Inhibitory Effect of Dry Needling on the Spontaneous Electrical Activity Recorded from Myofascial Trigger Spots of Rabbit Skeletal Muscle.pdf

Authors:

Jo-Tong Chen, MD

Kao-Chi Chung, PhD

Chuen-Ru Hou, BSN

Ta-Shen Kuan, MD

Shu-Min Chen, MD

Chang-Zern Hong, MD

Myofascial Pain

Research Article

Afﬁliations:

From the Department of Physical

Medicine and Rehabilitation, National

Cheng-Kung University, Tainan,

Taiwan (JTC, TSK, SMC, CZH); and

the Institute of Biomedical

Engineering, National Cheng-Kung

University, Tainan, Taiwan (KCC,

CRH).

Inhibitory Effect of Dry Needling on

the Spontaneous Electrical Activity

Recorded from Myofascial Trigger

Spots of Rabbit Skeletal Muscle

Disclosures:

Supported by the Taiwan National

Science Council (NSC

88-2314-B-006-101).

Correspondence:

ABSTRACT

Chen JT, Chung KC, Hou CR, Kuan CR, Chen SM, Hong CZ: Inhibitory effect

of dry needling on the spontaneous electrical activity recorded from myofascial

trigger spots of rabbit skeletal muscle. Am J Phys Med Rehabil

2000;80:729 –735.

Objective: Dry needling of myofascial trigger points can relieve myofascial

pain if local twitch responses are elicited during needling. Spontaneous elec-

trical activity (SEA) recorded from an active locus in a myofascial trigger point

region has been used to assess the myofascial trigger point sensitivity. This

study was to investigate the effect of dry needling on SEA.

Design: Nine adult New Zealand rabbits were studied. Dry needling with

rapid insertion into multiple sites within the myofascial trigger spot region was

performed 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 spot

before and immediately after treatment for both sides. The raw data of 1-sec

SEA were rectiﬁed and integrated to calculate the average integrated value of

SEA.

Results: Seven of nine rabbits demonstrated signiﬁcantly lower normalized

average integrated value of SEA in the treatment side compared with the

control side ( P

All correspondence and requests for

reprints should be addressed to Jo-

Tong Chen, MD, Department of

Physical Medicine and Rehabilitation,

National Cheng-Kung University

Hospital, 138 Sheng Li Road, Tainan,

Taiwan.

0894-9115/01/8010-0729/0

American Journal of Physical

Medicine & Rehabilitation

Williams & Wilkins

0.05). The results of two-way analysis of variance show that

the mean of the normalized average integrated value of SEA in the treatment

group (0.565

0.113) is signiﬁcantly ( P

0.05) lower than that of the control

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 response

elicitation, other than trauma effects of needling, seems to be the primary

inhibitory factor on SEA during dry needling.

Key Words: Myofascial Trigger Points, Myofascial Pain Syndrome, Needle

Injection, Abnormal Endplate Potentials, Local Twitch Response

October 2001

Effect of Dry Needling on Trigger Points

729

(0.983

M yofascial trigger points (MTrP)

are characteristic of myofascial pain

syndrome, the most common muscle

pain disorder in clinical practice. 1,2

MTrP is a hyperirritable spot in a

palpable taut band that is ﬁrmer in

consistency than the adjacent muscle

ﬁbers. 3,4 When an MTrP is mechani-

cally stimulated through snapping or

needling, local twitch responses

(LTRs), brisk contraction of the taut

band (but not the surrounding nor-

mal muscle ﬁbers), can be elicited. 4–9

Clinically, MTrP injection has often

been used as an effective and valuable

procedure to inactivate an active

MTrP and subsequently relieve the

pain and tightness of the muscle in-

volved in myofascial pain syndrome.

