Lancet. 2009 (Dec 5); 374 (9705): 1897–1908 ~ FULL TEXT
Dr Roberta T Chow, MBBS , Prof Mark I Johnson, PhD, Prof Rodrigo AB Lopes-Martins, PhD, Prof Jan M Bjordal, PT
Nerve Research Foundation,
Brain and Mind Research Institute,
University of Sydney,
Sydney, NSW, Australia.
BACKGROUND: Neck pain is a common and costly condition for which pharmacological management has limited evidence of efficacy and side-effects. Low-level laser therapy (LLLT) is a relatively uncommon, non-invasive treatment for neck pain, in which non-thermal laser irradiation is applied to sites of pain. We did a systematic review and meta-analysis of randomised controlled trials to assess the efficacy of LLLT in neck pain.
METHODS: We searched computerised databases comparing efficacy of LLLT using any wavelength with placebo or with active control in acute or chronic neck pain. Effect size for the primary outcome, pain intensity, was defined as a pooled estimate of mean difference in change in mm on 100 mm visual analogue scale.
FINDINGS: We identified 16 randomised controlled trials including a total of 820 patients. In acute neck pain, results of two trials showed a relative risk (RR) of 1.69 (95% CI 1.22-2.33) for pain improvement of LLLT versus placebo. Five trials of chronic neck pain reporting categorical data showed an RR for pain improvement of 4.05 (2.74-5.98) of LLLT. Patients in 11 trials reporting changes in visual analogue scale had pain intensity reduced by 19.86 mm (10.04-29.68). Seven trials provided follow-up data for 1-22 weeks after completion of treatment, with short-term pain relief persisting in the medium term with a reduction of 22.07 mm (17.42-26.72). Side-effects from LLLT were mild and not different from those of placebo.
INTERPRETATION: We show that LLLT reduces pain immediately after treatment in acute neck pain and up to 22 weeks after completion of treatment in patients with chronic neck pain.
From the FULL TEXT Article:
Chronic pain is predicted to reach epidemic proportions in
developed countries with ageing populations in the next
30 years.  Chronic neck pain is a highly prevalent condition,
aff ecting 10–24% of the population. [2–5] Economic costs of
this condition are estimated at hundreds of millions of
dollars,2 creating an imperative for evidence-based, costeff
ective treatments. Low-level laser therapy (LLLT) uses
laser to aid tissue repair,  relieve pain,  and stimulate
acupuncture points.  Laser is light that is generated by
high-intensity electrical stimulation of a medium, which
can be a gas, liquid, crystal, dye, or semiconductor.  The
light produced consists of coherent beams of single
wavelengths in the visible to infrared spectrum, which can
be emitted in a continuous wave or pulsed mode. Surgical
applications of laser ablate tissue by intense heat and are
different from LLLT, which uses light energy to modulate
cell and tissue physiology to achieve therapeutic benefi t
without a macroscopic thermal effect (sometimes termed
cold laser). LLLT is non-invasive, painless, and can be easily
administered in primary-care settings. Incidence of adverse
effects is low and similar to that of placebo, with no reports
of serious events. [10, 11]
Research into the use of LLLT for pain reduction [12, 13] and
tissue repair [14, 15] spans more than 30 years. However,
reports do not identify this therapy as a potential
treatment option,  possibly because of scepticism about
its mechanism of action and effectiveness.  Research
from the past decade suggests that LLLT produces antiinfl
ammatory effects, [18–21] contributing to pain relief.
Cochrane reviews of the efficacy of LLLT in low-back
pain  and rheumatoid arthritis  have been unable to
make firm conclusions because of insufficient data or
conflicting findings. However, effectiveness depends on
factors such as wavelength, site, duration, and dose of
LLLT treatment. Adequate dose and appropriate
procedural technique are rarely considered in systematic
reviews of electrophysical agents. Research into the doseresponse
profile of LLLT suggests that different
wavelengths have specific penetration abilities through
human skin. [17, 24, 25] Thus, clinical effects could vary with
depth of target tissue. We have shown the importance of
accounting for dose and technique in systematic reviews
of transcutaneous electrical nerve stimulation  and
LLLT, [11, 21] and our approach is an acknowledged means of
establishing efficacy. 
