- Email: [email protected]
Electronic pressure algometry of deep pain in healthy volunteers
526
Electronic Pressure Algometry of Deep Pain in Healthy Volunteers Jean-Jacques
Vatine, MD, Shmuel C. Shapiva,
MD, Flovella Magova,
MD, David Adlev, MSc, Alexandev
Magova,
MD
ABSTRACT. Vatine JJ, Shapira SC, Magora F, Adler D, Magora A: Electronic pressure algometry of deep pain in healthy volunteers. Arch Phys Med Rehahil 1993;74:526-30. l Deep pressure pain threshold (PPT) and pressure pain tolerance (PPtol) were measured by pressure algometry at the mastoid processes, external malleoli, and sternum in 24 healthy volunteers. The algometer consisted of a force displacement transducer with a 0.25cm2 pressure tip linked to a recorder. The rate of force application was approximately 1kg/sec/0.25cm2. High intersubject variation was noted at all sites for both PPTand PPtol. Mean PPT and PPtol values at the sternum were 5.2kg + 2.1 and 8.lkg k2.4, respectively, and significantly higher than at the other sites. PTT did not differ significantly between the sexes or between dominant and nondominant sides. PPtol, on the other hand, was lower in the women, but significantly so only at the malleoli. On repeat examination, comparison between the mean values at each site showed no statistical differences in any instance. Pressure algometry, as used in this study in healthy subjects, proved a reliable technique for the estimation of deep PPT and PPtol values. It may possibly serve for screening the response to experimental pain in various groups of pain patients. 10 1993 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and
Rehabilitation
Local tenderness to pressure is a major manifestation of many types of musculo-skeletal syndromes, as well as some visceral disorders. Because pain is a multidimensional, subjective sensation, a quest for its quantification based on the response to experimental electrical, thermal, and pressure stimuli has been pursued for many years. The application of pressure, unlike other techniques, has the obvious advantage of triggering the same type of nociceptors as does palpation during clinical examination of tenderness. Force application as an experimental stimulus seems therefore an appropriate technique for the quantitative determination of pain threshold and pain tolerance.‘-3 After the first trials of pain response to pressure,4-6 commercially available metal disc and other algometers were introduced into clinical use. ‘5’ Their major disadvantages were inexact measurement of the applied force, variable surfaces of examination, irregular increase of pressure, and/ or lack of precise relation between increment of pressure and time. Another drawback was the time lag between the subject’s verbal expression of pain and the examiner’s reaction in recording the painful force, with resultant marked variations in sensitivity value readings. This, in turn, led to high intrasubject and interrater variability, with poor reproducibility and nonquantifiable results.‘,” The electronic pressure algometers developed lately correct some of these shortcomings by using precise quantification of force/time measurement. In addition, the time From the Departments of Physical Medicine and Rehabilitation (Drs. Vatine and A. Magora), Anesthesiology (Drs. Shapira. F. Magora). and Biomedical Engineering (Mr. Adler). Hadassah University Hospital. Jerusalem, Israel. Submitted for ouhlication December IX. I99 I, Accepted in rewed form June 8. 1992. Reprint requests to J. J. Vatine. MD. Department of Physlcal Mrchcine and Rehabilitation, Hadassah University Hospital. Mount Scopus, PO Box 24035, Jerusalem 9 1240. Israel. c lY93 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation OOO3-9993/93/7405-O I90$3.00/0
Arch Phys Med Rehabil Vol74, May 1993
lag inherent in the verbal mode to signal pain perceptions is eliminated by the use of a subject-operated push button that activates the marker of a recorder.“s’2 Using these instruments for skin and muscle pressure algometry yielded reliable interrater and test-retest results in various population samples.‘,‘3 They also showed clinical utility, in that they provide an additional measure of evaluation in syndromes characterized by muscle and deep tissue tenderFor instance, Tunks and colleagues’ demonness. 9~“~14~‘5 strated diffuse lowering of pain thresholds in chronic fibromyalgia patients, claiming that the pain threshold of nontender points in these patients discriminated between them and healthy subjects. Increased sensitivity to induced pain may accompany other conditions in which deep pain is a major manifestation, such as trigeminal neuralgia, angina pectoris, and chronic tension type headache.16-19 Lately it was reported that, although individual values were widely scattered, pressure pain thresholds were, on the average, significantly lower in chronic tension type headache, both at the pericranial sites and over the Achilles tendon.” The deep pain of bone and periosteum has not been investigated systematically. The rationale for using periosteal sensitivity is justified by the fact that pain originating in the periosteum forms part and parcel of numerous musculoskeletal disorders.“,” Furthermore, stimulation of the periosteal nociceptors is used clinically to assess deep sensation during neurological examination.” Lastly, the examination of bony areas permits placement of the algometer on a well defined and circumscribed area, thus preventing the interference of technical artefacts arising from the movement of soft tissue that may occur with pain measurement over muscles.23 In other words, using bony areas for assessment of pain will improve the reliability of the examination, a need that has been stressed by other investigators.13 Quantification of the response of bony areas to pressure may provide a reliable dimension for comparing pain threshold and
DEEP PAIN PRESSURE ALGOMETRY, tolerance between various groups of pain sufferers. It may also assist in studying the effect of therapy on sensitivity to evoked pain. The purpose of this study was to define parameters of deep pressure pain measurements in healthy subjects, so as to provide a basis for comparison with future investigations of patients suffering from various pain syndromes. The following report presents the results of pressure algometry examinations carried out on five bony locations in healthy \ olunteers. using an electronic push-button algometer.
