of cervico-brachial
pain syndrome after thorough clinical examination of a total series of 300 patients,
who had been referred to the National Insurance Hospital in Tranas because of
chronic neck pain that interfered with their ability to work. Changes in trapezius
muscle blood flow and EMG were examined and related to the anamnesis and
physical findings. The microcirculation in the upper part of the right and left
trapezius muscles was examined simultaneously by using optical laser-Doppler
single-fibres after insertion into the muscle directly via the skin. Continuous
recordings were made during stepwise increased static contraction determined
electro-myographically. Signal processing was performed on-line by computer.
MRT of the cervical spine was performed in 12 patients. None showed nerve root
affliction. Ten showed a bulging intervertebral disc and two, a narrowed nerve hole
(lateral stenosis). The muscle blood flow (LDF) was significantly lower in the most
painful side compared with the opposite side in the group of 41 patients with
predominantly unilateral pain (21 women and 20 men). A lowered blood flow was
also found when the 21 females in this group was compared with a normal control
group of 20 healthy women. The patients had lower rms-EMG and EMG mean power
frequency (MPF) in the painful side compared with the opposite side. A further
lowering of the MPF was observed with induced fatigue. It was concluded that the
chronic neck pain in cervico-brachial syndrome can become visualized by the
finding of lowered blood flow of the trapezius muscle which seems to be an
expression of the chronic neck pain.
Key words: Chronic neck pain; electromyography; Laser Doppler flowmetry; mean power
frequency; microcirculation.
Occup. Med. Vol. 48, 189-194, 1998
Received 2 July 1996; accepted in final form 30 October 1997.
INTRODUCTION
Chronic neck pain of different causes is a common
reason for work absenteeism. Previously, we studied
muscle changes in women who were doing highly
repetitive assembly work for several years. The majority
of the women had painful, tense trapezius muscles as
well as local pain and fatigue, as in trapezius myalgia.
Correspondence and reprint requests to: R. Larsson, Department of
Orthopaedics, University Hospital, S-501 85 Linkoping, Sweden.
Isolated muscle fibres with morphologic signs of
mitochondrial disturbance were found and lowered
levels of energy-rich adenosine triphosphate and
adenosine diphosphate, probably caused by impaired
synthesis.1 We were then able to show, in a combined
muscle biopsy and circulatory study, a lowered muscle
blood flow which correlated with discrete signs of
mitochondrial disturbance in the slow, type I muscle
fibres ('ragged red fibres') and local pain.1 In that
study, we measured the blood flow with a relatively
large laser-Doppler probe that was applied to the
190 Occup. Med. Vol. 48, 1998
surface of the surgically exposed muscle fibres.
We have now performed continuous measurements
of the microcirculation in the right and left trapezius
muscles by adopting a percutaneous single-fibre
technique2 for dynamic measurements directly via the
skin/"5 Periods of stepwise increased static contraction
and rest were determined electromyographically
(EMG), and the blood flow in the upper trapezius
muscle was related to the activity of the muscle.
Using this atraumatic technique in previous studies,
we could demonstrate a disturbed regulation of the
microcirculation in the trapezius muscle in patients
with chronic neck pain related to a previous car accident soft-tissue ('whiplash') injury of the cervical
spine.5 This disturbance seemed to be an expression
of the chronic neck pain. Many of the patients were
found to develop chronic trapezius myalgia which
might maintain the 'whiplash-pain'. Possibly, it may
also play a role in chronic cervico-brachial pain syndrome. Chronic cervico-brachial pain is common in
society. It is often related to strenuous work in the
middle-age worker who has degenerative changes of
the cervical spine. Most patients complain of diffuse
neck pain, sometimes irradiating towards the shoulder
and arm. Neurological symptoms are rare in contrast
to cervical rhizopathy which is caused by nerve root
compression. There is little nerve root irritation, and
the diagnosis is often based upon subjective symptoms.
Many patients describe pain in the trapezius region
of the neck-shoulder.
We are reporting on bilateral recordings of the
microcirculation and EMG in the upper portion of
the right and left trapezius muscle during varying
levels of static contraction with development of fatigue.
A series of 71 patients was examined, all with
long-lasting work absenteeism due to chronic cervicobrachial pain of the neck. Clinical signs of abnormality
were few and none had evident cervical rhizopathy.
MATERIALS AND METHODS
Controls
Twenty healthy female subjects gave informed consent
to participate as normal controls. They had no complaints and took no medication that could interfere
with the results of the study. All of them had jobs with
ordinary, variable tasks within the hospital, none causing monotonous load to the shoulders. Mean age was
44 years (25-63 years). Their body height was 163
centimetres (153-176 centimetres) and body weight
was 66 kg (47-85 kg). All were natives of Sweden.
Twelve were moderate smokers.