During MTrP injection, as soon as the

needle penetrates to a sensitive site,

an LTR usually can be elicited, espe-

cially for rapid needling. 6,7,10 Dry

needling of the MTrP has been re-

ported to be as effective as local an-

esthetic injection. 6,7,10 –12 Effective

outcomes of MTrP injection or dry

needling have been associated with

the elicited LTRs. 6,7,10 On the con-

trary, little clinical effectiveness has

resulted from minimal LTR elicita-

tion. Studies in both human and an-

imal experiments have suggested that

immediately after an effective injec-

tion or dry needling, LTRs would be

suppressed and no more LTRs could

be elicited by further needling. 6 It

seems that LTR is closely related to

the activity (or pain intensity) of an

MTrP.

Research studies have been con-

ducted to develop an animal model

for addressing the issue of MTrP in

humans. 13–17 In the rabbit model we

used, taut bands were palpable in the

skeletal muscles. A hyperirritable

spot in the taut band could also be

identiﬁed. When the rabbit was

awake, compression of this spot usu-

ally caused responses in the animal as

if it suffered pain or discomfort. This

sensitive spot was deﬁned as a myo-

fascial trigger spot (MTrS), similar to

human MTrP in many aspects. Rabbit

LTRs, similar to human LTRs, can be

elicited when a mechanical stimula-

tion is applied to the MTrS region. It

has been reported that the LTR is

mediated by means of a spinal reﬂex

in both humans 8 and rabbits. 13,14

However, the exact mechanism of

LTR is still unclear. It is also un-

known why it is important to elicit

LTRs during MTrP injection to obtain

a better treatment effect.

Electrophysiologic studies

showed that spontaneous electrical

activity (SEA) can be recorded from

multiple active loci in an MTrP re-

gion in humans 18,19 or in an MTrS

region in rabbits. 15,17 SEA consists of

continuous, noise-like action poten-

tials (5–50

more, the magnitude of SEA is

closely related to the pain intensity in

patients with chronic and recurrent

muscle pain associated with

MTrPs. 18,19 However, the interrela-

tion of SEA, LTR, and MTrP injection

is 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 syndrome

patients. The aim of this study was to

apply electrophysiologic signal analy-

sis in quantitatively characterizing

the change of SEA for dry needling

on MTrS, using a rabbit model.

METHODS

V, occasionally up to 80

Animal Preparation. Nine adult New

Zealand rabbits with body weights

ranging from 8 to 10 pounds were

studied. All procedures used in this

study were approved by the Institu-

tional Animal Care and Use Commit-

tee of the National Cheng-Kung Uni-

versity. Each animal was anesthetized

with an intramuscular injection of

ketamine 0.05 mg/kg of body weight

prior to intravenous injections of

thiopentone sodium (0.01 g/ml). Bi-

lateral biceps femoris muscles were

separated from the underlying semi-

membranosus muscles after the skin

of the lateral thigh was incised.

biphasic, initially negative). This

electrical activity would disappear if

the recording needle electrode was

advanced or withdrawn as little as 1

mm. The control needle electrode in

nearby muscle ﬁbers of the taut band

showed no SEA. Previous studies

have indicated that SEA can be re-

corded more frequently in an MTrS

region than in a control site of rabbit

skeletal muscles, and similar ﬁndings

have also been demonstrated in hu-

man skeletal muscles. 17

Simons has indicated that an

SEA is an abnormal endplate poten-

tial caused by excessive leakage of

acetylcholine (ACh). 4 The spikes in

SEA are propagated single-ﬁber mus-

cle action potentials originating in

the immediate vicinity of the end-

plate zone. The excessive ACh release

depolarizes the postjunctional mem-

brane, which may cause additional

Ca 2 release to aggravate the taut

band formation through the mecha-

nism of energy crisis. 4

It has been demonstrated that

the magnitude of SEA is signiﬁcantly

increased by laboratory stressors in

both healthy subjects 20 and patients

with tension headaches 21 or chronic

myofascial pain syndrome. 19 Further-

Identiﬁcation of MTrS. The biceps

femoris muscle was palpated by

gently rubbing (rolling) it between

the ﬁngers to ﬁnd taut bands. A taut

band feels like a clearly delineated

“rope” of muscle ﬁbers roughly 2–3

mm or more in diameter. Snapping

palpation testing was applied on the

band for LTRs elicited. The MTrS of

rabbit skeletal muscle was deter-

mined from the location along the

band with the most vigorous LTRs in

the snapping palpation testing.

