Reduced postural control in patients with chronic cervicobrachial pain syndrome

Reduced postural control in patients with chronic cervicobrachial pain syndrome M Karlberg Departments Sweden

MD’, L Persson

PT BSc*, M Magnussonl

of lOto-rhino-laryngology

and *Neurosurgery,

University

MD Ph D Hospital,

Lund,

Summary Dizziness and subjective balance disturbances are frequent complaints in cervical pain syndromes of different origins. We objectively assessed balance function with posturography using vibration-induced and galvanically induced body sway in consecutive patients with cervicobrachial pain syndrome of more than 3 months duration. Both a group of patients with MRI-verified cervical root compression (CRC group, n = 891, and a group with normal MRI of the cervical region (non CRC group, n = 18) manifested significantly poorer postural control than sex- and age-matched controls (n = 20). Disorders of the neck should be considered when assessing patients complaining of dizziness or vertigo. Key words: Posturography, Gait & Posture

posture, neck pain, disc hernia, cervical spondylosis

1995; Vol. 3: 241-249, December

Introduction Dizziness, non-rotatory vertigo and a feeling of unsteadiness are frequent complaints in patients with headache of cervical origin, cervical spondylosis and after cervical soft-tissue traumai4. Few studies, however have objectively assessedpostural competence in subjects with neck complaints, and the importance of cervical aetiologies in balance disorders has been challengeds. Vestibular afferent input provides central nervous structures with information about head position and head movement in space, but not about head position and movement in relation to the trunk which, it has been suggested, is provided by cervical proprioceptive input instead637.Animal experiments have shown that afferent neck information and labyrinth information ‘travel together’, and converge at several locations in the CNS, such as the vestibular nucle+lo. In recordings made during head movements from single neurons in the vestibular nuclei receiving afferents both from the labyrinth and from the cervical proprioceptors, the Received: 25 January 1994 Accepted: 14 February 1995 Correspondence and reprint requests to: Mikael laboratory. Department of Otolaryngology, S-221 85 Lund, Sweden 0966-6362/1995

$9.50 0 Elsevier

Science

B.V. All

Karlberg, University

rights

Vestibular Hospital,

reserved

signals from the two sources are out of phase and tend to cancel each other out”. Thus, whole body movements elicit responses differing from those elicited by isolated head movements such as nodding or shaking the head. Cervical proprioceptive input affects eye movements (the cervico-ocular reflex) and posture (the tonic neck reflex) both in animals and in man, but in man the effect on posture can only be observed during the first months of life or after severe brain damage’?. Sectioning of the dorsal cervical roots produces ataxia in animalsi3, and infiltration of local anaesthetics into the deep tissuesof the neck produces ataxia in both humans and animals, but nystagmus in animals only]“. Hence it is reasonable to assume that disturbed cervical proprioception primarily will affect postural control in mans. Patients with neck pain have a poorer ability to reassume the original position of the head after an active head movement, indicating an alteration in neck proprioceptionis; and restriction of cervical mobility by a cervical collar impairs both postural control and voluntary eye movements in healthy subjectsi6. Thus it appears that cervical sensory input can be impaired in patients with neck pain, and may be accompanied by disturbances in postural control. Preferably, the assessmentof postural control function should be based on objective measurements. Henriksson and colleagues used a posturographic tech-

