Arch Phys Med Rehabil. 2016 (Feb); 97 (2): 316–337 ~ FULL TEXT
Alessandro Chiarotto, MSc, Ron Clijsen, PhD, Cesar Fernandez-de-las-Penas, PhD,
Marco Barbero, PT OMT
Department of Health Sciences,
Faculty of Earth and Life Sciences,
EMGO(+) Institute for Health and Care Research,
Amsterdam, The Netherlands.
OBJECTIVE: To retrieve, appraise, and synthesize the results of studies on the prevalence of active and latent myofascial trigger points (MTrPs) in subjects with spinal pain disorders.
DATA SOURCES: The databases PubMed, Embase, and CINAHL were searched, with no date or language restrictions. Search terms included controlled and free-text terms for spinal disorders and MTrPs. Further searches were conducted in Google Scholar and by contacting 3 experts in the field. Citation tracking of eligible studies was performed.
STUDY SELECTION: Two reviewers independently selected observational studies assessing the prevalence of active and/or latent MTrPs in at least 1 group of adults with a spinal disorder. Twelve studies met the eligibility criteria.
DATA EXTRACTION: Methodologic quality was assessed by 2 reviewers independently using a modified version of the Downs and Black checklist. Two reviewers also used a customized form to extract studies and subjects' characteristics and the proportions of subjects with active and/or latent MTrPs in each muscle assessed.
DATA SYNTHESIS: A meta-analysis was performed when there was sufficient clinical homogeneity in at least 2 studies for the same spinal disorder. The Grading of Recommendations Assessment, Development and Evaluation approach was used to rate the body of evidence in each meta-analysis. A qualitative description of the results of single studies was provided. Low-quality evidence underpinned pooled estimates of MTrPs in the upper-body muscles of subjects with chronic neck pain. The point prevalence of MTrPs in different muscles of other disorders (eg, whiplash-associated disorders, nonspecific low back pain) was extracted from single studies with low methodologic quality and small samples. Active MTrPs were found to be present in all assessed muscles of subjects diagnosed with different spinal pain disorders. Latent MTrPs were not consistently more prevalent in subjects with a spinal disorder than in healthy controls.
CONCLUSIONS: The MTrPs point prevalence estimates in this review should be viewed with caution because future studies with large samples and high methodologic quality are likely to change them substantially.
KEYWORDS: Low back pain; Neck pain; Prevalence; Rehabilitation; Trigger points; Whiplash injuries
From the Full-Text Article:
Spinal disorders are among the leading causes of years lived with
disability, with low back pain (LBP) ranking first and neck pain
(NP) ranking fourth worldwide.  The same disorders are also
majorly responsible for disability-adjusted life years.  The mean
lifetime activity-limiting prevalence of LBP is estimated to be
approximately 39% and that of NP is 23%, and the point prevalence
is approximately 18% and 14%, respectively. [3, 4] Cost-of-illness
studies have highlighted that costs associated with these disorders
represent a significant burden to society. [5, 6] Considering all these
factors together, it is apparent that research to increase our understanding
of the etiology of these disorders is critical.
A clinical sign in subjects with spinal disorders is the presence
of myofascial trigger points (MTrPs). [7–9] Expert-based definitions
of MTrPs identify these as hypersensitive spots within a taut
band of skeletal muscle that are painful on compression and which
can evoke referred pain.  From a clinical perspective, MTrPs can
be differentiated by manual assessment into active and latent. 
Active MTrPs elicit local and referred pain that reproduce the
symptoms that the patient suffered from and are recognized as a
familiar complaint, whereas latent MTrPs reproduce local and
referred pain that does not reproduce any spontaneous symptoms
perceived by the patient. 
