Authors:

Jo-Tong Chen, MDKao-Chi Chung, PhDChuen-Ru Hou, BSNTa-Shen Kuan, MDShu-Min Chen, MDChang-Zern Hong, MD

Affiliations:

From the Department of PhysicalMedicine and Rehabilitation, NationalCheng-Kung University, Tainan,Taiwan (JTC, TSK, SMC, CZH); andthe Institute of BiomedicalEngineering, National Cheng-KungUniversity, Tainan, Taiwan (KCC,CRH).

Disclosures:

Supported by the Taiwan NationalScience Council (NSC88-2314-B-006-101).

Correspondence:

All correspondence and requests forreprints should be addressed to Jo-Tong Chen, MD, Department ofPhysical Medicine and Rehabilitation,National Cheng-Kung UniversityHospital, 138 Sheng Li Road, Tainan,Taiwan.

0894-9115/01/8010-0729/0American Journal of PhysicalMedicine & RehabilitationCopyright 2001 by LippincottWilliams & Wilkins

Inhibitory Effect of Dry Needling onthe Spontaneous Electrical ActivityRecorded from Myofascial TriggerSpots of Rabbit Skeletal Muscle

ABSTRACTChen JT, Chung KC, Hou CR, Kuan CR, Chen SM, Hong CZ: Inhibitory effectof dry needling on the spontaneous electrical activity recorded from myofascialtrigger spots of rabbit skeletal muscle. Am J Phys Med Rehabil2000;80:729735.

Objective: Dry needling of myofascial trigger points can relieve myofascialpain if local twitch responses are elicited during needling. Spontaneous elec-trical activity (SEA) recorded from an active locus in a myofascial trigger pointregion has been used to assess the myofascial trigger point sensitivity. Thisstudy was to investigate the effect of dry needling on SEA.

Design: Nine adult New Zealand rabbits were studied. Dry needling withrapid insertion into multiple sites within the myofascial trigger spot region wasperformed to the biceps femoris muscle to elicit sufficient local twitch re-sponses. Very slow needle insertion with minimal local twitch response elici-tation was conducted to the other biceps femoris muscle for the control study.SEA was recorded from 15 different active loci of the myofascial trigger spotbefore and immediately after treatment for both sides. The raw data of 1-secSEA were rectified and integrated to calculate the average integrated value ofSEA.

Results: Seven of nine rabbits demonstrated significantly lower normalizedaverage integrated value of SEA in the treatment side compared with thecontrol side (P 0.05). The results of two-way analysis of variance show thatthe mean of the normalized average integrated value of SEA in the treatmentgroup (0.565 0.113) is significantly (P 0.05) lower than that of the control(0.983 0.121).

Conclusions: Dry needling of the myofascial trigger spot is effective in di-minishing SEA if local twitch responses are elicited. The local twitch responseelicitation, other than trauma effects of needling, seems to be the primaryinhibitory factor on SEA during dry needling.

Key Words: Myofascial Trigger Points, Myofascial Pain Syndrome, NeedleInjection, Abnormal Endplate Potentials, Local Twitch Response

October 2001 Effect of Dry Needling on Trigger Points 729

Research Article

Myofascial Pain

Myofascial trigger points (MTrP)are characteristic of myofascial painsyndrome, the most common musclepain disorder in clinical practice.1,2

MTrP is a hyperirritable spot in apalpable taut band that is firmer inconsistency than the adjacent musclefibers.3,4 When an MTrP is mechani-cally stimulated through snapping orneedling, local twitch responses(LTRs), brisk contraction of the tautband (but not the surrounding nor-mal muscle fibers), can be elicited.49

Clinically, MTrP injection has oftenbeen used as an effective and valuableprocedure to inactivate an activeMTrP and subsequently relieve thepain and tightness of the muscle in-volved in myofascial pain syndrome.During MTrP injection, as soon as theneedle penetrates to a sensitive site,an LTR usually can be elicited, espe-cially for rapid needling.6,7,10 Dryneedling of the MTrP has been re-ported to be as effective as local an-esthetic injection.6,7,1012 Effectiveoutcomes of MTrP injection or dryneedling have been associated withthe elicited LTRs.6,7,10 On the con-trary, little clinical effectiveness hasresulted from minimal LTR elicita-tion. Studies in both human and an-imal experiments have suggested thatimmediately after an effective injec-tion or dry needling, LTRs would besuppressed and no more LTRs couldbe elicited by further needling.6 Itseems that LTR is closely related tothe activity (or pain intensity) of anMTrP.