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nique to record body sway in vestibular lesion patients during the Romberg testi7, though the procedure was found to have limited clinical applicationls. To enhance the value of posturography in assessing balance disorders, the measurements of postural control function can be made during or after a postural perturbationig. Alternatively, postural perturbation may be induced by the application of erroneous sensory input, such as exposing the proprioceptive receptors to a vibratory stimulus20, the vestibular nerves to a galvanic stimulus2i, or vision to sway-referenced condition with the EquitestTM 22. Application of a vibratory stimulus on the antigravity muscles causes proprioceptive ‘misinformation’, producing a sensation of movement, and consequently a shift in body posture2Q4. Vibration of the calf muscles induces retrograde body deviation, whereas vibration of the neck muscles causes anterograde deviatio+. Both stimuli increase body sway; and increasing the frequency of the vibratory stimulus up to about 80-100 Hz induces corresponding increases in body sway velocity26. Healthy subjects and patients with compensated peripheral vestibular disorders react more to calf muscle vibration than to neck muscle vibration, whereas patients with CNS disorders such as brainstem infarction or spinocerebellar degeneration are more sensitive to neck muscle vibration26. Application of bipolar electric stimulation to the head near the ears induces lateral body deviation towards the side with the positive electrode (galvanically induced it body sway)27, and at higher stimulus intensities induces reflexive eye movements (galvanic nystagmus)*s. These reactions are considered to be related to vestibular nerve function, and to be independent of vestibular end organ functionZ9. The direction of galvanically induced body sway is dependent on horizontal head position in relation to the trunk, showing that mechanoreceptors in the neck inform equilibrium control centers in the CNS about head postition7. Galvanically induced body sway has been proposed as a direct vestibular stimulus suitable for use in postural testingz7. No studies of postural competence have been with cervicobrachial pain performed in patients syndrome only, but some studies have been made in patients with vertigo of suspected cervical origin. In posturographic tests on a stable platform with the subject’s head extended, both de Jong and Blesi and Nor& et al.30 found body sway to be increased in some patients with vertigo of suspected cervical origin. However, this is also found in patients with M&i&e’s disease or benign paroxysmal positional vertigojo, as well as in normal subjects31. Using the EquiTest TM to study postural competence in patients with common neck disorders and concomitant vertigo, as compared to healthy subjects, Alund and colleagues found postural stability to be impaired in the patients when tested with the head in the neutral position, in left rotation and in right lateral flexion, and in the head position reported by the patient to be most prone to elicit vertigo, but not

with the head extended or in any other of seven different head positions32. Vitte and co-workers, who used the EquiTest TM to study 34 patients with complaints of dizziness and unsteadiness and concomitant cervicobrachial neuralgia, found performance to be poorer in test conditions utilizing vestibular information only, and latency in postural responses to be longer after movement of the supporting surface. MRT scans revealed narrowing of the cervical canal and discopathy with posterior herniation into the vertebral canal in many of their patient+. The aim of the present study was to ascertain whether, as compared to healthy subjects, patients with chronic cervicobrachial pain syndrome have disturbed postural control, as objectively analysed by posturography using vibratory induced body sway and galvanically induced body sway20,“,34. Methods

Putients und controls The series comprised 121 consecutive patients with neck pain and radiating arm pain of more than 3 months duration, referred to the Department of Neurosurgery, University Hospital, Lund, for evaluation of possible surgical treatment. Patients with whip-lash or other traumatic injuries were not included. All patients were examined by the same neurosurgeon and the same physiotherapist (LP). Plain X-rays and magnetic resonance imaging (MRI) (n = 110) of the cervical column or cervical myelography (n = 11) were performed. The patients answered a questionnaire including duration of cervicobrachial pain, past medical history and complaints of dizziness, vertigo, or balance disturbances. Intensity of present cervicobrachial pain was measured on a horizontal lOOmm visual analogue scale (VAS) ranging from ‘no pain’ at one end to ‘extreme pain’ at the other. The active range of cervical motion was measured with a Myrin goniometer, and expressed as the aggregate of values for extension/flexion and axial rotation. Vestibular function was assessed at clinical investigation to exclude the presence of spontaneous, gaze or positional nystagmus in Frenzel glasses including the headshake test35. Pure tone audiometry was performed if the patient had any hearing complaints. Of the 121 referrals, three patients were excluded from the study because of unilateral deafness (and thus possible concomitant vestibular disorders), one patient because of previous arthrodesis of the ankle (interfering with posturographic testing), and one patient because of lack of co-operation at posturographic testing. Nine patients manifested symptoms and radiological signs suggestive of medullary compression and were excluded. Of the remaining 107 patients, 89 manifested symptoms and radiological signs suggesting cervical root compression only (the CRC group), and 18 patients manifested no signs (or only negligible signs) of pathology at neuroradiological examination of the cervical column (the non CRC group). The postural control test data of