The only systematic review focusing solely on LLLT in
treatment of neck pain included four randomised
controlled trials, and concluded that there was evidence
of short-term benefit of LLLT at infrared wavelengths of
780, 810–830, and 904 nm.  A Cochrane review of
physical medicine for mechanical neck disorders, since
withdrawn because much time had passed without an
update, included three LLLT trials, for which outcomes
did not diff er from those of placebo.  The same
investigators did a meta-analysis  of 88 randomised
controlled trials of conservative treatments for acute,
subacute, and chronic mechanical neck disorders, which
included eight trials using LLLT. They concluded that
LLLT has intermediate and long-term benefits.
These reviews did not identify treatment variables
associated with positive outcomes, include non-English
language publications, or quantitatively assess data. [28, 30]
We have therefore undertaken a new systematic review
and meta-analysis of LLLT in neck pain to establish
whether LLLT relieves acute and chronic neck pain and
to systematically assess parameters of laser therapy to
identify treatment protocols and dose ranges (therapeutic
windows) associated with positive outcomes.
Search strategy and selection criteria
We did a search of published work without language
restriction using Medline (January, 1966, to July, 2008),
Embase (January, 1980, to July, 2008), Cinahl (January,
1982, to July, 2008), the Physiotherapy Evidence Database
(January, 1929, to July, 2008), Biosis (January, 1926, to July,
2008), Allied and Complementary Medicine (January,
1985, to July, 2008), and the Cochrane Central Register of
Controlled Trials (second quarter of 2008). Keywords used
for neck pain and related conditions were: “neck pain/
strain”, “cervical pain/strain/syndrome”, “cervical spondylosis/
itis”, “cervicobrachial (pain/disorder/syndrome)”,
“myofascial (pain/disorder/syndrome)”, “trigger points”,
“fi bromyalgia”, “whiplash/WAD”, “osteoarthritis/arthritis”,
and “zygaphophyseal/ZG joints”. We combined these
keywords with synonyms for LLLT: “low-level/low-energy/
infrared/diode/semiconductor/soft or cold or mid/
visible”; “laser therapy”, “(ir)radiation”, “treatment”; “lowenergy
photon therapy”; “low output laser”; “LLLT”;
“LILT”; “LEPT”; “LELT”; “LILI”; “LELI”; “LPLI”; “biostimulation”;
“light therapy”; “phototherapy”; “narrow band light
therapy”; “904 nm”; “830 nm”; “632 nm”; “1064 nm”;
“GaAs”; “GaAlAs”; “HeNe”; and “defocused CO2”. We
consulted experts and searched reference lists of retrieved
reports and textbooks for additional references.
Citations were screened and full reports of potentially
relevant studies obtained. We applied inclusion and
exclusion criteria, assessed methodological criteria, and
extracted data including trial characteristics, demographic
data, laser parameters, pain outcome measures, and cointerventions.
Non-English language studies were
translated by JMB.
We included randomised or quasi-randomised
controlled trials of LLLT for acute or chronic neck pain as
defi ned by trial investigators, and identified by various
clinical descriptors included under the term non-specific
neck pain.  These diagnostic labels included neck strain,
neck sprain, mechanical neck disorders, whiplash, neck
disorders, and neck and shoulder pain. We also used
surrogate terms for neck pain, such as myofascial pain
and trigger points. [32, 33] Study participants were restricted
to those aged 16 years and older. We excluded studies in
which specific pathological changes could be identified,
such as systemic inflammatory conditions — eg,
rheumatoid arthritis, localised or generalised
fibromyalgia, neck pain with radiculopathy, and neck
pain related to neurological disease. We excluded
abstracts and studies for which outcome measures for
neck pain could not be separated from data for other
regions of the body. Two reviewers (RTC, JMB)
independently undertook the search of published work,
screened studies, and extracted data. Any disagreements
between reviewers were resolved by consensus with other
team members acting as arbiters (RABL-M, MIJ).
Investigators had to have used a laser device that
delivered irradiation to points in the neck identified by
tenderness, local acupuncture points, or on a grid at
predetermined points overlying the neck. Control groups
had to have been given either placebo laser in which an
identical laser device had an active operating panel with
the laser emission deactivated or an active treatment
control (eg, exercise). We also included trials in which an
active control was used as a co-intervention in placebo
and real laser groups.
To be eligible for inclusion, a study had to compare
pain relief along a 0–100 mm visual analogue scale, a
numerical rating scale, or by patient-reported
improvement (eg, categorical report of no change to
complete relief of pain) as a primary outcome measure
before and after laser therapy. Functional measures of
disability (eg, neck pain disability questionnaire) were
assessed as secondary outcome measures. We also
examined adverse events where reported, although did
not specify these a priori. Duration of follow-up was
assessed and defi ned as short term (<1 month), mediumterm
(1–6 months), and long term (>6 months).