Electrophysiologic Recordings of

SEA. For SEA recording in an MTrS

region, a monopolar electromyo-

graphic needle electrode was initially

730

Chen et al.

Am. J. Phys. Med. Rehabil.

●

Vol. 80, No. 10

V) accompanied by intermittent,

large-amplitude spikes (100 – 600

inserted into a taut band region and

connected to channel 1 of a 4-chan-

nel Viking EMG System (Nicolet Bio-

medical Inc., Madison, WI). The con-

trol needle electrode was inserted

into the nearby normal muscle ﬁbers

and connected to channel 2. The ref-

erence electrode common to both

channels 1 and 2 and the ground

electrode were attached to the adja-

cent subcutaneous tissue. The sensi-

tivity of recording was set at 0.02 mV

per division, and the sweeping speed

of the screen was set at 10 msec per

division.

20 kHz then detrended and ﬁltered

out with a 60-Hz notch ﬁlter by use

of MATLAB 5.0 software (MathWorks,

Inc., Natick, MA). The raw data of

1-sec SEA were rectiﬁed and inte-

grated to calculate the average inte-

grated value for each SEA recording

(AIV-SEA) (Fig. 1). The signal of

spikes was included because the

spikes are considered to represent a

more active SEA because they are

usually found in an active MTrP

rather than a latent one. 18

before injection. For each individual

rabbit, t test was used to compare the

normalized AIV-SEA between treat-

ment and control sides. Lumped data

from 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

Data Analysis. The AIV-SEA was used

as an index of the intensity of SEA

and dependent variable for statistical

analysis using SPSS/PC package

(SPSS Inc., Chicago, IL). 15 The AIV-

SEA parameter was initially tested for

heterogeneity between and within

rabbits and groups to validate its fea-

sibility in the quantitative measure-

ment of SEA. In each group, the

mean of AIV-SEA after needle injec-

tion was normalized with the data

Figure 2 shows a typical example

of the SEA recordings from an MTrS

region of a rabbit before and imme-

diately after dry needling of MTrS.

The magnitude of raw SEA data are

obviously suppressed after dry nee-

dling. All the data of AIV-SEA re-

corded from 15 different loci within

the MTrS region in both treatment

and control sides of nine rabbits have

exhibited a normal distribution pat-

tern consistently. In the treatment

group, the numbers of LTR elicited

during rapid dry needling on nine

rabbits are ranged from 22 to 37

times with mean and standard devia-

tion at 30.2

Search for SEA. The active recording

needle was advanced gently and

slowly along the muscle ﬁbers in the

MTrS region. Each advance was of a

short distance (for only about 1 mm)

because of the minute size of an ac-

tive locus. Fifteen sets of SEA were

recorded from different active loci

within the MTrS region (2

4.7 (median and mode

equal to 30), whereas in the control

group, the numbers of LTRs elicited

during very slow needle insertion are

ranged from 6 to 10 times, with mean

and standard deviation at 8.4

Dry Needling to Elicit LTRs. In dry

needling treatment, repetitive and

rapid needle inserting into multiple

sites in the MTrS region was applied

to elicit sufﬁcient LTRs. LTRs, which

are generally both palpable (feeling of

muscle twitch) and visible, are recog-

nized by ﬁrm ﬁnger palpation over

the MTrS region. The numbers of

LTR elicited during dry needling

were recorded for comparison. Con-

trol study was conducted on the

other side by very slow needle inser-

tion along the muscle ﬁbers in the

MTrS region for minimal LTR

elicitation.

1.4

(median and mode equal to eight).

The results of the t test demonstrate

that the numbers of LTRs of the dry

needling group are signiﬁcantly

larger than those of the control

group. The means of normalized AIV-

SEA in the treatment group are lower

than those in the control group for

all nine rabbits; the results of the t

test on treatment effect comparison

indicate that seven out of nine rabbits

have a signiﬁcantly lower normalized

AIV-SEA on the treatment side than

on the control side ( P

Signal Processing. Data collection

and analysis were done with a PC-586

computer and DaqBook 100 (12 bits,

16 channels, maximum sampling

rate of 100 kHz) analog-to-digital

converter (IOtech Inc., Cleveland,

OH). The SEA signal was sampled at

0.05) (Fig.