MATERIALS
AND
METHODS
Pressure algometry was applied in 24 healthy volunteers ( 14 men and 10 women. aged 20 to 40 years) after informed
consent and approval of the protocol by the Hospital Ethics Committee. None of the subjects suffered from any systemic disease or pain syndrome, and all were right-hand dominant. The instructlons for signalling onset of pain (threshold) and unacceptibility of pain (tolerance) were identical for all participants. In this study, the pressure algometer. which has been described previously. ” consisted of a commerciallv available force-displacement transducer.” with the following. easily constructed. modifications: ( I ) a round, teflon tip with an area of 025cm’ attached to one of the beam shafts of the transducer. and (2) an aluminum handle mounted on the transducer to facilitate continuous pressure on the selected anatomical point. The modified algometer is connected to an amplifier” that is plugged into a two-channel recorder’ equipped with a time marker linked to one channel (fig 1). ‘The marker is activated by the subject via a hand-held push
Vatine
527
button, thus eliminating the verbal subject-examiner delay, and affording instantaneous recording of the pain response signals. The force was applied to increase from 0 to 1Okg in IOsec and to produce a deflection of 5mm/kg on the other channel of the recorder. Recording speed was Smm/sec. This range of force increment proved optimal for the subjects, as well as a convenient rate of increase in force application for the examiner. At the sa.me time. it prevented undue prolongation of pressure with potential persistence of pain and tissue damage. Typically after only a short practice. the examiner becomes skilled In applying force increments at the controlled rate of 1kg/set. The visualization of the force signal on the recorder nol. only assists the examiner in attaining this skill, but also shows the constancy of the rise in pressure during each examination (fig 3). The osseus locations chosen for the pressure pain examinations were the mastoid processes and the external malleolus bilaterally, and the sternum measured at two adjacent points (7 and 9cm below the upper border on the midline), in order to avoid evaluation of pararneters from an immediately previously sensitized area. These two points were considered a single site of measurement. These sites lack overlying muscle, are covered by little t%t tissue. and constitute well circumscribed areas. The sites were examined following a fixed order: sternum, right mastoid. right external malleolus. left external malleolus, left mastoid, and sternum. One complete test required approximately ten minutes. The second test was performed one hour after the first one, using the same order of exammation. Although not a randomized method, it permitted variations in the time interval between the two measurements carried out at the sternum. Thus. the time interval between the two sternum
Fig I-The pressure algometry apparatus. A, pressure transducer: B, self-activated subject push button; C, two-channel recorder. Arch Phys Med Rehabil Vol74, May 1993
DEEP PAIN PRESSURE ALGOMETRY,
528
Vatine
Pressure pain threshold (PPT = onset of perception of pain) and tolerance to pain (PPtol = pain becoming unacceptable) were measured at each site of interest. The calculated difference between PPT and PPtol provided the range of sensitivity to pain (RSP). The results of the pressure algometry determinations are expressed in kilograms per 0.25 square centimeters. For comparison between sites, the mean values at the sternum were based only on the first examination values obtained in the two tests, in order to retain the same number of samples (48) in each group. The mean values for either sex group are based on four individual examinations, ie, two at each mastoid process, two at each malleolus and four at the sternum. Thus, the mean values at the mastoid process, malleolus, and sternum reflect 56 measurements for the 14 men and 40 measurements for the 10 women. For comparison of the right (dominant) side with the left side, only the values for the mastoid process and external malleolus were used. The values of the two tests for each lateralized site were pooled for all 24 subjects, that is, calculations for each of the parameters encompass the values of 48 examinations. Statistical
A A force applied at the sternum. Lower tracing: time marker. Arrows indicate markings of pain pressure threshold (FIT) and pain pressure tolerance (PPtol). Fig Z-Upper
tracing: pressure
recording from
pressure examinations during the same test was occupied by the measurements taken at the four other sites. whereas the interval between the second examination of the first test and the first examination of the second test was one hour. Table 1: Individual Pressure Algometry Values at the Sternum in 24 Volunteers (in kg/O.25 cm’) Age
Ses
Yl-f
31 52
F F F F F F F F F F M M M M M M M M M M M M M M
6
34 36 30 32 46 29 62 21 60 40 17 33 40 30 33 45 34 60 33 34 57 34
3.4 7.6 5.0 8.0 4.8 2.6 2.4 4.6 7.0 6.8 4.4 X.8 8.8 4.6 4.2 2.2 I.6 2.R 9.0 6.X X.0 3.6 7.0
Arch Phys Med Rehabil Vol74, May 1993
PPtol
RSP
7.4 7.2 8.6 5.8 10.0 5.0 IO.2 X.0 6.5
1.4 3.8 1.0 0.X 2.0 0.2 7.6 5.6 1.9 3.0 2.8 2.8
10.0
9.6 7.2 10.0
IO.0 11.0
8.8 2.6 4.3 4.X
I I.5 9.2 11.5 9.2 12.X
I.2 1.1 6.4
4.6 0.4 2.7 2.0 2.5 2.4 3.5 5.6 5.8
Analysis
Standard methods were used for descriptive statistics. For each measurement group (site, sex, side) the mean values and standard deviations were calculated. The significance of the difference between the means of two groups was tested by the randomization test for two independent samples. This test was chosen because it does not assume normal distributions or homogeneity of variance in the population involved. For all tests, p < 0.05 was considered significant.