Assessment of methodological quality and heterogeneity
Reviewers assessed all studies for methodological quality
on the basis of Jadad criteria (maximum score 5).  Jadad
criteria allocate a point each for randomisation, doubleblind
design, and description of dropouts. If
randomisation and double-blind concealment are
assured, an additional 2 points are added. If randomisation
or double-blind concealment is not assured, a point is
deducted for each. A trial with a score of 3 or more is
regarded as high quality. Data from trials with scores of 3
or more were grouped and analysed separately from
those scoring less than 3.
We assessed clinical heterogeneity by considering
population difference in age, sex, duration of symptoms,
and outcomes. Clinical judgment was used to establish
whether trials were sufficiently similar to allow pooling
of data. The specific parameters of laser devices,
application techniques, and treatment protocols were
extracted and tabulated by laser wavelength. Details for
power output, duration of laser irradiation, number of
points irradiated, and frequency and number of
treatments were listed. When specific details were not
reported, calculations were made from those described
in the report when possible. When crucial parameters
were not reported, we contacted manufacturers of laser
devices and trial investigators to obtain missing
information. Not all data were available because of the
time elapsed since publication of some studies.
Heterogeneity was qualitatively assessed for these factors
by an expert in laser therapy (JMB).
We used five levels of evidence to describe whether
treatment was beneficial: strong evidence (consistent
findings in several high-quality randomised controlled
trials); moderate evidence (findings from one highquality
randomised controlled trial or consistent findings
in several low-quality trials); limited evidence (one lowquality
randomised trial); unclear evidence (inconsistent
or contradictory results in several randomised trials); and
no evidence (no studies identified). 
effect size for the primary outcome, pain intensity, was
defi ned as a pooled estimate of the mean difference in
change in mm on a 100 mm visual analogue scale
between the mean of the treatment and the placebo
groups, weighted by the inverse of the SD for every
study — ie, weighted mean difference of change between
groups. Variance was calculated from the trial data and
given, with 95% CI, in mm on visual analogue scale. For
categorical data, reported pain relief was dichotomised
into two categories (improvement or no improvement),
and we calculated relative risk (RR) of improvement, with
95% CI. For the secondary outcome, disability, effect size
was defi ned as the standardised mean difference, which
was a combined outcome measure without units — ie, the
standardised mean difference in change between active
laser groups and placebo groups for all included trials,
weighted by the inverse of the variance for each study. 
Mean differences of change for laser-treated and control
groups and their respective SDs were included in the
statistical pooling. If variance data were not reported as
SDs, they were calculated from the trial data of sample size
and other variance data values such as p values, t values,
SE, or 95% CI. Results were presented as weighted mean
difference between laser-treated and control with 95% CI
in mm on visual analogue scale — ie, as a pooled estimate
of the mean difference in change between the laser-treated
and control groups, weighted by the inverse of the variance
for each study.  Statistical heterogeneity was assessed for
significance (p<0·05) with Revman 4.2, and χ2 and F values
greater than 50%. For categorical data, we calculated
combined RRs for improvement, with 95% CI. A fixed
effect model was used unless statistical heterogeneity was
Significant (p<0·05), after which a random effects model
was used. Publication bias was assessed by graphical plot. 
Revman 4.2 was used for statistical analysis and Microsoft
Excel 2003 (version 11) to plot dose-response curves.
Role of the funding source
There was no funding source for this study. The
corresponding author had full access to all the data in the
study and had final responsibility for the decision to
submit for publication.
We identified 16 randomised controlled trials of a possible
38 that were suitable for inclusion, and that included
820 patients (figure 1). Two trials [39, 40] provided data for laser
therapy of acute neck pain, one treating acute whiplashassociated
disorders and one treating acute neck pain of no
defi ned cause. The other 14 trials reported response of
chronic non-specific neck pain without radiculopathy to
laser therapy. [13, 41–53] Of the studies included, 648 (79%) of the
sample of patients with chronic neck pain were women,
and patients had a mean age of 43 years (SD 9·8), mean
symptom duration of 90 months (SD 36·9), and mean
baseline pain of 56·9 mm (SD 7·5) on a 100 mm visual
analogue scale in any trial. Co-interventions were
inconsistently reported (Table 1). Ten trials reported
co-interventions, and six studies did not report or limit
co-interventions. Of the studies reporting co-interventions,
five groups of investigators explicitly excluded use of
concurrent physical therapies, and four excluded use of
non-steroidal anti-inflammatory drugs. Four studies
allowed use of simple analgesic drugs as needed.