Patients
These consisted of the 71 cases (23.7%) who had
received a diagnosis of cervico-brachial pain syndrome
among our total examined series of 300 patients with
chronic neck pain who had been remitted to RFV
Hospital in Tranas, Sweden, for thorough in-patient
medical examination because of long-lasting pain and
work inability. The purpose was to derive more objective medical information upon which to base work
rehabilitation. The hospital stay and the medical examinations and treatments were paid for by the official
insurance (Riksforsakringsverket). The patient
received financial compensation from the official
insurance during his stay at the hospital. Informed
agreement to participate in the study was given by all
patients. Consent to the study was given by the
Research Ethics Committee at our hospital.
Exposure to static load
The right and left trapezius muscles were simultaneously exposed to stepwise increased static load for
periods of 1 min each with 1 min of rest in between.
The patient was sitting upright in a standard office
chair with relaxed, hanging arms (rest position). On
command, the patient raised straight arms symmetrically in the scapular plane (approximately midway
between abduction and flexion) to subsequently 30°,
60°, 90° and 135°, i.e., the load positions. This was
then repeated with a 1 kg (women) or 2 kg (men)
load carried in each hand. Finally, a fatigue test was
performed with straight arms elevated at 45° holding
a 1 kg (women) or 2 kg (men) load in each hand.
Recovery was then achieved with hanging arms and
no hand load. LDF and EMG signals were recorded
continuously during the three 10 min tests.
EMG
EMG was recorded simultaneously with LDF by using
bipolar surface electrodes (Medicotest pre-gelled child
ECG-electrodes), placed over the right and left
trapezius muscle halfway between the spinous process
of the C7 vertebra and the acromion. The centre-tocentre inter-electrode distance was 2.0 cm. The
reference electrode was placed over the spinous process of C7. EMG signals were visualized on an
oscilloscope for testing electrode function.
Laser-Doppler Flowmetry (LDF)
LDF was used for simultaneous measurements of the
microcirculation in the upper portion of the right and
left trapezius muscles, as we have described in detail
previously.3 The optical single fibres used2 had a
diameter of 0.5 mm and were placed percutaneously
within the muscle halfway between the spinous process
of the C7 vertebra and the acromion. Insertion was
made via a plastic cannula (Venflon 2 i.v. cannula, 1.0
mm outer diameter, Viggo, Helsingborg, Sweden) that
had been inserted into the muscle to lead the optical
fibre to the maximal depth for the recordings, i.e. 5-10
mm from the point where the subject noticed the
R. Larsson et a/.: Visualization of chronic neck-shoulder pain
somewhat painful passage of the cannula through the
muscle fascia. A laser-Doppler flowmeter (modified
Periflux, Pfld Perimed, Stockholm, Sweden) was used
for the measurements (time constant 0.2 sec; 4 kHz;
gain 1). All determinations were performed in a quiet
laboratory room and at a temperature of 20-22°C.
Signal processing
The experimental set-up was similar to that used in
our previous study.5 LDF and EMG signals were
converted into digital form in an A/D converter
(AT.MIO-16, National Instruments, USA) with a resolution of 12 bits and processed on-line by computer
(Intel 485/66 MHz processor). Fast Fourier transform
was performed using Lab-Windows program. Root
mean squared EMG (rms-EMG) as well as mean
power frequency (MPF) were calculated by using 0.5
sec segments. For each 1 min examination period we
used 20 segments representing the 40-50 second part
with exclusion of the first and the last segments to
avoid disturbances from sample processing. A total of
18,432 points were used per measurement. LDF was
calculated for each consecutive 1 min examination
period by using the last 20 sec of each period. Before
filtering, 2,048 points/sec were used.
Processing in a digital Butterworth low-pass filter of
8th order was used for a frequency range of 0-8.2 Hz
which corresponded to the blood flow spectrum of
interest. MPF was calculated mainly according to
Basmaijian and DeLuca.6
Statistical analyses
Regression analyses were performed according to
Neter et aV Paired r-tests were used according to
Snedecor and Cochran8 when the two shoulders of
each patient were compared, and also for comparison
of the different means within the series. Unpaired
r-tests were used when the female patient group was
compared with the control group, p < 0.05 was
considered significant.
RESULTS
191
Forty-one of the 71 patients had predominantly
unilateral pain (20 men and 21 women), and the rest
had bilateral pain. The most painful side of the 41
patients was compared with the opposite side. In
addition, the most painful side in the 21 female patients
was compared with the average of the two sides in the
healthy controls.
Thirteen patients were unemployed. Twenty-one
patients had long-term work-absenteeism due to constant complaints of neck pain. All received economic
compensation from the official insurance. Two patients
had their daily sickness compensation transformed into
pension for a limited period of time. Fifteen patients
also received compensation from the official work
insurance because their complaints were related to
work factors. An additional 22 claimed that their complaints were caused by work factors.