The clinical distinction between active and latent MTrPs is
supported by histochemical findings showing that active MTrPs
contain higher levels of algogenic substances and chemical mediators
(eg, bradykinin, substance P, serotonin) than latent MTrPs and
body areas without MTrPs. [11, 12] Both active and latent MTrPs can
be involved in pain sensitization processes involving the central
nervous system, [13, 14] and these processes have been shown to be
altered in subjects diagnosed with different spinal disorders. [15–18]
Further, latent MTrPs can be contributors to musculoskeletal
signs and symptoms (eg, muscle imbalance, muscle weakness,
fatigability), as reported by recent studies. [19–21]
The presence of active MTrPs in a subject can lead to the
diagnosis of myofascial pain syndrome, which is considered to be
a major cause of musculoskeletal pain, and its prevalence in adult
subjects is reported to be high.  Several studies have reported the
prevalence of manually assessed active and latent MTrPs in
different muscles of subjects diagnosed with spinal disorders. To
our knowledge, however, no systematic reviews to date have
attempted to retrieve all of these studies to assess their methodologic
quality and summarize their findings.
The objective of our study was therefore to conduct a systematic
review of the literature with a meta-analysis to synthesize
the evidence on the prevalence of active and latent MTrPs in
subjects with spinal disorders. The body of evidence on the
prevalence of MTrPs was considered and analyzed separately for
each spinal pain disorder following diagnoses and definitions used
by the authors of the original studies (eg, LBP, NP, whiplashassociated
Three specific aims were defined for each disorder:
(1) to estimate the prevalence of active MTrPs in all evaluated muscles;
(2) to compare the prevalence of latent MTrPs in subjects diagnosed with different spinal disorders (eg, NP vs
(3) to compare the prevalence of latent MTrPs in both subjects diagnosed with a spinal disorder and healthy controls.
did not aim to compare the prevalence of active MTrPs between
subjects diagnosed with different spinal disorders or between
subjects with a spinal disorder and healthy controls because, by
definition, active MTrPs cannot be present in healthy subjects. [7–10]
Figure 1 is a flowchart of study retrieval, screening, and eligibility.
The 3 experts in the field we contacted did not identify any
additional studies besides those retrieved from the database
searches and citation tracking. Twelve studies met the eligibility
criteria and were included in this review [40–51]; 4 of these
studies [40, 42, 44, 49] were included in the meta-analyses. All studies
were cross-sectional and assessed the point prevalence of MTrPs.
The characteristics of these studies (ie, spinal disorders involved,
diagnostic criteria, muscles assessed, country, setting) are summarized
in table 1. One study compared the point prevalence of
MTrPs in subjects with NP and WAD,  8 compared the prevalence
of MTrPs in ≥1 group of subjects with a spinal disorder and
healthy controls, [42–47, 49, 51] and the remaining 3 assessed the
prevalence of MTrPs only in a group of subjects with a spinal
disorder. [41, 48, 50]
Five studies were conducted in subjects with
NP [40, 42–44, 49]; 3 included subjects with WAD [40, 43, 45]; 1 included a
mixed population of subjects with spinal pain ; 2 included subjects
with NSLBP [46, 47]; 1 included subjects with cervicogenic
headache ; 1 included subjects with lumbar disk herniation ;
and 1 included subjects with cervical radiculopathy (CR). 
Sample size, sex age, and other characteristics of the subjects
included in the studies are shown in table 2.
Diagnostic criteria for MTrPs varied widely across the
studies. Six studies [40, 42, 44, 45, 49, 51] adopted expert-based definitions for active and latent MTrPs ; Iglesias-Gonzalez et al 
adopted the same criteria but with the exclusion of local twitch response as a diagnostic criterion; Samuel et al  used different criteria for active MTrPs; and the other 4 studies [41, 43, 46, 48] did not make a clear distinction between active and latent MTrPs (see table 1).
Methodologic quality assessment
Table 3 presents the methodologic quality assessment of the 12
included studies. Because 1 reviewer (A.C.) was an author of an
eligible study, he was not involved in the quality assessment of
that study, which was assessed by the third reviewer (R.C.).