Methodological quality assessment values for the trials by
Jadad scoring ranged from 0 to 5 (table 1).
Analysis of categorical data for immediate before and
after LLLT effects showed that LLLT groups in the two
trials [39, 40] of acute neck pain had a Significant RR of 1·69
(95% CI 1·22–2·33) for improvement immediately after
treatment versus placebo (figure 2). Methodological
quality varied between these two studies. Five trials of
chronic neck pain reported categorical data, and all were
high-quality trials with methodological scores of 3 or
more. RR of pain improvement with LLLT was 4·05
(2·74–5·98) compared with placebo at the end of
treatment (figure 3).
Analysis of data from visual analogue scale showed that
in patients in 13 groups in 11 trials, irrespective of
methodological quality, pain intensity was reduced by a
mean value of 19·86 mm (10·04–29·68) compared with
placebo groups (figure 4). Seven trials with eight LLLT
groups provided follow-up data for 1–22 weeks after end
of treatment (figure 5). The pain-relieving effect in the
short term (<1 month) persisted into the medium term
(up to 6 months). Five studies provided evidence for
improvement in disability at end the of LLLT treatment
(figure 6). Several questionnaire-based outcome measures
were used—specifically, the neck pain and disability
scale,  Northwick Park neck pain questionnaire,  short
form [36, 56] Nottingham health profile,  and neck disability
Positive publication bias, which tends to exclude
negative studies, was not apparent on testing (figure 7). 
The plot has an aggregation in the lower left quadrant of
several small studies with results showing no or only
small changes in visual analogue scale.  If publication
bias towards only positive studies was present, few
studies would lie in this position and small studies would
have exaggerated positive outcomes. The slight
asymmetry might be partly due to a negative publication
bias, the small number of studies, and because we have
included the most reported studies so far.
We subgrouped trials according to a-priori protocol in
acute and chronic categories for the statistical analyses.
Within these categories, we noted small variations
between trials in patient characteristics such as baseline
pain, symptom duration, age, and sex, and we did not
detect any clinical heterogeneity (data not shown). Laser
parameters and application techniques, including
treatment protocols, were heterogeneous (Table 2). Laser
irradiation was applied to an average of 11 points (range
3–25) in the neck. Energy delivered per point ranged
from 0·06 to 54·00 J, with irradiation durations of
1–600 s. Patterns of treatment ranged from a one-off
treatment to a course of 15 treatments, which were
administered daily to twice a week. On average,
participants received a course of ten treatments. Visible
(632·8 and 670·0 nm) and infrared (820–830, 780, and
904 nm) wavelengths were used at average power outputs
ranging from 4 to 450 mW, in pulsed and continuous
When trials with Significant results in favour of LLLT
were subgrouped by wavelength, doses and irradiation
times seemed fairly homogeneous within narrow ranges
(Table 3). We noted a distinct dose-response pattern for
each wavelength for which LLLT is effective within a
narrow therapeutic window. For 820–830 nm, mean dose
per point ranged from 0·8 to 9·0 J, with irradiation times
of 15–180 s. For 904 nm doses, mean dose per point was
0·8–4·2 J, with irradiation times of 100–600 s.
Investigators who used doses outside the minimum
(0·075 J and 0·06 J) [40, 49] and maximum (54 J)44 limits of
these ranges did not show any effect of LLLT, lending
further support to a dose-dependent response for LLLT in
Significant heterogeneity exists in categorical data for
improvement from two studies39,40 of acute neck pain
(p=0·003, χ2=8·86, I2=88·7%). This finding could be
attributable to the low dose per point used in one study. [40, 62]
We noted no heterogeneity between trials of chronic neck
pain reporting on categorical data (p=0·37, χ2=4·31,
For continuous data from 100 mm visual analogue
scale in chronic neck pain, we detected Significant
heterogeneity across all wavelengths (p<0·0001,
χ2=137·76, I2=90·6%). However, when heterogeneity was
addressed separately by wavelengths, most heterogeneity
could be accounted for by variations in doses and
application procedures. Removal of the study  that used
a very high dose from the disability analysis eliminated
statistical heterogeneity (p=0·31, χ2=3·61, I2=16·9%).
