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Archives of Physical Medicine and Rehabilitation
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Archives of Physical Medicine and Rehabilitation 2013;94:2146-50
ORIGINAL ARTICLE
Quantification of Dry Needling and Posture Effects on
Myofascial Trigger Points Using Ultrasound Shear-Wave
Elastography
Ruth M. Maher, PT, PhD, DPT, WCS, BCB-PMD, CEAS,a,b Dawn M. Hayes, PT, PhD, GCS,a
Minoru Shinohara, PhD, FACSMc
From the aDepartment of Physical Therapy, University of North Georgia, Dahlonega, GA; bUniversity College Dublin, School of Public Health,
Physiotherapy and Population Science, Dublin, Ireland; and cSchool of Applied Physiology, Georgia Institute of Technology, Atlanta, GA.
Current affiliation for Maher, Division of Physical Therapy, Shenandoah University, Winchester, VA.
Abstract
Objectives: To determine (1) whether the shear modulus in upper trapezius muscle myofascial trigger points (MTrPs) reduces acutely after dry
needling (DN), and (2) whether a change in posture from sitting to prone affects the shear modulus.
Design: Ultrasound images were acquired in B mode with a linear transducer oriented in the transverse plane, followed by performance of shearwave elastography (SWE) before and after DN and while sitting and prone.
Setting: University.
Participants: Women (NZ7; mean age Æ SD, 46Æ17y) with palpable MTrPs were recruited.
Intervention: All participants were dry needled in the prone position using solid filament needles that were inserted and manipulated inside the
MTrPs. SWE was performed before and after DN in the sitting and prone positions.
Main Outcome Measure: MTrPs were evaluated by shear modulus using SWE.
Results: Palpable reductions in stiffness were noted after DN and in the prone position. These changes were apparent in the shear modulus map
obtained with ultrasound SWE. With significant main effects, the shear modulus reduced from before to after DN (P<.01) and from the sitting to
the prone position (P<.05). No significant interaction effect between time and posture was observed.
Conclusions: The shear modulus measured with ultrasound SWE reduced after DN and in the prone position compared with sitting, in agreement
with reductions in palpable stiffness. These findings suggest that DN and posture have significant effects on the shear modulus of MTrPs, and that
shear modulus measurement with ultrasound SWE may be sensitive enough to detect these effects.
Archives of Physical Medicine and Rehabilitation 2013;94:2146-50
ª 2013 by the American Congress of Rehabilitation Medicine
From 1996 to 2006, U.S. residents more than tripled their
spending on prescription analgesics, from $4.2 to $13.2 billion.1
Since myofascial pain has a lifetime prevalence of 85% many
chronic pain disorders and syndromes of the musculoskeletal
system can be explained by the presence of localized, hyperirritable nodules in taut bands of skeletal muscle called myofascial
trigger points (MTrPs).2 These trigger points are tender on
palpation and cause pain, restricted range of motion, and
substantial motor dysfunction. The etiology of MTrPs is suggested
to be due to motor endplate dysfunction.2,3
No commercial party having a direct financial interest in the results of the research supporting
this article has conferred or will confer a benefit on the authors or on any organization with which
the authors are associated.
Dry needling is a technique used by a variety of clinicians in the
treatment of myofascial pain and motor dysfunction. A fine-gauge,
solid filament needle is inserted into discrete focal points of taut
bands within muscle and manipulated until local twitch responses
(LTRs) are elicited. The LTR is an involuntary spinal reflex
contraction of muscle fibers within a taut band and occurs during
needling of a taut band. This LTR elicited by dry needling is
associated with pain relief and a palpable reduction of muscle
stiffness.4 Despite the clinical efficacy of dry needling for alleviating the symptoms of MTrPs, objective quantification of the
severity of MTrPs in terms of muscle stiffness has not been possible.