Overall, the studies presented low methodologic quality, with only
2 meeting >50% of the applicable criteria of the checklist. [40, 42]
Seven criteria were not applicable to 3 studies because they
included only 1 group of subjects. [41, 48, 50] All but 1 study  had a
clear description of the hypothesis/aim/objective (ie, item 1), and
all but 2 studies [41, 43] clearly presented the inclusion and exclusion
criteria of the subjects included (ie, item 3). Item 8 regarding the
description of the sampling method for the recruitment of subjects
from the source population was not met by any study, likewise for
item 13 on the accuracy of the main outcome measures (ie, MTrPs
diagnosis) and item 16 on the sample size calculation. Only Hua
et al  reported on the proportion of recruited subjects who agreed
to participate (ie, item 9). Items 14 and 15 on selection bias
regarding the recruitment of subjects and controls from the same
population and over the same time period were met by a small
minority of the studies (see table 3). The distribution of principal
confounders in each study group (ie, item 4) was met by De-la-
Llave-Rincon et al,  but the other studies did not report on
some key potential confounders (ie, body mass index, anxiety,
depression, pain hypersensitivity).
Among the 5 studies that reported on the point prevalence of
MTrPs in subjects with NP, 4 studies included subjects with
chronic NP; of these, 2 studies [40, 42] had high methodologic quality
and the other 2 studies [44, 49] had low quality (see table 3). Ettlin
et al  did not report the inclusion criteria or clinical characteristics
of the included subjects with NP, had low methodologic
quality, did not make a distinction between active and latent
MTrPs, and did not make a distinction between the diagnosis of
myofascial pain syndrome and MTrPs. For these reasons, this
study was excluded from the meta-analyses, and its results are not
presented here because they were poorly informative.
There was low-quality evidence that the point prevalence of
active MTrPs in 91 subjects with chronic NP is 38.5% (95% CI,
29.1–48.9) on the right upper trapezius, 29.8% (95% CI, 21.3–
40.0) on the left trapezius, 16.9% (95% CI, 10.4–26.2) on the
right levator scapulae, 14.8% (95% CI, 7.7–26.7) on the left levator
scapulae, 22.0% (95% CI, 14.5–32.1) on the right
sternocleidomastoid, and 19.8% (95% CI, 12.6–29.6) on the left
sternocleidomastoid (fig 2). Downgrading of the quality of evidence
was caused by low methodologic quality and imprecision.
Low-quality evidence (because of inconsistency and lack of precision)
was also found on the point prevalence of active MTrPs on
the temporalis muscle of 76 subjects with chronic NP, resulting in
pooled estimates of 11.9% (95% CI, 1.0–63.6) on the right side
and 11.2% (95% CI, 1.2–56.9) on the left side (fig 3). The point
prevalence for active MTrPs on other muscles is summarized in
table 4, where it can also be seen that all results were extracted
from studies with small samples.
ORs with 95% CIs were calculated for a high-quality study 
that compared the presence of latent MTrPs in subjects with
chronic NP and chronic WAD (table 5). A significant difference
was found for the left sternocleidomastoid, indicating that
subjects with chronic NP had lower odds than those with WAD
to display a latent MTrP on this muscle. For all other muscles,
no significant differences were found regarding the presence of
latent MTrPs between subjects with NP and those with WAD
(see table 5).
There was low-quality evidence showing that pooled ORs for
the presence of latent MTrPs on both sides of the upper trapezius
and levator scapulae were not statistically different between
subjects with chronic NP and healthy controls (fig 4). Reasons
for downgrading evidence quality were low methodologic
quality and small sample sizes. The same level of evidence was
found for pooled ORs showing that subjects with chronic NP
have significantly higher odds than healthy controls to have
latent MTrPs on both sides of the sternocleidomastoid (see
One study40 of high methodologic quality found that subjects
with chronic NP had significantly higher odds than healthy controls
to have latent MTrPs on the masseter and temporalis muscles
(see table 5). Munoz-Munoz et al  (low quality) did not find a
significant difference for latent MTrPs on other muscles between
subjects with chronic NP and healthy subjects (see table 5). All of
these results were extracted from studies with small samples
(see table 2).
One study  of high quality and 1 study  of low quality reported
on the point prevalence of MTrPs in subjects with chronic WAD;
another study  with low quality assessed subjects with acute
WAD. The results of Ettlin et al  are not presented here because
they made no distinction between active and latent MTrPs and the
diagnosis of myofascial pain syndrome and MTrPs. Statistical
pooling of the other 2 studies [40, 45] was not feasible because of
ample heterogeneity in the symptom duration of subjects with
WAD (see table 2).