Workload
Thirty-one patients (44%) had jobs including heavy
lifting. Five (7%) were doing sitting monotonous
assembly work with light details and another five in
machinery. As many as 41 (58%) had standing jobs
that necessitated frequent elevation of the arms. Seventeen (24%) were exposed to vibrations and repeated
rocking forces to their arm-shoulder. As many as 26
(37%) were nursing personnel.
Physical examination
Eighteen patients had slight sensory disturbance of
the arm-hand, and 11 suspected arm reflex impairment. Cervical rhizopathy of a minor degree was
suspected in 27 patients (38%), but among them were
six who had complaints only temporarily after heavy
work load. Four patients had trigger points eliciting
pain of neuralgic character. A clinical diagnosis of
chronic trapezius myalgia had been made in 19 of the
71 patients (27%). Thirty patients had reduced motion
range of the neck and nine of the shoulder(s). One
patient had impingement syndrome of the shoulder.
Twenty-six reported complaints of lumbago-ischias.
None had clinical evidence of thoracic outlet
syndrome.
Obtained patient data
Using a form with 250 items, information was collected
as regarded previous anamnesis, psycho-social data,
work, physical findings and medical laboratory examinations:
There were in total 71 patients (34 men and 37
women). The mean age was 44.5 years. Sixty-three
were native Swedish and eight (11%) came from other
countries. Active working years were on average 21.
Periodic neck-shoulder complaints started at a mean
age of 36.5 years. None of the subjects were workactive at the time of the examination, and the present
sickness period was 26 months on average.
Roentgenographical examination
This was undertaken in 51 patients. It showed no
abnormality in 21; spondylosis in seven, spondylarthrosis in six and disc degeneration in 17. There
were no signs of instability or subluxation. There was
no evidence of previous fracture.
Magnetic resonance tomography of the cervical spine
was made in 12 cases. None had evidence of nerve
root affliction. 'Bulging' disc that caused no nerve root
compression was found in 12 patients; causing stenosis
of the spinal canal in 10, and stenosis of intervertebral
nerve hole in two cases.
192 Occup. Med. Vol. 48, 1998
Figure 1. Continuous recordings of LDF and rms-EMG during alternating 1 min periods of rest and stepwise increased static contraction at varying degrees of arm elevation and repeated with a 2 kg hand load. Motion artefacts in LDF are seen during elevation
and lowering of the arms at the beginning and the end of each examination period. LDF was therefore measured during the last
20 s of each 1 min period. The LDF and rms-EMG are lower on the painful left side compared with the opposite side.
Painful side
fjinmti
Opposite side
rms-EMG 0 kg
rms-EMG 0 kg
LDF Okg
LDF 0 kg
i flfc m |M»
rms-EMG 2 kg
rms-EMG 2 kg
LDF 2 kg
ji
6
7
8
9
10
8
LDF and EMG signals
The LDF and EMG recordings from one of our subjects are shown in Figure 1. The LDF was lower in
the painful, left side compared with the opposite side.
The rms-EMG showed low amplitudes in the left side,
probably due to pain inhibition.
10
Figure 2. The rms-EMG, MPF and LDF of the most painful
side (black columns) and the opposite side (grey columns) in
41 patients with cervicobrachial pain. Paired Mest for means
showed significantly lower values in the painful side compared
with the opposite side for rms-EMG and muscle blood flow
(LDF). Values obtained at 0°, 60° and 90° angles of elevation
and no hand load showed a significantly lower LDF in the
most painful side, and also at 60° and 90° with a hand load
of 1 kg for women or 2 kg for men (stars).
Patients with unilateral pain
The results obtained in the most painful side were
compared with those of the opposite side in the group
of 41 patients (21 women and 20 men) who had
predominantly unilateral pain (Figure 2). Paired t-test
for the obtained group means showed significantly
lower values (j> < 0.0001) for rms-EMG in the painful
side compared with the opposite side. The differences
were consistent at the different contraction intensities.
The group means for the EMG-spectrum (MPF)
showed significandy higher values in the painful side
than in the opposite side at low contraction intensities
with no hand load, but no difference at high contraction intensities with hand load.
The muscle blood flow in the group of patients
shown in Figure 2 was consistently lower in the most
painful side than in the less painful side (p = 0.0144).