Research studies have been con-ducted to develop an animal modelfor addressing the issue of MTrP inhumans.1317 In the rabbit model weused, taut bands were palpable in theskeletal muscles. A hyperirritablespot in the taut band could also beidentified. When the rabbit wasawake, compression of this spot usu-ally caused responses in the animal asif it suffered pain or discomfort. Thissensitive spot was defined as a myo-fascial trigger spot (MTrS), similar to

human MTrP in many aspects. RabbitLTRs, similar to human LTRs, can beelicited when a mechanical stimula-tion is applied to the MTrS region. Ithas been reported that the LTR ismediated by means of a spinal reflexin both humans8 and rabbits.13,14

However, the exact mechanism ofLTR is still unclear. It is also un-known why it is important to elicitLTRs during MTrP injection to obtaina better treatment effect.

Electrophysiologic studiesshowed that spontaneous electricalactivity (SEA) can be recorded frommultiple active loci in an MTrP re-gion in humans18,19 or in an MTrSregion in rabbits.15,17 SEA consists ofcontinuous, noise-like action poten-tials (550 V, occasionally up to 80V) accompanied by intermittent,large-amplitude spikes (100600 V,biphasic, initially negative). Thiselectrical activity would disappear ifthe recording needle electrode wasadvanced or withdrawn as little as 1mm. The control needle electrode innearby muscle fibers of the taut bandshowed no SEA. Previous studieshave indicated that SEA can be re-corded more frequently in an MTrSregion than in a control site of rabbitskeletal muscles, and similar findingshave also been demonstrated in hu-man skeletal muscles.17

Simons has indicated that anSEA is an abnormal endplate poten-tial caused by excessive leakage ofacetylcholine (ACh).4 The spikes inSEA are propagated single-fiber mus-cle action potentials originating inthe immediate vicinity of the end-plate zone. The excessive ACh releasedepolarizes the postjunctional mem-brane, which may cause additionalCa2 release to aggravate the tautband formation through the mecha-nism of energy crisis.4

It has been demonstrated thatthe magnitude of SEA is significantlyincreased by laboratory stressors inboth healthy subjects20 and patientswith tension headaches21 or chronicmyofascial pain syndrome.19 Further-

more, the magnitude of SEA isclosely related to the pain intensity inpatients with chronic and recurrentmuscle pain associated withMTrPs.18,19 However, the interrela-tion of SEA, LTR, and MTrP injectionis still unknown.

Our hypothesis is that dry nee-dling of MTrP is useful in diminish-ing SEA, leading to effective pain re-lief of myofascial pain syndromepatients. The aim of this study was toapply electrophysiologic signal analy-sis in quantitatively characterizingthe change of SEA for dry needlingon MTrS, using a rabbit model.

METHODS

Animal Preparation. Nine adult NewZealand rabbits with body weightsranging from 8 to 10 pounds werestudied. All procedures used in thisstudy were approved by the Institu-tional Animal Care and Use Commit-tee of the National Cheng-Kung Uni-versity. Each animal was anesthetizedwith an intramuscular injection ofketamine 0.05 mg/kg of body weightprior to intravenous injections ofthiopentone sodium (0.01 g/ml). Bi-lateral biceps femoris muscles wereseparated from the underlying semi-membranosus muscles after the skinof the lateral thigh was incised.

Identification of MTrS. The bicepsfemoris muscle was palpated bygently rubbing (rolling) it betweenthe fingers to find taut bands. A tautband feels like a clearly delineatedrope of muscle fibers roughly 23mm or more in diameter. Snappingpalpation testing was applied on theband for LTRs elicited. The MTrS ofrabbit skeletal muscle was deter-mined from the location along theband with the most vigorous LTRs inthe snapping palpation testing.

Electrophysiologic Recordings ofSEA. For SEA recording in an MTrSregion, a monopolar electromyo-graphic needle electrode was initially

730 Chen et al. Am. J. Phys. Med. Rehabil. Vol. 80, No. 10

inserted into a taut band region andconnected to channel 1 of a 4-chan-nel Viking EMG System (Nicolet Bio-medical Inc., Madison, WI). The con-trol needle electrode was insertedinto the nearby normal muscle fibersand connected to channel 2. The ref-erence electrode common to bothchannels 1 and 2 and the groundelectrode were attached to the adja-cent subcutaneous tissue. The sensi-tivity of recording was set at 0.02 mVper division, and the sweeping speedof the screen was set at 10 msec perdivision.