ORs with 95% CIs were calculated for the comparisons of
active MTrPs in subjects with chronic WAD and chronic NP and
the comparisons of latent MTrPs in subjects with acute WAD and
healthy controls (table 6). The point prevalence of active MTrPs in
subjects with WAD is also shown in table 6. Table 5 presents the
ORs with 95% CIs for the study  that compared the presence of
latent MTrPs between subjects with chronic NP and chronic
WAD. Fernandez-Perez et al,  in a study of low quality and small
sample size, showed significantly greater odds of displaying latent
MTrPs on the right upper trapezius, right sternocleidomastoid, and
right scalene in subjects with WAD than in healthy controls
(see table 6).
One study  with low methodologic quality reported on the
prevalence of MTrPs in 11 subjects with cervicogenic headache.
This study did not make a distinction between active and latent
MTrPs, and it was not possible to extract this difference from the
article because it was not clear whether symptom recognition was
used for the diagnosis of MTrPs. For this reason, the results of this
study are not presented here.
Sari et al  reported on the prevalence ofMTrPs in 244 subjects with
CR compared with 122 healthy controls. This study was low quality
and did not make a distinction between right/left or symptomatic/
asymptomatic muscle sides. Point prevalences for activeMTrPs were
as follows: 51.2%on the total sample, 16.3% on the levator scapulae,
14.7% on the splenius capitis, 14.3% on the rhomboid minor, 13.5%
on the upper trapezius, 10.2% on the rhomboid major, and 8.6% on
the multifidus. No significant differences between subjects with CR
and controls were found for latent MTrPs on the levator scapulae
(OR = .80; 95% CI, .52–1.26), splenius capitis (OR = 1.02; 95% CI,
.58–1.83), rhomboid minor (OR = 1.15; 95% CI, .69–1.92), upper
trapezius (OR = .83; 95% CI, 0.55–1.25), and rhomboid major
(OR = 1.37; 95% CI, 0.59–3.18). Subjects with CR displayed
significantly lower odds than controls with latent MTrPs on the
multifidus (OR = .48; 95% CI, .25–.91).
Nonspecific low back pain
Two studies [46, 47] with low methodologic quality reported on the
prevalence of MTrPs in subjects with NSLBP: one included only
subjects with chronic NSLBP,  and the other included only
acute and subacute NSLBP.  The results of the latter are not
presented because a distinction between active and latent MTrPs
could not be established from the diagnostic criteria used (see
table 1). The point prevalences of active MTrPs from the study of
Iglesias-Gonzalez  in 42 subjects with chronic NSLBP are
shown in table 7. No ORs were calculated for latent MTrPs in
subjects with NSLBP and healthy controls because of the differences
in assessing more/less painful or dominant/nondominant
muscle sides. Overall, latent MTrPs tended to be more
prevalent in subjects with chronic NSLBP than in healthy
subjects (see table 7).
Lumbar disk herniation
Samuel  (low methodologic quality) assessed the point prevalence
of active MTrPs in 60 subjects diagnosed with lumbar disk
herniation. In this study, no distinction between right/left or
symptomatic/asymptomatic muscle sides was made, and some
criteria used in other studies for the diagnosis of active MTrPs
were not used (see table 1). Point prevalences were as follows:
50.0% tibialis anterior, 67.7% extensor hallucis longus, 3.3%
extensor digitorum longus, 81.7% gluteus maximus, 13.3%
gluteus minimus, 48.3% hamstring, 80.0% gastrocnemius, and
Mixed population of spinal disorders
One study  of low quality assessed the presence of MTrPs in a
mixed sample of subjects with chronic spinal pain. In this study no
distinction between active and latent MTrPs was made, and its
results are not presented here.