Karlberg

et al.: Postural

the CRC group and the non CRC group were compared separately with those of the controls. Twenty healthy subjects were recruited from the hospital staff as a sex- and age-matched control group. None of these subjects had any history of vertigo, balance disturbance, ear disease, central nervous system disease, neck pain, cervical spine disease or major injury affecting the lower limbs. The characteristics of the CRC group, the non CRC group and the control group are given in Table 1. The use of alcoholic beverages or sedatives was proscribed for 24 h preceding the posturographic tests. The patients were allowed to take analgetics of NSAID type if needed. Tests of’postural

control

Postural control was evaluated by recording the forces actuated by the feet on a custom-built force platform (400 X 400 X 75 mm) equipped with strain gauge@. During recordings the subjects stood upright with the knees extended, arms crossed over the chest and with the heels together but not touching, the feet forming an angle of 30 degrees. The subjects stood either with the eyes closed or focused on a mark on the wall at a distance of 1.5 m. To eliminate auditory clues as to position, the subjects were provided with headphones relaying music (Haffner Serenade, W.A. Mozart, KV 250). The movements of the centerpoint of pressure actuated by the feet were recorded with the force platform. The signal from the platform was filtered by a 25Hz analogue low-pass filter and sampled by a computer (Compaq 386/20) at 33 Hz (recordings for velocity of vibration-induced body sway) or at 10 Hz (recordings for identification of postural dynamics and variance of vibration-induced body sway and galvanically induced body sway). Signal analysis was performed with a mathematical software package (386-Matlab, Mathlab Inc. USA). Table

1. Characteristics

of the groups

Characteristics Men Women Age (years) Height (cm) Weight (kg) Pain duration (months) VAS pain intensity Cervical range of motion (degrees) Vertigo/dizziness (%I Unsteadiness (%) Vertigo/dizziness or unsteadiness (%I Values are means k SD. n.s. = P> 0.05, ** = PC 0.01

control

with cervicobrachial

pain syndrome

243

Vibrurion-induced body sway

Velocity of body sway, identification of characteristic parameters of postural dynamics, and variance of body sway The subject’s posture was perturbed mainly in the anteroposterior plane by a vibratory stimulus applied to the calf muscles causing retrograde body deviation, or to the paraspinal neck muscles causing anterograde body deviation. The vibrations were generated by a revolving DC motor (Escap, Switzerland) equipped with a 3.5 g unbalanced weight at one end. The vibrator was built into a metal cylinder, length 50 mm and diameter 18 mm. The frequency of vibration was controlled by varying the input voltage of the DC-motor. The vibrators were attached to the belly of the gastrocnemius muscle on both legs with elastic straps, and to the paraspinal neck muscles above the seventh vertebra with a neck collar (Philadelphia model 62, Camp Ltd., Portsmouth, GB), avoiding contact with the cervical column itself. In tests assessing body sway velocity, the vibratory stimulus was applied at a peak to peak amplitude of 0.4 mm for periods of 10 s at five different frequencies (20, 40, 60, 80 and 100 Hz) in a pseudorandomized order controlled by the computer. Velocity of body-sway in the anteroposterior plane was calculated separately for the different periods of vibration and for a preceding 10 s. stimulation-free period of quiet stance36. In order to use system identification of a third-order Armax model of an inverted pendulum previously validated as a model of the control of upright human stance34, the subjects were exposed to vibration at a fixed frequency of 60 Hz and an amplitude of 0.4 mm. The stimulus was given according to a pseudorandom binary sequence (PRBS) schedule with pulses between 0.5 s and 8 s length for 205 s, preceded by a stimulationfree period of 30 s. The three normalized parameters of the transfer function (i.e. stqjhess, swijhzess and damping) describe the dynamics of postural control in the anteroposterior plane corresponding to a PID

studied Healthy subjects

Cervical root compression (n = 89)

No cervical compression

50 39 47 2 171+9 76 2 34* 42 2

13 30 24

n.s. n.s. n.s. n.s. **

11 7 49 ” 7 174 29 75* 15 30 2 25 59 2 24

-

202 + 48 46 (52) 31 (35)

** n.s. n.s.

180258 9 (50) 8 (44)

-

54 (61)

n.s.

11 (61)

12 8 45 f 9 177211 752 12 -

(n = 20)

n.s. n.s. ns.

8

root (n = 18)

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Gait & Posture

1995; 3: No 4

controller (i.e. proportional, integrative and derivative control). Stz@eless describes the reaction of the body on proportional deviation from the assumed resting position, and swifiness (corresponding to integrative control) defines the time required for realignment to the initial resting position after a perturbation. Dumping describes the control action dependent on the velocity of the body-sway induced by a perturbation37. These recordings were also analysed for variance of body sway in the anteroposterior plane. The variance of body sway is proportional to the mechanical energy in the sway, and was used to assesspostural control’r. All subjects underwent tests both with vibratory stimulation applied to the neck and to the calf muscles, and under both open eyes and closed eyes conditions.