RESULTS The values obtained at the sternum, mastoid processes and external malleoli showed large interindividual PPT and PPtol differences in both tests. Table 1, which presents the measurements at the sternum, exemplifies the wide range in parameter values. Table 2 lists the mean (t SD) values for PPT, PPtol, and RSP at all examined sites. The PPT values at the sternum were significantly higher than at the other sites tested, except for the right external malleolus. Table 2: Mean (LSD) Pressure Algometry Values According to Site (in kg/O.25 cm’)
Site
Pressure Pain Threshold I + + + f
2. I 1.9* 1.5* 2.1” 2.0*
Sternum Right mastoid Left mastoid Right malleolus Left malleolus
5.2 3.6 3.5 4.6 4.5
11represents comparison sites tested. * p < 0.00 I. ‘1’ < 0.01. *p i 0.5. ” p > 0.5 (nonsignilicant).
between the sternum
Pressure Pain Tolerance
Range of Sensitivity to Pain
7.9 + 1.X 2.6 7.6 2.3 2.3
i + ~ + _ t
1.61i 7 0” _. -J 0” _. 1.8”
values and each of the other
DEEP PAIN PRESSURE
PPtol values at the sternum were significantly higher than at all other sites. The RSP at the sternum was similar to that measured at the other sites. The mean pressure values obtained in the first test for each of the parameters at each site showed a persistent similarity with the respective values of the second test. In no instance were the intertest differences statistically significant (table 3). Table 4 presents the comparison between the pressure algometry values according to sex for all sites and parameters examined. The mean PTT \,alues for each of the examined points did not show significant gender differences. The mean PPtol values for the external malleolus in the women was, however, significantly lower (JI < 0.02). Mean RSP values were significantly lower in the women (mastoid p < 0.05. malleolus 11< 0.0 1) with the exception of the sternum, which showed similar values in both sexes. The mean values for the right (dominant) and left side did not differ significantly for either the mastoid process or the external malleolus (table 5).
DISCUSSION The high degree of intersubject difference in pain threshold and pain tolerance pressure algometry values determined at the same site noted in the present study is consistent with reports by other investigators,““-7.‘3.‘4 notwithstanding the rather small number of our subjects and their narrow age range. It is commonly accepted that the intersubject differences of sensitivity to pain arise in both the organic sensory dimension and the reaction component of the subject.” The differing somatic sensitivity to pain, the personality and emotional state of the subject. his interpretation of the instructions. or familiarity with the test after repeated examinations may all influence the results. This intersubject variability constitutes an unavoidable limitation of pressure algometry. However, the similar mean values recorded in this study at each of the sites for all three parameters in both first and second series of examinations showed the method to be reproducible and appropriate for comparison of groups. The unexpectedness of the discomfort elicited by the Table 3: Intertest Comparison of Pressure Algometry Values (mean t- SD) Obtained at the Examined Sites (in kg/O.25 cm*)
Test ILO.
Site - ____~~~
I 1 T 4 I
Stunurn
Right
mastold
3
Lcti mastoid Right
T 3
malleolus
I ct.1malleolu~ ~ -__.
~_.
11is nonsignlticant
T 3 ; 2
Pressure Pain Threshold
Pressure Pain Tolerance ___~
5.5 + 2.3 3.x t I.9 4.h -c 7. I 5.1 i 2.1 3.5 + I.‘)
8.1 i 2.1 7.5 t- 2.5 8.6 k I.7 8.0 f 2.h
3.7 3.4 3.5 4.5 4.7 4.7 4.x
tbr all intertest
L 2.0 + I.5 -t I.5 t ‘.O i 7.2 L? I.9 i 2.0
6.3 6.0 6.1 5.9 6.6
+ 2.5 + 2.3 -+ 2.7 t 2. I i 2.x 7.0 * 7.7 0.7 ?I 2.7 0.9 i 2.3
\aIues at any ofthe
Range af Sensitivity to Pain
3.0 t 2.1) 2.6 + 1.6 3.0 + 7.0 I.9 1.8 2.3 7.7
+ + * *
2.5 i ‘.I 2.3 3.5 2.1
-t -t L -t
examined sites.
1.3 I.5 I.6 2.1 1.7 I.9 1.6 3.3 2.1
ALGOMETRY,
Vatine
Table 4: Comparison of Pressure Algometry Values (mean f SD) Obtained at the Sites Examined According to Sex (in kg/O.25 cm2) __-____ I’emale (n z 101 .___
Male
Parameter
Site
5.2 + ” Sternum 3.3’17? hlastoid process hlalleolus 4.6 ? 2 I x.x + 3 5 Sternum Mastoid process (1.3 ? 3 7 7.4 L 2.7 Malleolus Sternum I.8 .I._‘i hlastoid process 7.‘) I I.Y ?q+lT Malleofus _.C _ -.______-._
I' f'T PPtol
RSP
Ahbre\iation:
(II = 14) _______~_
i3? :;
p Value
I.‘, ;_ 1:;
+
7 x 5 x 0 I1 2s 2 2 _.
f 1,s i 2.1 _(12.1 -1.’ +. I.5 16: I.1
NS. nonsignificant.