3). In the two-way analysis of vari-

ance of treatment and rabbit factors,

the statistical results with means and

standard deviations (Table 1) show

that the normalized AIV-SEA in the

Figure 1: Electrophysiologic signal

processing of the spontaneous elec-

trical activity ( SEA ).

October 2001

Effect of Dry Needling on Trigger Points

731

2cm)of

biceps femoris muscle before and im-

mediately after rapid dry needling for

treatment and very slow needle in-

serting for control.

Figure 2: Electromyographic recording of spontaneous electrical activity from the active locus of the myofascial trigger

spot in the biceps femoris muscle of a rabbit before ( left ) and immediately after dry needling ( right ).

0.114) is

signiﬁcantly lower than that of the

control group (0.983

discharges caused by spontaneous lo-

cal excitation of individual motor

nerve endings or small, specialized

membrane areas that are concerned

with the release of ACh. 23 Jones and

coworkers drew attention to the pres-

ence of two types of spontaneous

electromyographic activity in normal

muscles at rest. 24 They described two

components that are similar to SEA

pattern. The ﬁrst is characterized by

high-frequency negative monophasic

deﬂections of low amplitudes (5–20

of a variable number of biphasic spike

potentials (100 –500

V). Similar po-

tentials have been observed in the rat,

guinea pig, cat, dog, rabbit, and mon-

key. 24 –27 In humans, these potentials

may be observed in 5–10% of routine

insertions of the needle into normal

muscle and can be observed more

frequently in the region of the motor

point. 24 Buchthal and coworkers 26

originally suggested that the ﬁrst

type of activity, also known as end-

plate noise, corresponds to extracel-

lularly recorded MEPPs emanating

from endplates located adjacent to

the needle electrode. The second type

of activity, referred to as endplate

spikes, corresponds to single muscle

ﬁber action potentials postsynapti-

cally activated by suprathreshold

endplate noise. Wiederholt examined

rabbit endplate noise with histologic,

electrophysiologic, and pharmaco-

logic means. He concluded that po-

tentials in endplate noise are

MEPPs. 27 The issue of whether the

endplate noise (SEA) arises from nor-

mal or abnormal endplates is critical

and questions conventional belief.

Normal endplate potentials are occa-

sional, discrete, short, and negative

monophasic potentials. Endplate

noise is the result of a 100- to 1000-

fold increase in the rate of release of

ACh.

0.121; P

0.05).

DISCUSSION

Electrophysiologic studies of the

motor endplate have shown that

there is intermittent quantal release

of ACh from the nerve terminals, re-

sulting in the appearance of discrete

miniature endplate potentials

(MEPPs). 22 There is evidence that the

V). The second component consists

Figure 3: Means of the normalized averaged integrated value ( AIV ) of sponta-

neous electrical activity ( SEA ) in 15 different loci in the treatment and the

control sides.

732

Chen et al.

Am. J. Phys. Med. Rehabil.

●

Vol. 80, No. 10

treatment group (0.565

TABLE 1

Mean and SD of normalized average integrated value of

spontaneous electrical activity in two-way analysis of

variance

MTrP locus consists of a sensitive lo-

cus (the site from which an LTR can

be elicited by needle stimulation) and

an active locus (the site from which

SEA can be recorded). The sensitive

locus may be sensitized nociceptive

nerve ﬁbers in the immediate vicinity

of an active locus with dysfunctional

motor endplates. 3,16 The mechanical

stimulation of an MTrP could activate

the sensitive locus. When these po-

tentials are propagated by means of

afferents to the spinal cord, they re-

ﬂexly cause corresponding motoneu-

rons to ﬁre and thus produce an LTR.

However, the underlying mechanism

for the effectiveness of MTrP injec-

tion resulted from LTR elicitation is

still unclear.