data for the healthy control group were normally distributed (Figure 1). Consequently, the non-parametric Mann-Whitney test was used to compare the posturographic data of the two patient groups with each other, and with those of the control group. As values for clinical data were normally distributed in both of the patient groups, an unpaired two-tailed t test was used for comparison. Correlations between VAS pain intensity ratings, duration of symptoms, cervical active range of movement, and posturographic test results was calculated. P values co.05 were considered statistically significant. Results Clinical dutu und churucteristics

Gulvunicully induced body sway Variance of body sway Body posture was perturbed mainly in the lateral plane by means of bipolar binaural galvanic stimulation of the vestibular nerves. Two 3.5 X 4.5 cm carbon-rubber electrodes (Cefar AB, Lund, Sweden) were placed one on each mastoid. A custom-built constant current generator delivered a galvanic stimulus to the electrodes at a peak to peak amplitude of 1.O mA. The electrode polarity was shifted according to a computer-controlled PRBS schedule identical to that used for the vibratory stimulus, so that either the right or the left ear was stimulated. Variance of body sway in the lateral and anteroposterior planes, being proportional to the mechanical energy in the sway, was used to assess postural control2r. The subjects stood erect with the head in the neutral position, both head and trunk facing straight forward during the recordings that were made both with the subject’s eyes open and with them closed. Stutisticul analysis Posturographic test results of the CRC and the nonCRC groups manifested skewed distribution in some tests, and non-normal distribution in others, whereas

The non-CRC group (patients without signs of cervical root compression, n = 18) had significantly higher VAS values for subjective cervical pain intensity, and significantly lower values for active cervical range of motion, compared to the CRC group (patients with signs of cervical root compression, n = 89). The two groups did not differ in sex distribution, age, body height, body weight, duration of symptoms, or incidence of vertigo and unsteadiness(Table 1). Tests of’posturul control Velocity of vibration-induced body sway Figure 2 shows recordings of neck vibration-induced anteroposterior body sway in the eyes closed condition from a patient with cervical root compression and from a healthy subject. The CRC group manifested significantly higher body sway velocities than did the controls in responseboth to calf muscle and to neck muscle stimulation at all frequencies (20, 40, 60 ,80 and 100 Hz) under closed eyes conditions (Figures 3a and 3c respectively). Under open eyes conditions, sway velocities in the CRC group were significantly higher than in controls in response to calf-muscle stimulation at frequencies of 20, 60 and 100 Hz (Figure 3b), and to neck muscle stimulation at frequencies of 60 and 100 Hz

8 7 6 5 E s

4 3 2 I

o

Sway velocity (cm/s)

0 I 0

Figure 1. The distribution of body sway velocities CRC groups, but not in the control group.

in response

to 80 Hz neck vibration

was skewed

in the CRC and non-

Karlberg

et al.: Postural

(Fig. 3d). Differences between the CRC group and the control group in readings for the stimulus-free periods almost reached significance. The non-CRC group also manifested significantly higher body sway velocities than did the controls in response to neck muscle stimulation at all frequencies under closed eyes conditions, at frequencies of 60 and 100 Hz under open eyes conditions, and in one stimulus-free period (Figures 3c and 3d). Sway velocities tended to be higher in the non-CRC group than in the control group in response to calfmuscle stimulation, but the differences did not reach significance. No significant differences were found between the CRC and non-CRC groups in any of the recordings. Identification of characteristic parameters of postural dynamics Values for stij$es.s were significantly lower in the CRC group than in the control group in response to calf muscle stimulation both under open eyes and closed eyes conditions (Figures 4a and 4b respectively), and in response to neck muscle stimulation under open eyes conditions (Figure 4d). Values for dumping were also significantly lower in the CRC group in response to calf-muscle stimulation under open eyes conditions (Figure 4b). The non-CRC group manifested significantly lower sttifizess values in response to calf muscle stimulation under closed eyes conditions (Figure 4a), and lower values for dumping in response to calf muscle stimulation under open eyes conditions, as compared to the controls (Figure 4b). There were no significant differences between the controls and the CRC group or the non-CRC group in values for any of the three characteristic parameters in response to neck muscle stimulation under eyes closed conditions (Figure 4c), or in the values for the srvifiness parameter under any test condition, There were no significant differences between the CRC and non CRC groups in values for any of the three characteristic parameters under any test condition. Variance of vibration-induced body sway