pain during the first examination has been mentioned by others as a possible cause for lowering the pain threshold.‘.“.’ ‘.I4which may explain the large interest variability. However. the similar values that were recorded at the sternum. irrespective whether examined as first (first examination of the first test) or as last point (second examination of the second test). seem to imply that familiarity with this technique is not a determinant in the response to applied force. The absence of overlying muscle and the scant fat tissue at the three osseus areas chosen in this study afforded a near direct response of bone to pressure stimuli with minimal interference. Contrary to the assumption that periostal sensitivity to pain would be similar at all locations studied. the pressure algometry values at the sternum proved signilicantly different from those recorded at the mastoid process and external malleolus in the two successive tests. The notable elevation of PPT and PPtol at the sternum and the high sensitivity to pain in the mastoid area could be ascribed to varying degrees of sensory innervation and the differing proportions of local nociceptive receptors. Similar persistent differences in response to pain stimuli between sites have been reported previously. especially with regard to muscle versus bone measurements.‘,“.‘5 These findings underscore once again that meaningful interpretation of reaction to pain is only possible if comparable anatomical sites are used for evaluation. For further elucidation of sensitivity to pain, the sternum is advised as the most suitable testing site. First of all, by virtue of the sternum’s low sensitivity. the influence ofthe Table 5: Comparison of Pressure Algometry Values (mean t SD) According to Side (in kg/O.25 cm2) -_-_ ___ Parameter
Site
Pressure pain threshold
Mastold procrs\ Malleolus Mastold process Malleolus Mastoid process Malleolus
Prcssurc pain tolerance Range ofscnsitivit! to pain 11is nonslgniiicant
Right (4% tests) 2.h t 4.6 k t.2 t r.Sk27 I’.0 * :.3+20
I x 2 I 2 5 I 5
._
I,eft (48 tests) 3.5 t
I.5 1.Y t 2.5 ? 2.5 + 1.x +- 1.x .~
4.4 + 6.0 6.X 2.5 2.3
for the three parameters in all inrtanccx
Arch Phys Med Rehabil Vol74, May 1993
DEEP PAIN PRESSURE ALGOMETRY, Vatine
530 variable time reaction component
is proportionally minimized in this bony area: secondly, the relatively large flat surface of the sternum permits stable contact between bone and algometer tip, thus enhancing the exactitude of the results. A number of investigators7,‘5*‘6,27reported a markedly higher sensitivity (lower PPT and PPtol) to pain in women. The present study did not reveal significant differences in PTT between the sexes (table 4). Our results demonstrate a statistically significant higher male PPtol for all sites examined. The fact that the difference in PPtol between the sexes was significant only at the malleolus, may be explained by the relative small number of subjects entered into the study. Some studies’5,‘8,‘9 found a relationship between lateral dominance and sensitivity to pain. No such dominance-related difference in response to the pressure stimuli was noted in our subjects (who were all right-handed), which concurs with results from other research.“22 These contradictory findings regarding laterality and pain response are probably due to selection of sites or the method of examination used. Although pressure algometry is a simple, noninvasive technique for the assessment of perception of force-induced pain, many equipment, examiner, and subject-related variables may interfere with the precision of the obtained measurements. To enhance reproducibility of the results, we used an algometer with a fixed area of pressure, controlled force, and application time, and with direct transference of the subject’s reaction. The serial measurements, analyzed independently for each of the bony areas studied, showed the technique to be reliable. Pressure algometry applied at nontender points may prove valuable for a better understanding of pain behavior in patients suffering from conditions characterized by severe pain, and, in turn, may contribute to their treatment. The technique and observations of the present study may be useful as a basis for comparing the responses to deep pain in various groups of pain patients. References
I. Fischer AA. Pressure tolerance 2. _3
4.
9.
over muscles and bones in normal subjects. Arch Phys Med Rehabil 1986;67:406-9. Tunks E. Crook J, Normann G, Kalaher S. Tender points in ftbromyalgesia. Pain I988:34: 1 1-9. Yunus MB, Kalyan-Raman UP, Kalyan-Raman K. Primary fibromyalgesia syndrome and myofacial pain syndrome: clinical features and muscle pathology. Arch Phys Med Rehabil 1988;69:45 1-4. Libman E. Observations on individual sensitiveness to pain with special reference to abdominal disorders. JAMA 1934:102:335-41. Pelner L. The determination of sensitivity to pain. J Lab Clin Med 1941;27:248-51. Keele KD. Pain sensitivity tests, the pressure algometer. Lancet 1954: 1:636-9. Merskey H. Spear FC. The reliability of the pressure algometer. Br J Sot Clin Psycho1 1964;3: 130-6. McCarthy DJ Jr. Gatter RA, Phelas P. A dolorimeter for quantification of articular tenderness. Arthritis Rheum 1965;8:55 1-9. Williams RC. Toward a set of reliable and valid measures for
Arch Phys Med Rehabil Vol74, May 1993
chronic pain assessment and outcome research. Pain 1988;35:239-5 1. IO. Chapman CR, Casey KL, Dubner R, Foley KM, Gracely RN. Reading AE. Pain measurement: an overview. Pain 1985; 22:1-31. 11. Jensen K, Andersen HO, Olesen J, Lindblom U. Pressurepain threshold in human temporal region. evaluation ofa new pressure algometer. Pain 1986:25:3 13-23. 12. Adler D, Magora F. Shapira SC. Veler A, Mahler Y. A new recording pressure algometer. Pain Clin 199 1:4: 183-6. 13. Brennum J, Kjeldsen M. Jemsem K, Jensen TS. Measurements of human pressure-pain thresholds on fingers and toes. Pain 1989:38:2 1 l-7. 14. Jaegger B, Reeves JL. Quantification of changes in myofacial trigger point severity with the pressure algometer following passive stretch. Pain 1986;27:203- 10. 15. Fischer AA. Pressure algometry over normal muscles. standard values, validity and reproducibility of pressure threshold. Pain 1987;30: 1 15-26. 16. Hampf G, Bowsher D, Wells C, Miles J. Sensory and autonomic measurements in idiopathic trigeminal neuralgia before and after radiofrequency thermocoagualation: differentiation from other causes of facial pain. Pain 1990:40:241-S. 17. Droste C, Greenlee MW, Roskamm N. A defective angina pectoris pain warning system: experimental findings of ischemit and electrical pain test. Pain 1986;26: 199-209. 18. Pedersen F, Pietersen A, Madsen JK. Ballegaard S, Meyer C, Trojaborg W. Elevated pain threshold in patients with effortinduced angina pectoris and asymptomatic myocardial ischemia during exercise test. Clin Cardiol 1989: 12:639-42. 19. Schoenen J, Botton D, Hardy F, Gerard P. Cephalic and extracephalic pressure pain thresholds in chronic tension-type headache. Pain 199 1;47: 145-5 1. 20. Harkness JAL. Higgs ER. Dieppe PA. Osteoarthritis. In: Wall PD. Melzack R. eds. Textbook of pain. Edinburgh: Churchill Livingstone. 19842 15-24. 21. Yates A, Smith MA. Musculo-skeletal pain after trauma. In: Wall PD. Melzack R, eds. Textbook of pain. Edinburgh: Churchill Livingstone. 1984:234-9. 22. Adams RD, Victor M. Other somatic sensations. In: Principles of neurology. New York: McGraw-Hill, 1985: 114-28. 23. Fischer AA. Pressure tolerance over muscles and bones in normal subjects. Arch Phys Med Rehabil 1986;67:406-9. 24. Merskey H. Gilhs A, Marszalek KS. A clinical investigation of reactions to pain. J Ment Sci 1962;108:347-55. 25. Magora A. Vatine J-J, Magora F. Quantification of musculoskeletal pain by pressure algometry. Pain Chn 1982:5: 10 l-4. 26. Dundee JW. Moore J. Alterations in response to somatic pain associated with anaesthesia. an evaluation of a method of analgesimetry. Br J Anaesth 1960:32:396-406. 21. Ohrbach R, Gale EN. Pressure pain thresholds, clinical assessment and differential diagnosis: reliability and validity in patients with myogenic pain. Pain 1989;39: 157-69. 28. Haslam DR. Lateral dominance in the perception of size and of pain. Q J Exp Psycho1 1970;22:503-7. 29. Wolff BB. Jarrik ME. Relationship between superficial and deep somatic thresholds of pain with a note on handedness. Am J Psycho1 1964:77:589-99. Suppliers
a. b. C.