In this systematic review we aimed to synthesize the evidence
on the prevalence of active and latent MTrPs in spinal disorders
by including 12 cross-sectional studies assessing point prevalence
in 6 different spinal pain disorders. Low-quality evidence
was found for the pooled point prevalence of active MTrPs of
different muscles in subjects with chronic NP. Point prevalences
of active MTrPs in subjects with WAD and NSLBP were
extracted from single studies that had low quality and/or very
small samples. In 1 study of high methodologic quality,  no
significant differences were found in the prevalence of latent
MTrPs between subjects with chronic NP and those with
chronic WAD. There was low-quality evidence that subjects
with chronic NP had higher odds than healthy controls to
display latent MTrPs on the sternocleidomastoid, but not on
upper trapezius and levator scapulae. Small sample sizes and/or
low methodologic quality were a constant characteristic of the
findings on latent MTrPs taken from individual studies on
different spinal disorders (ie, NP, WAD, NSLBP, CR). Future
studies of high methodologic quality and with larger samples
are very likely to substantially change the point prevalence
estimates of MTrPs presented here.
Of the 12 studies included in this review, 10 studies [41, 43–51]
had low methodologic quality (see table 3). Several items
were not met by any study, and this emphasizes that future
studies on the prevalence of MTrPs in spinal disorders should
attempt to meet these criteria. For example, a lack of information
on the sampling method used to recruit subjects from the
source population, and on the proportion of those recruited
agreeing to participate, might strongly limit the generalizability
of findings. Information regarding the recruitment of subjects
and controls from the same source population should also be
reported because a failure to do so might hinder the assessment
of selection bias in these studies. The measurement properties
of active and latent MTrPs diagnostic criteria were not presented
in any of the studies. This lack is even more important if
we consider that 2 systematic reviews [52, 53] reported limited
reliability for MTrPs criteria. However, in line with more recent
individual studies, [54, 55] these reviews also highlighted that
reliability was strongly dependent on the selected muscles and
on other variables (eg, examiners’ training and experience).
Detailed reference to this information should be provided in
future studies because this would confirm that researchers are at
least aware of this potential limitation of MTrPs assessment.
Future studies comparing the prevalence of latent MTrPs in 2
distinct groups should calculate their sample size beforehand to
reduce the chances of finding false significant results as a result of
poor statistical power (ie, type I error). Another crucial aspect that
should be better addressed by future studies is the reporting of
potential key confounders when comparing the prevalence of
MTrPs in 2 distinct groups of subjects. In fact, patients’
morphologic features or impairments of the nociceptive system
may limit the applicability of the diagnostic criteria for MTrPs.
Detection of the taut band can be difficult in subjects with a high
body mass index because of the presence of subcutaneous fat.
Moreover, criteria based on pain provocation (ie, spot tenderness,
pain recognition, referred pain) may be affected by general hypersensitivity
or the presence of comorbid conditions that may
alter the perception or reporting of pain (ie, depression,
In 4 studies, [41, 43, 46, 48] a clear distinction between active and
latent MTrPs was not made, making it difficult to extract
meaningful data from these studies. The distinction between
active and latent MTrPs, initially made for clinical purposes by
experts in the field,  has been supported by studies showing that
the 2 phases/stages of MTrPs present different histochemical
findings. [11, 12] Two other studies [50, 51] did not present the assessment
of MTrPs on each side of each muscle (or did not distinguish
between painful sides), making the interpretation of the
results more difficult. This variability in the diagnostic criteria
for MTrPs is not new  and can strongly hinder the synthesis of
data from different studies. Such variability is probably the
result of lack of data on the criterion validity of MTrPs diagnostic
criteria because of the absence of a feasible and accepted
reference standard to estimate indices (eg, sensitivity, specificity).
In this regard, a future study might focus on reaching an
international and multidisciplinary consensus on the diagnostic
criteria for MTrPs (eg, Delphi survey), with the goal of standardizing
their assessment in clinical practice and research.
Overall, good quality studies of the reliability of different sets of
criteria are needed to further strengthen or weaken the findings
of the available literature. [52–55, 57]
Pooled estimates of the point prevalence of active MTrPs in
subjects with chronic NP on the upper trapezius, levator scapulae,
sternocleidomastoid, and temporalis showed that the
highest prevalence was on the upper trapezius (see figs 2 and 3).