Search for SEA. The active recordingneedle was advanced gently andslowly along the muscle fibers in theMTrS region. Each advance was of ashort distance (for only about 1 mm)because of the minute size of an ac-tive locus. Fifteen sets of SEA wererecorded from different active lociwithin the MTrS region (2 2 cm) ofbiceps femoris muscle before and im-mediately after rapid dry needling fortreatment and very slow needle in-serting for control.

Dry Needling to Elicit LTRs. In dryneedling treatment, repetitive andrapid needle inserting into multiplesites in the MTrS region was appliedto elicit sufficient LTRs. LTRs, whichare generally both palpable (feeling ofmuscle twitch) and visible, are recog-nized by firm finger palpation overthe MTrS region. The numbers ofLTR elicited during dry needlingwere recorded for comparison. Con-trol study was conducted on theother side by very slow needle inser-tion along the muscle fibers in theMTrS region for minimal LTRelicitation.

Signal Processing. Data collectionand analysis were done with a PC-586computer and DaqBook 100 (12 bits,16 channels, maximum samplingrate of 100 kHz) analog-to-digitalconverter (IOtech Inc., Cleveland,OH). The SEA signal was sampled at

20 kHz then detrended and filteredout with a 60-Hz notch filter by useof MATLAB 5.0 software (MathWorks,Inc., Natick, MA). The raw data of1-sec SEA were rectified and inte-grated to calculate the average inte-grated value for each SEA recording(AIV-SEA) (Fig. 1). The signal ofspikes was included because thespikes are considered to represent amore active SEA because they areusually found in an active MTrPrather than a latent one.18

Data Analysis. The AIV-SEA was usedas an index of the intensity of SEAand dependent variable for statisticalanalysis using SPSS/PC package(SPSS Inc., Chicago, IL).15 The AIV-SEA parameter was initially tested forheterogeneity between and withinrabbits and groups to validate its fea-sibility in the quantitative measure-ment of SEA. In each group, themean of AIV-SEA after needle injec-tion was normalized with the data

before injection. For each individualrabbit, t test was used to compare thenormalized AIV-SEA between treat-ment and control sides. Lumped datafrom all nine rabbits were further an-alyzed with two-way analysis of vari-ance for statistical significance be-tween treatment and control groups.A significance level of 0.05 was se-lected for this study.

RESULTS

Figure 2 shows a typical exampleof the SEA recordings from an MTrSregion of a rabbit before and imme-diately after dry needling of MTrS.The magnitude of raw SEA data areobviously suppressed after dry nee-dling. All the data of AIV-SEA re-corded from 15 different loci withinthe MTrS region in both treatmentand control sides of nine rabbits haveexhibited a normal distribution pat-tern consistently. In the treatmentgroup, the numbers of LTR elicitedduring rapid dry needling on ninerabbits are ranged from 22 to 37times with mean and standard devia-tion at 30.2 4.7 (median and modeequal to 30), whereas in the controlgroup, the numbers of LTRs elicitedduring very slow needle insertion areranged from 6 to 10 times, with meanand standard deviation at 8.4 1.4(median and mode equal to eight).The results of the t test demonstratethat the numbers of LTRs of the dryneedling group are significantlylarger than those of the controlgroup. The means of normalized AIV-SEA in the treatment group are lowerthan those in the control group forall nine rabbits; the results of the ttest on treatment effect comparisonindicate that seven out of nine rabbitshave a significantly lower normalizedAIV-SEA on the treatment side thanon the control side (P 0.05) (Fig.3). In the two-way analysis of vari-ance of treatment and rabbit factors,the statistical results with means andstandard deviations (Table 1) showthat the normalized AIV-SEA in the

Figure 1: Electrophysiologic signalprocessing of the spontaneous elec-trical activity (SEA).

October 2001 Effect of Dry Needling on Trigger Points 731

treatment group (0.565 0.114) issignificantly lower than that of thecontrol group (0.983 0.121; P 0.05).

DISCUSSION

Electrophysiologic studies of themotor endplate have shown thatthere is intermittent quantal releaseof ACh from the nerve terminals, re-sulting in the appearance of discreteminiature endplate potentials(MEPPs).22 There is evidence that the

discharges caused by spontaneous lo-cal excitation of individual motornerve endings or small, specializedmembrane areas that are concernedwith the release of ACh.23 Jones andcoworkers drew attention to the pres-ence of two types of spontaneouselectromyographic activity in normalmuscles at rest.24 They described twocomponents that are similar to SEApattern. The first is characterized byhigh-frequency negative monophasicdeflections of low amplitudes (520V). The second component consists