node1 FT 10, Grass Medical Instruments, 10 1 Old Colony Aveue, Quincy, MA 02 169. dodel 8805, Hewlett Packard Company, 4 Choke Cherry :oad, Rockville. MD 20850. /lode1 7702B. Hewlett Packard Company, 4 Choke Cherry Load, Rockville, MD 20850.
Electronic Pressure Algometry of Deep Pain in Healthy Volunteers Jean-Jacques
Vatine, MD, Shmuel C. Shapiva,
MD, Flovella Magova,
MD, David Adlev, MSc, Alexandev
Magova,
MD
ABSTRACT. Vatine JJ, Shapira SC, Magora F, Adler D, Magora A: Electronic pressure algometry of deep pain in healthy volunteers. Arch Phys Med Rehahil 1993;74:526-30. l Deep pressure pain threshold (PPT) and pressure pain tolerance (PPtol) were measured by pressure algometry at the mastoid processes, external malleoli, and sternum in 24 healthy volunteers. The algometer consisted of a force displacement transducer with a 0.25cm2 pressure tip linked to a recorder. The rate of force application was approximately 1kg/sec/0.25cm2. High intersubject variation was noted at all sites for both PPTand PPtol. Mean PPT and PPtol values at the sternum were 5.2kg + 2.1 and 8.lkg k2.4, respectively, and significantly higher than at the other sites. PTT did not differ significantly between the sexes or between dominant and nondominant sides. PPtol, on the other hand, was lower in the women, but significantly so only at the malleoli. On repeat examination, comparison between the mean values at each site showed no statistical differences in any instance. Pressure algometry, as used in this study in healthy subjects, proved a reliable technique for the estimation of deep PPT and PPtol values. It may possibly serve for screening the response to experimental pain in various groups of pain patients. 10 1993 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and
Rehabilitation
Local tenderness to pressure is a major manifestation of many types of musculo-skeletal syndromes, as well as some visceral disorders. Because pain is a multidimensional, subjective sensation, a quest for its quantification based on the response to experimental electrical, thermal, and pressure stimuli has been pursued for many years. The application of pressure, unlike other techniques, has the obvious advantage of triggering the same type of nociceptors as does palpation during clinical examination of tenderness. Force application as an experimental stimulus seems therefore an appropriate technique for the quantitative determination of pain threshold and pain tolerance.‘-3 After the first trials of pain response to pressure,4-6 commercially available metal disc and other algometers were introduced into clinical use. ‘5’ Their major disadvantages were inexact measurement of the applied force, variable surfaces of examination, irregular increase of pressure, and/ or lack of precise relation between increment of pressure and time. Another drawback was the time lag between the subject’s verbal expression of pain and the examiner’s reaction in recording the painful force, with resultant marked variations in sensitivity value readings. This, in turn, led to high intrasubject and interrater variability, with poor reproducibility and nonquantifiable results.‘,” The electronic pressure algometers developed lately correct some of these shortcomings by using precise quantification of force/time measurement. In addition, the time From the Departments of Physical Medicine and Rehabilitation (Drs. Vatine and A. Magora), Anesthesiology (Drs. Shapira. F. Magora). and Biomedical Engineering (Mr. Adler). Hadassah University Hospital. Jerusalem, Israel. Submitted for ouhlication December IX. I99 I, Accepted in rewed form June 8. 1992. Reprint requests to J. J. Vatine. MD. Department of Physlcal Mrchcine and Rehabilitation, Hadassah University Hospital. Mount Scopus, PO Box 24035, Jerusalem 9 1240. Israel. c lY93 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation OOO3-9993/93/7405-O I90$3.00/0
Arch Phys Med Rehabil Vol74, May 1993
lag inherent in the verbal mode to signal pain perceptions is eliminated by the use of a subject-operated push button that activates the marker of a recorder.“s’2 Using these instruments for skin and muscle pressure algometry yielded reliable interrater and test-retest results in various population samples.‘,‘3 They also showed clinical utility, in that they provide an additional measure of evaluation in syndromes characterized by muscle and deep tissue tenderFor instance, Tunks and colleagues’ demonness. 9~“~14~‘5 strated diffuse lowering of pain thresholds in chronic fibromyalgia patients, claiming that the pain threshold of nontender points in these patients discriminated between them and healthy subjects. Increased sensitivity to induced pain may accompany other conditions in which deep pain is a major manifestation, such as trigeminal neuralgia, angina pectoris, and chronic tension type headache.16-19 Lately it was reported that, although individual values were widely scattered, pressure pain thresholds were, on the average, significantly lower in chronic tension type headache, both at the pericranial sites and over the Achilles tendon.” The deep pain of bone and periosteum has not been investigated systematically. The rationale for using periosteal sensitivity is justified by the fact that pain originating in the periosteum forms part and parcel of numerous musculoskeletal disorders.“,” Furthermore, stimulation of the periosteal nociceptors is used clinically to assess deep sensation during neurological examination.” Lastly, the examination of bony areas permits placement of the algometer on a well defined and circumscribed area, thus preventing the interference of technical artefacts arising from the movement of soft tissue that may occur with pain measurement over muscles.23 In other words, using bony areas for assessment of pain will improve the reliability of the examination, a need that has been stressed by other investigators.13 Quantification of the response of bony areas to pressure may provide a reliable dimension for comparing pain threshold and
DEEP PAIN PRESSURE ALGOMETRY, tolerance between various groups of pain sufferers. It may also assist in studying the effect of therapy on sensitivity to evoked pain. The purpose of this study was to define parameters of deep pressure pain measurements in healthy subjects, so as to provide a basis for comparison with future investigations of patients suffering from various pain syndromes. The following report presents the results of pressure algometry examinations carried out on five bony locations in healthy \ olunteers. using an electronic push-button algometer.