control

with cervicobrachial

pain syndrome

245

(Figure 6). No significant differences were found between the CRC and non-CRC groups under any test condition. Correlation between clinicul dutu und posturul performance. Significant but weak correlations were found in the CRC group between duration of symptoms and velocity of 100 Hz neck vibration-induced body sway in the eyes open condition (r = 0.22, P = 0.04), and the parameter swifness of neck vibration in the eyes open condition (r = 0.25, P = 0.02). Correlations were also found between VAS pain intensity ratings and the parameter st@J+zess in response to calf vibration in the eyes open condition (r = 0.23, P = 0.03), and between cervical range of movement and the parameter swzftness in response to calf vibration in the eyes open condition (r = 0.28, P = 0.01). In the non-CRC group, with a smaller number of subjects, significant inverse correlations were found between cervical active range of movement and 14 of the posturographic measurement values (-0.48 < r c-0.58), and significant positive correlations between VAS pain intensity ratings and nine of the posturographic measurement values (0.48 < r < 0.63) (Table 2). No significant correlations were found between duration of symptoms and the posturographic measurements. Discussion The patients in the present study, selected for their chronic cervicobrachial pain and not because of complaints of vertigo or dizziness, performed significantly poorer than the healthy subjects in objective tests of postural control function. This was found both for the CRC and non-CRC groups, i.e. with versuswithout signs of cervical root compression on MRI. Furthermore the differences in values for the characteristic postural parameters of postural dynamics suggest different dynamics of postural control function in these patients, compared to healthy subjects. No significant

Variance of vibration-induced body sway in the anteroposterior plane was significantly greater in the CRC group than in the control group under all test conditions (Figure 5). No significant differences were found between the non-CRC group and the controls, or between the CRC and the non-CRC groups under any test condition. 80

100

-5 Neck

vibration

(Hz)

Variance of galvanically induced body sway Compared to controls the CRC group manifested significantly greater variance of galvanically induced body sway both in the lateral plane and in the anteroposterior plane, and under both open and closed eyes conditions. The non-CRC group manifested significantly greater variance in the anteroposterior plane under open eyes conditions than did the controls

Figure 2. Body sway reactions in the anteroposterior plane in response to neck vibration, closed eyes condition, for a patient with cervical root compression, and a healthy subject. The patient reacts to the vibration periods with more marked movements and greater oscillations.

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“. s.

“. 5. ‘T

0 stimulus

20 Hz

40 Hz

60 Hz

T

*

60 Hz

B. Calf vibration -eyes open

3

0 100 Hz

0 stimulus

l

Neck vibration

t t

3

l l

0 stimulus

20 Hz

40 Hz

6oHz

60 Hz

Ti

100 HZ

0

20 Hz

60 Hz

D. Neck vibration - eyes open

0 stimblus

20 Hz

T

60 Hz

T

60 Hz

100 Hz

Vibration fr=VJenCY

I

Vibration 100 Hz fr’TJancY

Figure 3. Velocities of vibration-induced body sway with vibration towards the calf muscles with closed eyes (A) or open eyes (B), and vibration towards the neck muscles with closed eyes (C) or open eyes (D). The patients in the CRC and nonCRC groups manifested higher body-sway velocities both with closed and with open eyes than did controls. There were no significant differences between the CRC and non CRC groups. Means and SEM are given. Levels of significance are denoted by asterisks: *P c 0.05, **P c 0.01, *** PcO.001.

differences in postural control performance were found between the two patient groups. About 50% of the patients complained of vertigo or dizziness, a frequency higher than that reported for the population in generals*, but in accord with earlier reports of vertigo in patients with cervical spondylosiss. Several significant correlations between posturographic test results and pain intensity or cervical range of movement were found in the non-CRC group, but not in the larger CRC group. This suggeststhat the two groups may have differed in the aetiology of their postural disturbance, or in their reaction to similar lesions. Hypothetically, the impact of cervical pain and cervical range of motion on postural performance in the patients with root compression may be concealed by disturbed cervical proprioception due to compression of the dorsal roots, or by subclinical pressure on the spinal cord. Several animal studies have shown information relayed in the cervical dorsal roots, most significantly C-C,, to be important for postural control’. In man, however, cervical root compression is most common at the C,-C, level39, and this was also true of the patients in the present study. Narrowing of the cervical canal

