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 ^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
Downloaded from http://occmed.oxfordjournals.org/ at Pennsylvania State University on March 4, 2014
R. Larsson,* H. Cai,* Q. Zhang,1 P. A. Oberg* and S. E. Larsson*
190 Occup. Med. Vol. 48, 1998
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
Downloaded from http://occmed.oxfordjournals.org/ at Pennsylvania State University on March 4, 2014
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.
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
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
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.
Downloaded from http://occmed.oxfordjournals.org/ at Pennsylvania State University on March 4, 2014
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
191
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»
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
Downloaded from http://occmed.oxfordjournals.org/ at Pennsylvania State University on March 4, 2014
rms-EMG 2 kg
rms-EMG 2 kg
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
30
60
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
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
Downloaded from http://occmed.oxfordjournals.org/ at Pennsylvania State University on March 4, 2014
0
| painful side a opposite side
193
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.
1. Larsson S-E, Bodegard L, Henriksson KG, Oberg PA. Chronic trapezius myalgia. Morphology and blood flow studied in 17 patients. Acta Orthop Scand 1990; 61: 394-398.
Downloaded from http://occmed.oxfordjournals.org/ at Pennsylvania State University on March 4, 2014
REFERENCES
2. Salerud EG, Oberg PA. Single fiber laser-Doppler flowmetry. A method for deep tissue perfusion measurements. Med Biol Eng Comput 1987; 25: 329-334.^ 3. Larsson S-E, Cai H, Oberg PA. Continuous percutaneous measurement by laser-Dopper flowmetry of skeletal muscle microcirculation at varying levels of contraction force determined electromyographically. Eur J Appl Physiol 1993; 66: 477-482. 4. Larsson S-E, Cai H, Oberg PA. Microcirculation in the upper trapezius muscle during varying levels of static contraction, fatigue and recovery in healthy women. A study using percutaneous laser-Doppler flowmetry and surface electromyography. Eur J Appl Physiol 1993; 66: 483^88. 5. Larsson S-E, Alund M, Cai H, Oberg PA. Chronic pain after soft-tissue injury of the cervical spine: trapezius muscle blood flow and electromyography at static loads and fatigue. Pain 1994; 57: 173-180. 6. Basmajian JV, DeLuca CV. Muscles Alive. Their Functions Revealed by Electromyography. Baltimore, MD (USA): Williams andWilkins, 1985. 7. Jarvholm U, Palmerud G, Karlsson D, Herberts P, Kadefors, R. Intramuscular pressure and electromyography in four shoulder muscles. J Orthop Res 1991; 9: 609-619. 8. Cornefjord M, Olmarker K, Farley DB, Weinstein JN, Rydevik B. Neuropeptide changes in compressed spinal nerve roots. Spine 1995; 20: 670-673.