Despite low-quality evidence, these estimates may be to some
extent accurate if we consider the high prevalence of NP and
shoulder pain in both the working and general population. [58, 59]
These painful syndromes are common among office workers,
and upper trapezius myalgia is the most frequent neck complaint
in occupational groups. [60–62] Results from single studies showed
the highest point prevalence for active MTrPs on the suboccipital
muscles (see table 4), but all estimates were extracted from
studies with very small samples. The significant difference in the
prevalence of latent MTrPs on the left sternocleidomastoid between
subjects with chronic WAD and chronic NP can be
considered a spurious finding, considering that no differences
were found for all other muscles and that this study included a
small sample.  Future studies with larger samples are needed to
confirm or refute this peculiar finding for the left sternocleidomastoid.
The same applies for meta-analyses or results of individual
studies comparing the prevalence of latent MTrPs in
subjects with NP and healthy controls (see fig 4 and table 5)
because these were extracted from very small samples. Future
observational studies should adopt large sample sizes and have a
higher methodologic quality to provide more precise estimates of
the point prevalence of both active and latent MTrPs in subjects
Castaldo et al  showed that active MTrPs appear to have a
higher point prevalence in subjects with chronic WAD than in
those with chronic NP (see table 6). If the presence of MTrPs is
considered a possible indicator of central sensitization, [13, 14]
these results could be explained by the enhanced degree of
central sensitization of subjects with WAD compared with those
with NP. [18, 28, 63] However, more studies are needed to confirm or
reject the findings obtained from the relatively small sample of
this study. The same consideration applies to the study of
Fernandez-Perez,  in which latent MTrPs were compared
between subjects with acute WAD and healthy controls;
although some differences between groups were found
(see table 6), more studies with larger samples are
Several health care providers recognize the clinical relevance
of the MTrP concept; however, the validity of this concept is
discussed in the scientific community, and controversies still
exist. [64–66] To add to this, the aforementioned methodologic limitations
of existing studies on spinal disorders strongly influence
their findings. For this reason, the apparent and constant presence
of the MTrP phenomenon in different spinal disorders emerging
from this review (see figs 2–4 and tables 4–7) should be
considered with caution at this stage.
All of the elements described here highlight the need to
establish the relevance of MTrPs for clinical practice. Nevertheless,
we do not know whether MTrPs should be considered an
epiphenomenon of the painful conditions or a relevant comorbidity.
Clinical guidelines for spinal disorders do not usually
consider either MTrP evaluation or MTrP treatment. To improve
rehabilitation for spinal disorders, it may be important to
establish whether MTrP treatment should be taken into account
or not; more specifically, it appears crucial to strengthen the
construct validity of the MTrP diagnosis and to reach a consensus
on a set of MTrP diagnostic procedures.
We acknowledge as a limitation of this systematic review that
the reviewer (A.C.), who was an author of an eligible study,
although he was excluded from the quality assessment of that
particular study, could have influenced the assessment of the
other studies. However, given the circumstances, it was not
practical for this review to find a different reviewer from the
author originally designed for quality assessment of all of the
studies. It should also be considered that the approach of
excluding a reviewer only from rating his own study is not new
in the literature, and it has been adopted also in Cochrane
Reviews on the effectiveness of health interventions. [67, 68]
This systematic review shows that active and latent MTrPs can
be present in different spinal disorders (eg, NP, WAD, NSLBP).
However, these findings are at best underpinned by pooled
estimates of point prevalence that are based on low-quality
evidence, according to the Grading of Recommendations
Assessment, Development and Evaluation approach. Most of the
estimates for both active and latent MTrPs are based on individual
studies with very small sample sizes and low methodologic
quality. Future studies with large samples and high
methodologic quality are needed to provide more reliable and
precise estimates on the point prevalence of MTrPs in spinal
disorders. Moreover, to facilitate comparison of findings and
data pooling, there is an urgent need to standardize the assessment
of MTrPs across clinical studies.
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