exerting pressure on the spinal cord would reasonably be accompanied by symptoms from the long spinal tracts. The present group of patients with root compression manifested no such symptoms. However, pressure on the spinal cord in certain head positions cannot be ruled out as the MRI scans in the present study were performed with the head in the neutral position. MRI scans of the cervical region during extension or flexion of the neck can show protrusive lesions compressing the spinal cord, whereas scans with the head in the neutral position only shHow a narrowing of the spinal cana133. However, in the present study the posturographic tests were also performed with the head in the neutral position. Recently it has been proposed that increased muscular tension via inflammatory mediators and metabolites can sensitize proprioceptive as well as nociceptive receptor+. Cervical pain may induce increased muscular tension; and as this increased tension, and hence the concentration of metabolites, may be unequally distributed in the cervical muscles, the proprioceptors will be unequally sensitized as well. This may result in erroneous proprioceptive information from the cervical muscles. If proprioceptive information is erroneous, its

Karlberg

ef al.: Postural

‘* A Calf vibration 1-eyes closed

‘* 10

10

0

Swiftness

control

1

Stiffness

Damping

0

with cervicobrachial

pain syndrome

B. Calf vibration -eyes open

Swiftness

Damping

Stiffness

1.6 (0.2)

2.0

(0.2)

9.4

(0.6)

2.6

(0.4)

0 Controls (n=20) B ‘CRC’ group (n=89)

2.5 (0.2)

5.7 (0.9)

2.7 (0.1)

3.9 (0.2)

1.4 (0.1)

2.3

(0.1)

7.2

(0.4)

2.1

(0.1)

q

3.0

3.7 (0.3)

1.6

2.3

(0.1)

6.2

(1.1)

2.0

(0.2)

‘nonCRC’ group (n=l8)

(0.1)

(0.1)

D. Neck vibration -eyes open

C. Neck vibration -eyes closed

0

0 q

Swiftness

Controls (n=20) ‘CRC’ group (n=89)

Gl ‘nonCRC’ group (n=l8)

3.0

(0.3)

Stiffness

Damping

247

Swiftness

T

Stiffness

n

Damping

4.5 (0.4)

2.1 (0.4)

2.0

(0.2)

3.4

3.9 (0.2)

1.6 (0.1)

2.3

(0.1)

2.6 (0.5)

7.0 (2.4)

2.5 (0.6)

2.3 (0.1)

2.3 (0.4)

(0.9)

Figure 4. Values for characteristic parameters of postural dynamics for vibration towards the calf muscles, in closed (A) or open eyes (B) conditions, and vibration towards the neck muscles, in closed (C) or open eyes (D) conditions. The CRC group differed significantly from the controls with lower values for stiffness (A, B and D) and damping(B). The non-CRC group differed significantly from the controls in values for stiffness (A) and damping (B). There were no significant differences between the CRC and non-CRC groups. Means and SEM are given. Levels of significance are denoted by asterisks: *PC 0.05, **PC 0.01, ***PC 0.001.

Figure 5. Under all test conditions (i.e. under both open and closed eyes, and both with calf and with neck muscle stimulation), the CRC group manifested significantly greater variance of vibration-induced body sway in the anteroposterior plane than did controls. No significant differences were found between the non CRC group and the controls, or between the CRC and non-CRC groups. Means and SEM are given. Levels of significance are denoted by asterisks: *PC 0.05, **PC 0.01, ***PC 0.001.

Figure 6. Both under open and under closed eyes conditions, the CRC group manifested significantly greater variance of galvanically induced body sway in the lateral and the anteroposterior planes than did controls. The non-CRC group manifested significantly greater variance than the control group only with closed eyes in the anteroposterior plane. There were no significant differences between the CRC and non-CRC groups. Means and SEM are given. Levels of significance are denoted by asterisks: *PC 0.05, **PC 0.01, ***PC 0.001.

248

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Posture1995;3:

Table 2. Correlation posturographic results

No 4

between clinical in the non-CRC group

VAS pain intensity r value (Pvalue)

data and (n = 18).