In addition, the 21 female patients with predominandy
unilateral pain had significantly lower blood flow in
the most painful side (Figure 3) than the normal
control group of healthy women (p = 0.0009). The
9
Minutes
Minutes
Okg
3l>
«>
I patient group
I control group
90
133
Angle
y>
«)
90
133
R. Larsson et al.: Visualization of chronic neck-shoulder pain
Figure 3. The same parameters as in Figure 2 for the 21 female
pain patients compared with a control group of 20 healthy
women. The series of values obtained for the rms-EMG, MPF
and muscle blood flow (LDF) when tested without and with
hand load were all significantly lower in the patient group
compared with the control group (except for the 135° elevation with hand load).
unload
load
rms-EMG
0
30
60
| painful side
a opposite side
90
135
0
30
60
90
135
Angle
rms-EMG in the patients showed significantly lower
(p < 0.0001) amplitude in the painful side than in the
opposite side, especially at higher contraction levels
and probably due to central pain inhibition. The E M G spectrum (MPF) was slightly lower in the painful side
than in the opposite side of the patient group. T h e
difference was statistically significant only when the
series of contraction values for the whole groups were
tested together (Figure 3).
DISCUSSION
The results of the present study indicate that there
exists a correlation between chronic neck pain in
patients with cervico-brachial syndrome and impaired
microcirculation of the trapezius muscle. T h e expression of pain by a lowered blood flow of the trapezius
muscle was also found in patients with chronic neck
pain due to work-related chronic trapezius myalgia 1
and in patients with chronic neck pain persisting after
a previous car accident whiplash trauma. 5 This seems
to be a physiologic expression of chronic neck pain
and may be useful in the clinical evaluation of these
patients. Together with the E M G examination, determ i n a t i o n of m u s c l e blood flow may also give
information about whether the pain is neurogenic or
nociceptive (Larsson et al., to be published). The lowered blood flow in nociceptive muscle pain is associated
with an increased muscle tension as determined by the
193
rms-EMG. T h e blood flow is also lowered in neurogenic pain but there is a characteristic central inhibition
of the muscle tension. This information is clinically
important because treatment is different.
Bias may be caused by differences in intramuscular
pressure that influence the muscle blood flow, and
technical faults. The trapezius muscle has a relatively
low intramuscular pressure, seldom exceeding 50 mm
Hg at varying angles of arm elevation. 7 We found a
lowered trapezius blood flow also in neurogenic pain
where the muscle tension showed central inhibition
(Larsson et al, to be published). Before use we calibrated our laser-Doppler equipment by using a rotating
disc. T h e same flowmeter and optical fibre were used
consistently in the same side of the patients throughout
the series and we used simultaneous measurements in
the right and left muscles. T h u s , the pain side was an
independent variable appearing by chance.
Of our 71 patients there were 41 with predominantly
unilateral pain; 20 in the right side and 21 in the left
side. This group of 41 patients showed significantly
lower muscle blood flow in the painful side than in
the opposite side. In addition, the female patients had
a lower muscle blood flow in comparison with healthy
females who served as a normal control group.
T h e E M G showed lower muscle tension in the painful side than in the opposite side of the patients during
bilateral stepwise increased static shoulder load. T h e
inhibited muscle tension certainly resulted in reduced
intramuscular pressure. Nevertheless, a lowered
muscle blood flow was recorded.
The described impaired microcirculation might be
related to factors which are normally involved in the
regulation of chronic pain. Neuropeptides act not only
as transmitters of nerve signals but are also potent
microcirculatory stimulators, such as substance P
which is released from the peripheral nerve terminals.
Recently, it has been shown in pigs that there is an
increase of substance P concentrations in experimentally constricted dorsal nerve roots just cranially to a
constricted part of the nerve root in comparison to
the noncompressed side. 8 Compression might cause a
hindrance to peripheral secretion of neuropeptides.
Therefore, one would speculate a peripheral, regional
deficiency of neuropeptides in chronic pain caused by
nerve compression. A reduced peripheral content of
neuropeptides might explain the impaired microcirculation of the trapezius muscle in patients with chronic
neck pain.
The MPF, one of the E M G signs of muscle fatigue,
was analyzed in the whole group of 41 patients with
unilateral pain (21 women and 20 men) by comparison
of the painful side and the opposite side. N o statistically
significant differences were found when the painful
side was compared with the other side. This difference
was evident also when the whole group of female
patients with predominantly unilateral pain was compared with the healthy control women.
In conclusion, evidence was obtained that chronic
neck pain as in cervico-brachial syndrome is associated
194
Occup. Med. Vol. 48, 1998
with a lowered intramuscular blood flow in the upper
part of the trapezius muscle. Together with rms-EMG
which showed some inhibition of muscle tension this
may indicate that this kind of neck pain is of predominantly neuralgic type caused by nerve root irritation
due to degenerative changes of the cervical spine.
Although this examination cannot give information as
to the exact level of origin of the chronic neck pain,
it may be used to visualize this type of chronic neck
pain which is of value in the clinical evaluation of
these conditions.
ACKNOWLEDGEMENTS
This study was supported by the Swedish Work
Environment Fund; project no. 96-0990.
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