MATERIALS
AND
METHODS
Pressure algometry was applied in 24 healthy volunteers ( 14 men and 10 women. aged 20 to 40 years) after informed
consent and approval of the protocol by the Hospital Ethics Committee. None of the subjects suffered from any systemic disease or pain syndrome, and all were right-hand dominant. The instructlons for signalling onset of pain (threshold) and unacceptibility of pain (tolerance) were identical for all participants. In this study, the pressure algometer. which has been described previously. ” consisted of a commerciallv available force-displacement transducer.” with the following. easily constructed. modifications: ( I ) a round, teflon tip with an area of 025cm’ attached to one of the beam shafts of the transducer. and (2) an aluminum handle mounted on the transducer to facilitate continuous pressure on the selected anatomical point. The modified algometer is connected to an amplifier” that is plugged into a two-channel recorder’ equipped with a time marker linked to one channel (fig 1). ‘The marker is activated by the subject via a hand-held push
Vatine
527
button, thus eliminating the verbal subject-examiner delay, and affording instantaneous recording of the pain response signals. The force was applied to increase from 0 to 1Okg in IOsec and to produce a deflection of 5mm/kg on the other channel of the recorder. Recording speed was Smm/sec. This range of force increment proved optimal for the subjects, as well as a convenient rate of increase in force application for the examiner. At the sa.me time. it prevented undue prolongation of pressure with potential persistence of pain and tissue damage. Typically after only a short practice. the examiner becomes skilled In applying force increments at the controlled rate of 1kg/set. The visualization of the force signal on the recorder nol. only assists the examiner in attaining this skill, but also shows the constancy of the rise in pressure during each examination (fig 3). The osseus locations chosen for the pressure pain examinations were the mastoid processes and the external malleolus bilaterally, and the sternum measured at two adjacent points (7 and 9cm below the upper border on the midline), in order to avoid evaluation of pararneters from an immediately previously sensitized area. These two points were considered a single site of measurement. These sites lack overlying muscle, are covered by little t%t tissue. and constitute well circumscribed areas. The sites were examined following a fixed order: sternum, right mastoid. right external malleolus. left external malleolus, left mastoid, and sternum. One complete test required approximately ten minutes. The second test was performed one hour after the first one, using the same order of exammation. Although not a randomized method, it permitted variations in the time interval between the two measurements carried out at the sternum. Thus. the time interval between the two sternum
Fig I-The pressure algometry apparatus. A, pressure transducer: B, self-activated subject push button; C, two-channel recorder. Arch Phys Med Rehabil Vol74, May 1993
DEEP PAIN PRESSURE ALGOMETRY,
528
Vatine
Pressure pain threshold (PPT = onset of perception of pain) and tolerance to pain (PPtol = pain becoming unacceptable) were measured at each site of interest. The calculated difference between PPT and PPtol provided the range of sensitivity to pain (RSP). The results of the pressure algometry determinations are expressed in kilograms per 0.25 square centimeters. For comparison between sites, the mean values at the sternum were based only on the first examination values obtained in the two tests, in order to retain the same number of samples (48) in each group. The mean values for either sex group are based on four individual examinations, ie, two at each mastoid process, two at each malleolus and four at the sternum. Thus, the mean values at the mastoid process, malleolus, and sternum reflect 56 measurements for the 14 men and 40 measurements for the 10 women. For comparison of the right (dominant) side with the left side, only the values for the mastoid process and external malleolus were used. The values of the two tests for each lateralized site were pooled for all 24 subjects, that is, calculations for each of the parameters encompass the values of 48 examinations. Statistical
A A force applied at the sternum. Lower tracing: time marker. Arrows indicate markings of pain pressure threshold (FIT) and pain pressure tolerance (PPtol). Fig Z-Upper
tracing: pressure
recording from
pressure examinations during the same test was occupied by the measurements taken at the four other sites. whereas the interval between the second examination of the first test and the first examination of the second test was one hour. Table 1: Individual Pressure Algometry Values at the Sternum in 24 Volunteers (in kg/O.25 cm’) Age
Ses
Yl-f
31 52
F F F F F F F F F F M M M M M M M M M M M M M M
6
34 36 30 32 46 29 62 21 60 40 17 33 40 30 33 45 34 60 33 34 57 34
3.4 7.6 5.0 8.0 4.8 2.6 2.4 4.6 7.0 6.8 4.4 X.8 8.8 4.6 4.2 2.2 I.6 2.R 9.0 6.X X.0 3.6 7.0
Arch Phys Med Rehabil Vol74, May 1993
PPtol
RSP
7.4 7.2 8.6 5.8 10.0 5.0 IO.2 X.0 6.5
1.4 3.8 1.0 0.X 2.0 0.2 7.6 5.6 1.9 3.0 2.8 2.8
10.0
9.6 7.2 10.0
IO.0 11.0
8.8 2.6 4.3 4.X
I I.5 9.2 11.5 9.2 12.X
I.2 1.1 6.4
4.6 0.4 2.7 2.0 2.5 2.4 3.5 5.6 5.8
Analysis
Standard methods were used for descriptive statistics. For each measurement group (site, sex, side) the mean values and standard deviations were calculated. The significance of the difference between the means of two groups was tested by the randomization test for two independent samples. This test was chosen because it does not assume normal distributions or homogeneity of variance in the population involved. For all tests, p < 0.05 was considered significant.