Cervical range of movement r value (Pvalue)

Calf vibration Closed eyes No stimulus 20 Hz 40 Hz 60 Hz 80 Hz 100Hz

0.50 0.40 0.47 0.44 0.46 0.41

(0.04) (n.s.1 (0.05) (n.s.) (n.s.) (n.s.1

-0.51 -0.36 -0.55 -0.49 -0.58 -0.44

(0.03) (n.s.) (0.02) (0.04) (0.01)

Open eyes No stimulus 20 Hz 40 Hz 60 Hz 80 Hz 100 Hz

0.41 0.42 0.43 0.40 0.45 0.39

(n.s.1 (n.s.) (n.s.) (n.s.) (n.s.1 (n.s.1

-0.27 -0.19 -0.45 -0.45 -0.57 -0.48

(n.s.1 (n.s.1 (n.s.) (n.s.) (0.01) (0.05)

(0.03) (0.03) (n.s.1 (n.s.1 (0.04) (n.s.1

-0.33 -0.33 -0.43 -0.42 -0.34 -0.35

(n.s.1 (n.s.1 fn.s.1 (n.s.1 (r7.s.) (n.s.)

(n.s.1

-0.52

(0.04)

(n.s.1

-0.52

(0.04)

(n.s.) (0.05) (n.s.1 (0.02) in.s.1 (0.051

-0.25 -0.24 -0.49 -0.48 -0.50 -0.43

(n.s.1 (n.s.1 (0.04) (0.04) (0.03) (t7.s.)

(n.s.)

-0.52

(0.04)

(n.s.1 (0.007)

-0.53 -0.33

(0.04) (n.s.1

Neck vibration Closed eyes No stimulus 0.53 20 Hz 0.53 40 Hz 0.47 60 Hz 0.47 80 Hz 0.48 100 Hz 0.47 Lateral sway variance 0.33 Anteroposterior sway variance 0.39 Open eyes 0.45 0 stimulus 0.46 20 Hz 40 Hz 0.45 60 Hz 0.53 80 Hz 0.44 100 Hz 0.46 Lateral sway variance 0.31 Anteroposterior sway variance 0.37 Damping 0.63 Galvanic stimulation Open eyes Anteroposterior variance

sway 0.33

(n.s.)

-0.57

(n.s.1

(0.03)

convergence with correct vestibular information in the CNS9 can give rise to a sensory mismatch41. This may be the common cause of sensationsof vertigo and dizziness in cervical pain syndromes of different origin, and may explain the results for the non-CRC group. There is a possibility that pain per se might affect postural control function, but Revel and co-workers found no correlation between the intensity of cervical pain and the degree of impaired cervicocephalic kinaesthesials. Moreover, dizziness and vertigo is not reported to be a prominent symptom in other chronic pain syndrome+. It would be interesting to compare the

present chronic cervicobrachial pain population, especially the non-CRC group, with a group of patients with other chronic pain syndromes. However, it is hard to find a suitable group as many pain syndromes involve the postural muscles, and chronic facial pain or headache may induce increased tension in the cervical muscles. Restriction of cervical motion by a cervical collar is reported to impair postural control in healthy subject+. Cervical range of motion was assessedin the patients, being found to be within the lower normal range. No comparisons were made with the normal subjects, as cervical range of motion manifests great interindividual variation and normative values differ from study to study43. Furthermore, as cervical range of motion and cervical pain are closely related, it is hard to distinguish their separate effects on postural control function. The patients might be expected to deliberately perform poorer than the healthy subjects in the postural tests, in order to obtain faster help; and malingering is a potential source of error when patients are compared with healthy subjects. However, if a subject tries to perform poorly in the posturographic tests, this usually gives rise to a pattern of high-frequency body sway, unaffected by the vibratory stimulation and easily recognized by the examiner. In the present study one patient was excluded because of such suspicions. Furthermore, had this source of error had a substantial impact on the results, then sway velocities in the stimulus-free periods would also be expected to differ between the patients and the controls, which they did not. With the exception of analgesicsof the NSAID type, the patients were requested not to take any medications for 24 h before the test, an instruction that was observed as far as could be ascertained. As few of the patients were on continuous medication with sedatives, in all likelihood any transient withdrawal effects on the results would have been minimal. Conclusions Patients with chronic cervicobrachial pain syndrome have impaired postural control, compared to healthy subjects. The results suggestthat cervical lesions such as a root compression may impair postural control. Disorders of the neck should be considered when assessing patients complaining of dizziness, vertigo, and balance disturbances. Acknowledgements The help of Professor Carl-Axe1 Carlsson in initiating the study is gratefully acknowledged. This study was supported by the Swedish Medical Research Council (grant no. 17X-05693), the Medical Faculty of the University of Lund, the Malmijhus County Council Care Committee, the Einar Bjijrkelund Foundation, the Elsa Smitz Foundation, and the Swedish Society for Medical Research.

Karlberg

et al.: Postural

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