The literature has shown that 2- and 3-dimensional ultrasound
imaging can be used for visualizing MTrPs and their associated
0003-9993/13/$36 - see front matter ª 2013 by the American Congress of Rehabilitation Medicine
http://dx.doi.org/10.1016/j.apmr.2013.04.021
Quantification of stiffness in myofascial trigger points
characteristics.5-10 Recently developed ultrasound shear-wave
imaging technology measures the shear-wave propagation
through soft tissues, thereby allowing for the objective quantification of the soft tissue stiffness in real time by means of the shear
modulus (in kilopascals). It would be useful if this technology
could provide a means for quantifying the muscle stiffness associated with MTrPs. Although this technology has been applied to
healthy human skeletal muscles,11,12 the applicability of the
technology to MTrPs and its treatment with dry needling is
unknown. Hence, we performed a preliminary study to provide
insights into the applicability of the ultrasound shear-wave
imaging technology in assessing the efficacy of dry needling on
muscle stiffness that is associated with MTrPs.
We expected that the shear modulus in the trapezius muscle
would be reduced acutely as a result of dry needling. In clinical
practice, the upper trapezius muscle is palpated with the patient in
the sitting, supine, or prone position. Since neuromuscular excitability is reduced in the supine position compared with the sitting
position,13 we also expected that the shear modulus in the trapezius muscle would be reduced with a change in posture from the
sitting to the prone position.
The primary and secondary objectives of this preliminary study
were as follows: (1) to compare the shear modulus of the upper
trapezius muscle with MTrPs before and after dry needling, and
(2) to compare the shear modulus of the upper trapezius muscle
between the prone and sitting positions, using ultrasound shearwave elastography.
Methods
Study population
Seven women (mean age Æ SD, 46Æ17.3y) who had palpable
MTrPs in their upper trapezius muscle were recruited. Subjects
completed a prescreening health history questionnaire and were
required to present with a palpable taut band that elicited pain and
the jump sign on palpation in the upper trapezius. Exclusion
criteria included a history of cervical radiculopathy, myelopathy,
muscular pain caused by fibromyalgia, trigger point injections in
the past 6 months, medications that affect muscle function, or
surgery to the neck or shoulder. Palpation was in the central region
of the upper trapezius muscle within 6cm of the muscular midline
(approximately midway between the cervical vertebrae and the
acromion process).8 In those who had bilateral trigger points, the
one that exhibited the most acute pain and jump sign was chosen
as the experimental site. The location of the trigger point was
marked on the skin. The University of North Georgia Institutional
Review Board approved this study, and each subject provided
written informed consent to participate.
Ultrasound imaging with shear-wave elastography
Ultrasound images were acquired in B mode using an ultrasound
system (Aixplorer version 4.0a) with a 4- to 15-MHz linear array
transducer.a The transducer was oriented in the transverse plane
List of abbreviations:
ANOVA analysis of variance
LTR local twitch response
MTrPs myofascial trigger points
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2147
over the region of interest on the upper trapezius muscle, and the
transducer was manipulated until the muscle fibers appeared
parallel. The boundaries of the transducer were then marked on
the skin to standardize the transducer position. Once a clear image
was acquired in B mode, supersonic shear imaging mode was used
to obtain the shear modulus map of the muscle for the region of
interest. Three elastography images were acquired in 5 seconds
before and immediately after dry needling in 2 subject postures:
(1) while subjects sat upright in a high backed chair, shoulders
relaxed with arms supported by armrests; and (2) in the prone
position with arms resting alongside their trunk. From each elastography image, the spatial average of the shear modulus (kPa) in
an 8-mm circular area was determined, and the values were
averaged across 3 measurements in each condition.
Dry needling
All subjects were dry needled in the prone position using a slowvelocity technique. A solid filament needle with guide tubeb
(0.2Â50mm) was inserted into the trigger point in the upper
trapezius muscle. The needle was manipulated up and down
(sweeps) inside the trigger point 10 times in an effort to standardize the dry needling protocol. Several LTRs were elicited.
Statistical analysis
The dependent variable was the shear modulus of the upper
trapezius muscle. The effects of time (before and after dry
needling) and posture (sitting and prone) were analyzed using
a 2-way repeated analysis of variance (ANOVA). An alpha value
less than .05 was considered significant. Mean data are presented.
Results
Palpable reductions in stiffness were noted after dry needling and
in the prone position. The reduction in stiffness resulting from dry
needling and the difference between postures were apparent in the
shear modulus map obtained with ultrasound elastography (fig 1).