of a variable number of biphasic spikepotentials (100500 V). Similar po-tentials have been observed in the rat,guinea pig, cat, dog, rabbit, and mon-key.2427 In humans, these potentialsmay be observed in 510% of routineinsertions of the needle into normalmuscle and can be observed morefrequently in the region of the motorpoint.24 Buchthal and coworkers26

originally suggested that the firsttype of activity, also known as end-plate noise, corresponds to extracel-lularly recorded MEPPs emanatingfrom endplates located adjacent tothe needle electrode. The second typeof activity, referred to as endplatespikes, corresponds to single musclefiber action potentials postsynapti-cally activated by suprathresholdendplate noise. Wiederholt examinedrabbit endplate noise with histologic,electrophysiologic, and pharmaco-logic means. He concluded that po-tentials in endplate noise areMEPPs.27 The issue of whether theendplate noise (SEA) arises from nor-mal or abnormal endplates is criticaland questions conventional belief.Normal endplate potentials are occa-sional, discrete, short, and negativemonophasic potentials. Endplatenoise is the result of a 100- to 1000-fold increase in the rate of release ofACh.

Figure 2: Electromyographic recording of spontaneous electrical activity from the active locus of the myofascial triggerspot in the biceps femoris muscle of a rabbit before (left) and immediately after dry needling (right).

Figure 3: Means of the normalized averaged integrated value (AIV) of sponta-neous electrical activity (SEA) in 15 different loci in the treatment and thecontrol sides.

732 Chen et al. Am. J. Phys. Med. Rehabil. Vol. 80, No. 10

A newborn baby may have verylittle, if any, activated loci in the skel-etal muscle.4 As the motor systembecomes more and more active dur-ing the growing period, the musclesor other surrounding tissues are vul-nerable to stressful life events andabnormal muscle stress. As a conse-quence, spontaneous local excitationof individual motor nerve endings in-creases with age. Originally, thosescattered activated loci are not pain-ful, but later on, some of them mayaccumulate in a certain region andform a latent MTrP. Further mechan-ical stress or other aggravating fac-tors may cause a latent MTrP to be-come active. Latent MTrPs, whichoften cause tenderness and motordysfunction (stiffness and restrictedrange of motion), are far more com-mon than the active MTrPs thatcause spontaneous pain. Reports ofthe prevalence of latent MTrPs inhealthy young individuals are avail-able and indicate a high preva-lence.28,29 Similarly, we could searchthe SEA signal easily from the motorpoint area (latent MTrP) of bicepsfemoris muscles of adult New Zea-land rabbits, although variations inSEA magnitude and accumulationwere found.15,17

In this study, dry needling to anMTrS region could effectively sup-press SEA if LTRs were elicited. Isthere a possibility that the insertionof a needle at the endplate region,especially rapidly, may lead to greaterendplate discharges and thereby re-duce immediately available AChstores such that the SEA is reduced?It is also possible that sufficient me-chanical activation of endplates byneedle stimulation causes muscle fi-bers to discharge and thus to elicitLTR. It has been demonstrated thatLTRs in humans and animals are as-sociated with a transient burst ofEMG activity.8,9,13,14 The electromyo-graphic activity of LTRs almost dis-appeared after Lidocaine block ortransection of the innervating musclenerve. This activity disappeared tem-porarily after spinal cord transectionduring the spinal shock period butwas almost completely recovered af-ter the spinal shock stage. It was pro-posed that LTRs are mediatedthrough the nervous system and in-tegrated at the spinal cord level.8,13,14

Hong and Simons, based on recentstudies in humans and animals, haveproposed the multiple loci conceptand postulated that there are multi-ple MTrP loci in an MTrP region.3 An

MTrP locus consists of a sensitive lo-cus (the site from which an LTR canbe elicited by needle stimulation) andan active locus (the site from whichSEA can be recorded). The sensitivelocus may be sensitized nociceptivenerve fibers in the immediate vicinityof an active locus with dysfunctionalmotor endplates.3,16 The mechanicalstimulation of an MTrP could activatethe sensitive locus. When these po-tentials are propagated by means ofafferents to the spinal cord, they re-flexly cause corresponding motoneu-rons to fire and thus produce an LTR.However, the underlying mechanismfor the effectiveness of MTrP injec-tion resulted from LTR elicitation isstill unclear.

In an ongoing study conductedat our laboratory, the change of AIV-SEA after dry needling with time wasinvestigated using seven rabbits. TheAIV-SEA were recorded immediatelyafter the treatment procedure and ata half hour, 1 hr, 2 hr, and 4 hr afterthe treatment procedure. During the4-hr experimental period, the AIV-SEA recorded from the active locuswere constantly suppressed after dryneedling of the MTrS. The AIV-SEAdid not return to pretreatment levelsin the course of the experiment.Therefore, the inhibitory effect of dryneedling on SEA seems not to betransient.