RESULTS The values obtained at the sternum, mastoid processes and external malleoli showed large interindividual PPT and PPtol differences in both tests. Table 1, which presents the measurements at the sternum, exemplifies the wide range in parameter values. Table 2 lists the mean (t SD) values for PPT, PPtol, and RSP at all examined sites. The PPT values at the sternum were significantly higher than at the other sites tested, except for the right external malleolus. Table 2: Mean (LSD) Pressure Algometry Values According to Site (in kg/O.25 cm’)
Site
Pressure Pain Threshold I + + + f
2. I 1.9* 1.5* 2.1” 2.0*
Sternum Right mastoid Left mastoid Right malleolus Left malleolus
5.2 3.6 3.5 4.6 4.5
11represents comparison sites tested. * p < 0.00 I. ‘1’ < 0.01. *p i 0.5. ” p > 0.5 (nonsignilicant).
between the sternum
Pressure Pain Tolerance
Range of Sensitivity to Pain
7.9 + 1.X 2.6 7.6 2.3 2.3
i + ~ + _ t
1.61i 7 0” _. -J 0” _. 1.8”
values and each of the other
DEEP PAIN PRESSURE
PPtol values at the sternum were significantly higher than at all other sites. The RSP at the sternum was similar to that measured at the other sites. The mean pressure values obtained in the first test for each of the parameters at each site showed a persistent similarity with the respective values of the second test. In no instance were the intertest differences statistically significant (table 3). Table 4 presents the comparison between the pressure algometry values according to sex for all sites and parameters examined. The mean PTT \,alues for each of the examined points did not show significant gender differences. The mean PPtol values for the external malleolus in the women was, however, significantly lower (JI < 0.02). Mean RSP values were significantly lower in the women (mastoid p < 0.05. malleolus 11< 0.0 1) with the exception of the sternum, which showed similar values in both sexes. The mean values for the right (dominant) and left side did not differ significantly for either the mastoid process or the external malleolus (table 5).
DISCUSSION The high degree of intersubject difference in pain threshold and pain tolerance pressure algometry values determined at the same site noted in the present study is consistent with reports by other investigators,““-7.‘3.‘4 notwithstanding the rather small number of our subjects and their narrow age range. It is commonly accepted that the intersubject differences of sensitivity to pain arise in both the organic sensory dimension and the reaction component of the subject.” The differing somatic sensitivity to pain, the personality and emotional state of the subject. his interpretation of the instructions. or familiarity with the test after repeated examinations may all influence the results. This intersubject variability constitutes an unavoidable limitation of pressure algometry. However, the similar mean values recorded in this study at each of the sites for all three parameters in both first and second series of examinations showed the method to be reproducible and appropriate for comparison of groups. The unexpectedness of the discomfort elicited by the Table 3: Intertest Comparison of Pressure Algometry Values (mean t- SD) Obtained at the Examined Sites (in kg/O.25 cm*)
Test ILO.
Site - ____~~~
I 1 T 4 I
Stunurn
Right
mastold
3
Lcti mastoid Right
T 3
malleolus
I ct.1malleolu~ ~ -__.
~_.
11is nonsignlticant
T 3 ; 2
Pressure Pain Threshold
Pressure Pain Tolerance ___~
5.5 + 2.3 3.x t I.9 4.h -c 7. I 5.1 i 2.1 3.5 + I.‘)
8.1 i 2.1 7.5 t- 2.5 8.6 k I.7 8.0 f 2.h
3.7 3.4 3.5 4.5 4.7 4.7 4.x
tbr all intertest
L 2.0 + I.5 -t I.5 t ‘.O i 7.2 L? I.9 i 2.0
6.3 6.0 6.1 5.9 6.6
+ 2.5 + 2.3 -+ 2.7 t 2. I i 2.x 7.0 * 7.7 0.7 ?I 2.7 0.9 i 2.3
\aIues at any ofthe
Range af Sensitivity to Pain
3.0 t 2.1) 2.6 + 1.6 3.0 + 7.0 I.9 1.8 2.3 7.7
+ + * *
2.5 i ‘.I 2.3 3.5 2.1
-t -t L -t
examined sites.