For pain intensity on 100 mm visual analogue scale for
820–830 nm wavelength, this study caused heterogeneity
together with results of a second study  that showed a
highly Significant effect, without obvious reasons for
heterogeneity. After removal of both studies from the
820–830 nm analysis, statistical heterogeneity was
eliminated (p=0·12, χ2=10·20, I2=41·2%), but the overall
effect remained similar, with narrower confi dence
intervals after (22·0 mm [14·5–29·6]) than before
(21·6 mm [10·3–32·9]) removal.
For 904 nm wavelength, statistical heterogeneity was
evident for analysis of pain intensity on 100 mm visual
analogue scale (p=0·00001, χ2=28·37, I2=89·4%). The
only study in the review using a scanning application
procedure in contact with the skin had weaker than
average results.  Contrary to other laser application
procedures, this method irradiates the target area
intermittently. Few studies compare scanning
irradiation with stationary irradiation, and most LLLT
studies have used a stationary laser beam. Another
study using 904 nm wavelength  with non-Significant
results has been criticised for absence of laser testing
and calibration, and the actual dose used remains
uncertain.  Removal of these two trials from the 904 nm
analysis of pain reduction on 100 mm visual analogue
scale increased the overall effect from 20·6 mm
(95% CI 5·2–36·2) to 37·8 mm (25·4–50·1).
50% of trials did not report side-effect data. Side-effects
reported included tiredness, nausea, headache, and
increased pain, but were mild and, apart from one study
in which unusual tiredness occurred more in the laser
group than in the placebo group (p>0·01),42 did not differ
from those of placebo.
Our results show moderate statistical evidence for efficacy
of LLLT in treatment of acute and chronic neck pain in the
short and medium term. For chronic pain, we recorded an
average reduction in visual analogue scale of 19·86 mm
across all studies, which is a clinically important change. [64, 65]
Categorical data for global improvement also Significantly
favoured LLLT. From our analysis, 820–830 nm doses are
most effective in the range of 0·8–9·0 J per point, with
irradiation times of 15–180 s. At 904 nm, doses are slightly
smaller (0·8–4·2 J per point), with slightly longer
irradiation times (100–600 s) than at 820–830 nm.
Our findings build on those of previous reviews of
LLLT [28, 30] by including non-English language studies,
laser acupuncture studies in which local points were
treated, and a quantitative analysis. Our search strategy
has identified a greater number of studies than have
previous reviews, and draws attention to the intrinsic
diffi culties in searching the topic of LLLT. specifically,
no accepted terminology exists for laser therapy. We
have overcome this limitation by using as wide a range
of synonyms as possible.
Moreover, many apparently disparate diagnostic
terms are applied to patients presenting with neck pain.
These terms suggest distinct clinical entities; however,
there is strong evidence that a defi nitive diagnosis of
the causes of neck pain is not possible in a clinical
setting. [66, 67] By using the term non-specific neck pain,
which encompasses many descriptors,  we have
addressed the clinical reality that patients presenting
with neck pain can have several concurrent sources of
pain from joints, muscles, and ligaments.
In addition to aggregating all included studies,
irrespective of diagnostic label, we also combined data
irrespective of the intended rationale for treatment, as
long as neck muscles and spinal joints were exposed to
laser irradiation. Transcutaneous application results in
laser-energy scattering and spreading into a threedimensional
volume of tissue, up to 5 cm for infrared
laser.  Since the same effect would be achieved with
application of laser energy to acupuncture points, we also
included data from studies in which local points in the
neck were treated as part of the protocol. Evidence suggests
that trigger points in the neck coincide with the location of
acupuncture points in 70–90% of patients (eg, BL10, GB
20, GB21, and Ah Shi points). [69, 70] Since trigger points and
acupuncture points are characterised by tenderness, the
treatment effect of laser irradiation to tender points,
trigger points, or acupuncture points is likely to be the
same. We did not distinguish any differences in subgroup
analyses between these techniques. Thus, when treating
neck pain with LLLT, irradiation of known trigger points,
acupuncture points, tender points, and symptomatic
zygapophyseal joints is advisable.
Dose assessment is crucial for interpretation of
outcomes of LLLT studies, for which failure to achieve a
dose in the recommended range has been identified as a
major factor for negative outcomes.  The direct relation
between positive outcomes of trials with adequate doses
of laser irradiation for the appropriate condition has been
shown in acute injury and soft-tissue inflammation, 
tendinopathies,  rheumatoid arthritis,  lateral
epicondylitis,  and osteoarthritis. 