One may speculate that the in-hibitory effect of dry needling on SEAmay be caused by the trauma effectsof needling, such as edema or hema-toma formation. The control study onthe other side of the same rabbit in-dicated that slow needle insertioninto the MTrS region for minimalLTR elicitation has not caused anyinhibitory effect on SEA. LTR elicita-tion is likely to be the key factorattributing to SEA suppression. Inour study, we never observed thatrapid needle movement caused moreedema or ecchymosis to the musclethan the slow needle movement inthe control study. This is also true inclinical practice on MTrP injection.6,7

TABLE 1Mean and SD of normalized average integrated value ofspontaneous electrical activity in two-way analysis ofvariance

RabbitDry Needling Side

(V)Control Side

(V)

1 0.688 0.274 0.883 0.6072 0.577 0.105a 0.987 0.3653 0.452 0.217a 0.995 0.3034 0.614 0.255a 1.040 0.3255 0.449 0.141a 0.751 0.3546 0.390 0.180a 0.995 0.4457 0.730 0.446 0.940 0.3758 0.581 0.369a 1.177 0.5579 0.606 0.273a 1.084 0.479

Mean SD 0.565 0.114a 0.983 0.121a Significant differences (P 0.05) between dry needling and control sides.

October 2001 Effect of Dry Needling on Trigger Points 733

Therefore, the trauma effect woundnot play any significant role for suchchanges.

Many researchers have docu-mented the similarity between acu-puncture and dry needling in treatingMTrP.6,7,10,12,30,31 According to thetheory of acupuncture, it has beenemphasized that Teh-Chi (gainingspirit) must be attained during acu-puncture to provide the therapeuticeffect.31 Teh-Chi has been describedin ancient Chinese medical literatureas a feeling coming from the needlejust like a fish biting to pull thefishing line. If there is no Teh-Chiresponse during acupuncture (it feelslike standing in the empty vicinity ofa long hall), little or no therapeuticeffect can be found. To a certain ex-tent, acupuncture is probably similarto MTrP injection, and the Teh-Chieffect is probably similar or related toeliciting LTRs. This correlation sug-gests that MTrP and acupuncturepoints for pain may represent thesame phenomenon and can be ex-plained in terms of the same under-lying neural mechanisms. The resultsof this study are consistent with clin-ical findings that LTRs must be elic-ited during MTrP injection to attainthe therapeutic effect.

This study provides evidence thatSEA can be inhibited by dry needlingthat elicits LTRs. The application ofAIV-SEA as an evaluation indexseems to be highly feasible in thequantitative measurement of SEA.However, the distances between therecording electrode and the endplatesthat profoundly influence MEPP am-plitudes were not accurately mea-sured, although we tried to positionthe needle tip to obtain maximal SEA.Furthermore, the recorded signalmay consist of endplate noises andspikes, motor unit potentials, andmovement artifacts. Fortunately,those factors influenced both experi-mental and control studies to thesame extent. Further studies to ad-dress these issues are needed to con-

firm our findings and to elucidate thepathogenesis of MTrPs.

CONCLUSIONS

Dry needling of MTrS was provento diminish the SEA if LTRs wereelicited. The LTR elicitation, otherthan trauma effects of needling,seems to be the primary inhibitoryfactor on SEA during dry needling.

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Book Review

The Psychobiology of the Hand, Edited by Kevin J. Connolly, Published 1999. Cambridge University Press, Sheffield,United Kingdom $69.95

This was part of a series Clinics in Developmental Medicine. Although the title was intriguing, the contentsdid not live up to the promise. For example, the first chapter was written by a hand surgeon but might havebeen more appropriately done by an anatomist. The tendon of the flexor carpiradialis was omitted from thecarpal tunnel and the long finger was called the MIDDLE finger; the human hand has five digits and a thumband four fingers, so there is a middle digit but no middle finger. The median nerve was said to contain all theroots from the brachialplexus (C5-T1). A chapter devoted to function of the nonhuman hand was excellent, aswere the eight chapters covering the developing hand of the infant and child and the last chapter, HandFunction in a Variety of Neurologic Disorders. A major disadvantage could be the misleading title, whichpromises much more than the book delivers. A more convincing and relevant title would be simply TheDeveloping Hand.

Book Rating: ***

Ernest W. Johnson, MD

Columbus, Ohio

October 2001 Effect of Dry Needling on Trigger Points 735