1.3 I.5 I.6 2.1 1.7 I.9 1.6 3.3 2.1
ALGOMETRY,
Vatine
Table 4: Comparison of Pressure Algometry Values (mean f SD) Obtained at the Sites Examined According to Sex (in kg/O.25 cm2) __-____ I’emale (n z 101 .___
Male
Parameter
Site
5.2 + ” Sternum 3.3’17? hlastoid process hlalleolus 4.6 ? 2 I x.x + 3 5 Sternum Mastoid process (1.3 ? 3 7 7.4 L 2.7 Malleolus Sternum I.8 .I._‘i hlastoid process 7.‘) I I.Y ?q+lT Malleofus _.C _ -.______-._
I' f'T PPtol
RSP
Ahbre\iation:
(II = 14) _______~_
i3? :;
p Value
I.‘, ;_ 1:;
+
7 x 5 x 0 I1 2s 2 2 _.
f 1,s i 2.1 _(12.1 -1.’ +. I.5 16: I.1
NS. nonsignificant.
pain during the first examination has been mentioned by others as a possible cause for lowering the pain threshold.‘.“.’ ‘.I4which may explain the large interest variability. However. the similar values that were recorded at the sternum. irrespective whether examined as first (first examination of the first test) or as last point (second examination of the second test). seem to imply that familiarity with this technique is not a determinant in the response to applied force. The absence of overlying muscle and the scant fat tissue at the three osseus areas chosen in this study afforded a near direct response of bone to pressure stimuli with minimal interference. Contrary to the assumption that periostal sensitivity to pain would be similar at all locations studied. the pressure algometry values at the sternum proved signilicantly different from those recorded at the mastoid process and external malleolus in the two successive tests. The notable elevation of PPT and PPtol at the sternum and the high sensitivity to pain in the mastoid area could be ascribed to varying degrees of sensory innervation and the differing proportions of local nociceptive receptors. Similar persistent differences in response to pain stimuli between sites have been reported previously. especially with regard to muscle versus bone measurements.‘,“.‘5 These findings underscore once again that meaningful interpretation of reaction to pain is only possible if comparable anatomical sites are used for evaluation. For further elucidation of sensitivity to pain, the sternum is advised as the most suitable testing site. First of all, by virtue of the sternum’s low sensitivity. the influence ofthe Table 5: Comparison of Pressure Algometry Values (mean t SD) According to Side (in kg/O.25 cm2) -_-_ ___ Parameter
Site
Pressure pain threshold
Mastold procrs\ Malleolus Mastold process Malleolus Mastoid process Malleolus
Prcssurc pain tolerance Range ofscnsitivit! to pain 11is nonslgniiicant
Right (4% tests) 2.h t 4.6 k t.2 t r.Sk27 I’.0 * :.3+20
I x 2 I 2 5 I 5
._
I,eft (48 tests) 3.5 t
I.5 1.Y t 2.5 ? 2.5 + 1.x +- 1.x .~
4.4 + 6.0 6.X 2.5 2.3
for the three parameters in all inrtanccx
Arch Phys Med Rehabil Vol74, May 1993
DEEP PAIN PRESSURE ALGOMETRY, Vatine
530 variable time reaction component
is proportionally minimized in this bony area: secondly, the relatively large flat surface of the sternum permits stable contact between bone and algometer tip, thus enhancing the exactitude of the results. A number of investigators7,‘5*‘6,27reported a markedly higher sensitivity (lower PPT and PPtol) to pain in women. The present study did not reveal significant differences in PTT between the sexes (table 4). Our results demonstrate a statistically significant higher male PPtol for all sites examined. The fact that the difference in PPtol between the sexes was significant only at the malleolus, may be explained by the relative small number of subjects entered into the study. Some studies’5,‘8,‘9 found a relationship between lateral dominance and sensitivity to pain. No such dominance-related difference in response to the pressure stimuli was noted in our subjects (who were all right-handed), which concurs with results from other research.“22 These contradictory findings regarding laterality and pain response are probably due to selection of sites or the method of examination used. Although pressure algometry is a simple, noninvasive technique for the assessment of perception of force-induced pain, many equipment, examiner, and subject-related variables may interfere with the precision of the obtained measurements. To enhance reproducibility of the results, we used an algometer with a fixed area of pressure, controlled force, and application time, and with direct transference of the subject’s reaction. The serial measurements, analyzed independently for each of the bony areas studied, showed the technique to be reliable. Pressure algometry applied at nontender points may prove valuable for a better understanding of pain behavior in patients suffering from conditions characterized by severe pain, and, in turn, may contribute to their treatment. The technique and observations of the present study may be useful as a basis for comparing the responses to deep pain in various groups of pain patients. References
I. Fischer AA. Pressure tolerance 2. _3
4.
9.
over muscles and bones in normal subjects. Arch Phys Med Rehabil 1986;67:406-9. Tunks E. Crook J, Normann G, Kalaher S. Tender points in ftbromyalgesia. Pain I988:34: 1 1-9. Yunus MB, Kalyan-Raman UP, Kalyan-Raman K. Primary fibromyalgesia syndrome and myofacial pain syndrome: clinical features and muscle pathology. Arch Phys Med Rehabil 1988;69:45 1-4. Libman E. Observations on individual sensitiveness to pain with special reference to abdominal disorders. JAMA 1934:102:335-41. Pelner L. The determination of sensitivity to pain. J Lab Clin Med 1941;27:248-51. Keele KD. Pain sensitivity tests, the pressure algometer. Lancet 1954: 1:636-9. Merskey H. Spear FC. The reliability of the pressure algometer. Br J Sot Clin Psycho1 1964;3: 130-6. McCarthy DJ Jr. Gatter RA, Phelas P. A dolorimeter for quantification of articular tenderness. Arthritis Rheum 1965;8:55 1-9. Williams RC. Toward a set of reliable and valid measures for
Arch Phys Med Rehabil Vol74, May 1993
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a. b. C.
node1 FT 10, Grass Medical Instruments, 10 1 Old Colony Aveue, Quincy, MA 02 169. dodel 8805, Hewlett Packard Company, 4 Choke Cherry :oad, Rockville. MD 20850. /lode1 7702B. Hewlett Packard Company, 4 Choke Cherry Load, Rockville, MD 20850.