In an ongoing study conducted

at our laboratory, the change of AIV-

SEA after dry needling with time was

investigated using seven rabbits. The

AIV-SEA were recorded immediately

after the treatment procedure and at

a half hour, 1 hr, 2 hr, and 4 hr after

the treatment procedure. During the

4-hr experimental period, the AIV-

SEA recorded from the active locus

were constantly suppressed after dry

needling of the MTrS. The AIV-SEA

did not return to pretreatment levels

in the course of the experiment.

Therefore, the inhibitory effect of dry

needling on SEA seems not to be

transient.

One may speculate that the in-

hibitory effect of dry needling on SEA

may be caused by the trauma effects

of needling, such as edema or hema-

toma formation. The control study on

the other side of the same rabbit in-

dicated that slow needle insertion

into the MTrS region for minimal

LTR elicitation has not caused any

inhibitory effect on SEA. LTR elicita-

tion is likely to be the key factor

attributing to SEA suppression. In

our study, we never observed that

rapid needle movement caused more

edema or ecchymosis to the muscle

than the slow needle movement in

the control study. This is also true in

clinical practice on MTrP injection. 6,7

Rabbit

Dry Needling Side

(

Control Side

(

0.688

0.274

0.883

0.607

0.577

0.105 a

0.987

0.365

0.452

0.217 a

0.995

0.303

0.614

0.255 a

1.040

0.325

0.449

0.141 a

0.751

0.354

0.390

0.180 a

0.995

0.445

0.730

0.446

0.940

0.375

0.581

0.369 a

1.177

0.557

0.606

0.273 a

1.084

0.479

Mean

0.565

0.114 a

0.983

0.121

Signiﬁcant differences ( P

0.05) between dry needling and control sides.

A newborn baby may have very

little, if any, activated loci in the skel-

etal muscle. 4 As the motor system

becomes more and more active dur-

ing the growing period, the muscles

or other surrounding tissues are vul-

nerable to stressful life events and

abnormal muscle stress. As a conse-

quence, spontaneous local excitation

of individual motor nerve endings in-

creases with age. Originally, those

scattered activated loci are not pain-

ful, but later on, some of them may

accumulate in a certain region and

form a latent MTrP. Further mechan-

ical stress or other aggravating fac-

tors may cause a latent MTrP to be-

come active. Latent MTrPs, which

often cause tenderness and motor

dysfunction (stiffness and restricted

range of motion), are far more com-

mon than the active MTrPs that

cause spontaneous pain. Reports of

the prevalence of latent MTrPs in

healthy young individuals are avail-

able and indicate a high preva-

lence. 28,29 Similarly, we could search

the SEA signal easily from the motor

point area (latent MTrP) of biceps

femoris muscles of adult New Zea-

land rabbits, although variations in

SEA magnitude and accumulation

were found. 15,17

In this study, dry needling to an

MTrS region could effectively sup-

press SEA if LTRs were elicited. Is

there a possibility that the insertion

of a needle at the endplate region,

especially rapidly, may lead to greater

endplate discharges and thereby re-

duce immediately available ACh

stores such that the SEA is reduced?

It is also possible that sufﬁcient me-

chanical activation of endplates by

needle stimulation causes muscle ﬁ-

bers to discharge and thus to elicit

LTR. It has been demonstrated that

LTRs in humans and animals are as-

sociated with a transient burst of

EMG activity. 8,9,13,14 The electromyo-

graphic activity of LTRs almost dis-

appeared after Lidocaine block or

transection of the innervating muscle

nerve. This activity disappeared tem-

porarily after spinal cord transection

during the spinal shock period but

was almost completely recovered af-

ter the spinal shock stage. It was pro-

posed that LTRs are mediated

through the nervous system and in-

tegrated at the spinal cord level. 8,13,14

Hong and Simons, based on recent

studies in humans and animals, have

proposed the multiple loci concept

and postulated that there are multi-

ple MTrP loci in an MTrP region. 3 An

October 2001

Effect of Dry Needling on Trigger Points

733

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