When data in individual subjects were examined (table 1),
reductions in the shear modulus resulting from dry needling were
observed in all 7 subjects in both the sitting and prone positions.
By changing the posture from the sitting to prone position, the
shear modulus decreased in 5 of 7 subjects both before and after
dry needling. The amount of decrease resulting from the posture
change ranged from .29 to 9.82kPa, whereas the amount of
increase ranged from .16-1.35kPa. ANOVA found significant main
effects of time (P<.01) and posture (P<.05) on the shear modulus
(fig 2). The effect of time demonstrated a 29.5% reduction in the
shear modulus after dry needling, and the effect of posture
demonstrated a 21% reduction in the shear modulus from the
sitting to the prone position, on average (fig 3). A significant
interaction effect between time and posture was not observed.
Discussion
The new findings of the preliminary study are that the shear
modulus of the upper trapezius muscle with MTrPs was significantly reduced after dry needling and in the prone position, in
agreement with reductions in palpable stiffness. These findings
support that shear-wave elastography could quantitatively detect
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R.M. Maher et al
Fig 1 An example of a change in shear modulus in the upper
trapezius muscle resulting from dry needling and posture. Color-coded
representation in the presence of a palpable MTrP in the upper
trapezius muscle in the sitting position before (A) and after dry
needling (B) and in the prone position before (C) and after dry
needling (D). The color-coded scale was identical across images.
changes in stiffness in the form of shear modulus before and after
dry needling in the upper trapezius with MTrPs and with a change
in position from sitting to prone. These preliminary findings
provide a proof of concept for supporting that the technology
would be beneficial in that it can assess the morphology associated
with MTrPs, validate palpation as a means of diagnosing MTrPs,
and more importantly assess the effects of interventions such as
dry needling on these trigger points.
There is general agreement that any kind of muscle overuse or
direct trauma to the muscle can lead to the development of MTrPs;
however, the etiology and pathophysiology associated with MTrPs
are currently being studied but remain unclear.14 The proposed
etiology regarding MTrPs is that motor endplates of neurons
terminating at the muscle fibers of MTrPs have abnormal activity,
and that sustained sarcomere contracture leads to increased local
metabolic demand, compressed capillary circulation, and
increased metabolic by-products.2,3,15-22 In recent studies21,22 that
assessed the “biochemical milieu” or biochemical composition
associated with trigger points in the upper trapezius, elevated
levels of histochemicals, such as inflammatory mediators, proinflammatory cytokines, catecholamines, and neuropeptides, and
more acidic pH levels associated with chronic pain and inflammation were found in active MTrPs compared with normal muscle
tissue. Eliciting the LTR with dry needling reduced the presence
of these substances within the MTrPs, and the reductions were
associated with a decrease in pain and palpable stiffness.21 The
Fig 2 Effect of dry needling and posture on shear modulus of the
upper trapezius muscle. Main effects of dry needling (time) and
posture (position) are presented. **P<.01 vs Pre; *P<.05 vs Sitting.
LTR is an involuntary spinal reflex that results from mechanical
stimulation of the MTrP. It is visible and palpable, and thought to
occur in response to altered sensory spinal processing resulting
from sensitized peripheral mechanical nociceptors.4,10 This event
is associated with pain relief and a reduction of stiffness that is
palpable and observable on ultrasound imaging.21 The LTR is
therefore considered an objective sign of the presence of an MTrP.
Hence, the presence of MTrPs and the reduction in palpable
stiffness after dry needling are supported by the literature.
The novelty and significance of the present study is the
objective quantification of the stiffness reduction using ultrasound
shear-wave elastography. Palpation, pressure algometry, and
subjective pain reports are commonly used to diagnose and assess
outcomes associated with MTrPs. However, only moderate
evidence for the reproducibility of trigger point palpation of the
trapezius for local tenderness exists.23 The absence of objective
and reliable visual inspection of MTrPs has affected the willingness of the medical community to accept their existence and
affected the ability of clinicians to accurately assess treatment
outcomes.14 Several handheld devices have described viscoelasticity based on tissue indentation induced by manual compression
and static elastography using ultrasound imaging. However,
accurate quantification of stiffness cannot be made using these
Table 1 Shear modulus (kPa) of individual subjects for each
testing condition: time (before and after dry needling) and position (sitting and prone)
Sitting
Prone
Subject
Before
After
Before
After
1
2
3
4
5
6
7
Mean
11.29
9.62
15.72
12.28
10.66
18.46
16.89
13.56
8.87
9.60
12.32
8.83
8.81
9.16
6.18
9.11
7.94
10.94
11.82
9.89
12.01
11.96
7.07
10.23
5.91
7.44
6.74
8.51
8.52
10.2
6.34
7.67
Fig 3 Relative changes in shear modulus of the upper trapezius
muscle resulting from dry needling and subject posture. (Left) Relative change from before to after dry needling. (Right) Relative change
from sitting to prone position.
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Quantification of stiffness in myofascial trigger points
devices because of the variability in stress dissipation by other
tissues (ie, skin, fat, fascia) and variable compression by the user,
which could artificially increase the tissue stiffness.12 In contrast,
supersonic shear imaging with shear-wave elastography requires
no manual compression because the deformation of tissue leading
to shear waves is created by an acoustic impulse that is generated
electronically and delivered through the ultrasound transducer.24
The recent observation of faster shear-wave propagation velocity
within the region of active MTrPs compared with the surrounding
region in the upper trapezius muscle, albeit using an external
vibrator, is in line with the idea that MTrPs are associated with
higher shear modulus.8 With the use of the current ultrasound
shear-wave elastography, tissue stiffness can be visualized in real
time, while the effects of dry needling are readily observed and
displayed via a color-coded map. The significant reduction in
shear modulus in the current study supports that shear modulus
measurements with this technology may be sensitive enough to
identify the reductions in tissue stiffness after dry needling.
Our findings show that tissue stiffness can be visualized in real
time, while the effects of dry needling are readily observed and
displayed via a color-coded map. The significant reduction
objectively quantified an immediate reduction in shear modulus
when going from a sitting to a prone position in all subjects who
had MTrPs in the upper trapezius before and after dry needling.
The relationship between sitting posture and neck pain has been
discussed in the literature,25,26 but the etiology is poorly defined.27
Few studies have examined the role muscles play in supporting the
body under gravitational forces. However, one study13 noted an
immediate decrease in the tone and stiffness of the upper trapezius, which occurred with a change from a sitting to a supine
position in healthy subjects, by using a handheld device to assess
indentation. These findings may lead to a better understanding of
how static postures can contribute to neck pain and the development of MTrPs, especially in those who work with visual
display terminals.
The muscle assessed in this study was a superficial muscle that
is easy to palpate. The same cannot be said for deeper muscles
such as those in the lumbar region or deep abdominal area.
Consequently, an inability to palpate and reproduce the classic
referral patterns is difficult to accomplish for the clinician. Shearwave elastography would provide such a means for an objective
evaluation of tissues of different types and depths, and a means to
determine the efficacy and longevity of therapeutic interventions.
Study limitations
The findings of this preliminary study cannot be generalized
because of the small sample size.
Conclusions
The preliminary results with a limited study population showed
that the shear modulus of the upper trapezius muscle with MTrPs,
measured with ultrasound shear-wave elastography, was significantly reduced after dry needling and in the prone position
compared with the sitting position, in agreement with reductions
in palpable stiffness. These preliminary findings suggest that dry
needling and the subject’s posture may affect the shear modulus of
MTrPs, and that shear modulus measurement with ultrasound
shear-wave elastography may be sensitive enough to detect
these effects.
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2149
Suppliers
a. SuperSonic Imagine, 11714 North Creek Pkwy N, Ste 150,
Bothell, WA 98011.
b. HBW Supply Inc, 1090 Investor Pl, San Jacinto Hemet,
CA 92583.
Keywords
Elasticity imaging techniques; Trigger points; Rehabilitation;
Ultrasonography
Corresponding author
Ruth M. Maher, PT, PhD, DPT, WCS, BCB-PMD, CEAS, Shenandoah University, Division of Physical Therapy, 333 W Cork St,
Suite 40, Winchester, VA 22601. E-mail address: [email protected].
Acknowledgments
We thank Supersonic Imagine, USA, for lending the ultrasound
device for the duration of this study.
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