Several crucial parameters of laser devices are needed
to assess dose of laser irradiation, but these doses were
inconsistently reported in the studies that we reviewed.
No study provided all parameters identified as important
by the scientific Committee of the World Association of
Laser Therapy.  In neck pain, however, there is little
reason to believe that factors other than a plausible
anatomical target, dose per point, and irradiation times
are essential for efficacy of class 3B lasers (5–500 mW).
We had sufficient data relating to each of these
components of therapy, when combined with
manufacturers’ specifications, to identify a dose-response
pattern for the number of joules per point and wavelength
used and positive outcome.
Subgrouping of studies by
wavelength and ascending doses reduced apparent
heterogeneity in treatment protocols and laser
parameters, and showed a dose-response pattern with
distinct wavelength-specific therapeutic windows. Most
statistical heterogeneity disappeared when we excluded
trials with small doses or flaws in treatment procedure
from efficacy analyses. Additionally, a very high dose
(54 J) of 830 nm LLLT used in one trial did not cause
beneficial nor harmful effects.  This finding suggests not
only that doses of this magnitude are higher than the
therapeutic window, but also that LLLT is safe even if
such an overdose is delivered. Frequency of treatments
varied from daily to twice a week, raising questions about
optimum treatment frequency.
Our analysis suggests that the optimum mean dose per
point for 820–830 nm was 5·9 J, with an irradiation time
of 39·8 s, and for 904 nm, 2·2 J delivered with an
irradiation time of 238 s. We recommend a multicentre,
pragmatic trial in an appropriately powered study to test
the effectiveness of parameters of this order, with both
pain intensity and functional improvement as outcome
Data from seven trials were available for up to 22 weeks
after the end of treatment, suggesting that positive effects
were maintained for up to 3 months after treatment
ended. Trials of knee osteoarthritis,  tendinopathies, [61, 76 ]
and low back pain reported similar longlasting effects of
LLLT. [77, 78] These results contrast with those for nonsteroidal
anti-inflammatory drugs in arthritis and spinal
disorders, for which the effect ends rapidly when drug
use is discontinued.  Reduction of chronic neck pain at
the end of treatment of 19·86 mm and at follow-up of
23·44 mm on a visual analogue scale of 100 mm
represents clinically Significant pain relief. [64, 65] This result
compares favourably with those of pharmacological
therapies that are widely used in treatment of neck pain,
for which investigators have shown no conclusive
evidence of benefit.  Intake of oral analgesic drugs was
not systematically reported; however, randomisation
within trials would keep the confounding effect of this
factor to a minimum.
Half the studies obtained data for side-effects, [39, 42, 44–46, 49, 52, 53]
with tiredness reported in the laser-treated group in
three studies, [42, 46, 49] which was Significant in one study.  Since LLLT does not generate destructive heat, safety
relates mainly to potential eye damage, dependent on
class of laser device (classes 1–4), which is defi ned by
analysis of several parameters. Safety glasses are
required for classes 3B and 4 to eliminate this risk, and
would be required for use in all studies. Systematic
reporting of side-effects in future studies would also be
recommended to clarify short-term and long-term safety
aspects of LLLT.
Mechanisms for LLLT-mediated pain relief are not fully
understood. Several investigations exploring the
pleiomorphic tissue effects of laser irradiation provide
plausible explanations for the clinical effects of LLLT.
Anti-inflammatory effects of red and infrared laser
irradiation have been shown by reduction in specific
inflammatory markers (prostaglandin E2, interleukin 1β,
tumour necrosis factor α), in in-vitro and in-vivo animal
studies and in man.  In animal studies, the antiinflammatory effects of LLLT are similar to those of
pharmacological agents such as celecoxib,  meloxicam, 
diclofenac,  and dexamethasone. 
Chronic neck pain is
often associated with osteoarthritis of zygapophyseal
joints,  which is manifested by pain, swelling, and
restricted movement as clinical markers of local
infl ammation. Laser-mediated anti-inflammatory effects
at this joint could result in decreased pain and increased
mobility. The distance between skin surface and lateral
aspect of the facet joint is typically 1·5–3·0 cm without
pressure, and less with contact pressure (measured with
ultrasonography [unpublished data, JMB]). Since 830 nm
and 904 nm lasers penetrate to several centimetres, [24, 84]
anti-inflammatory effects at zygapophyseal joints are a
plausible mechanism of pain relief.
Another possible mechanism of LLLT action on muscle
tissue is a newly discovered ability to reduce oxidative
stress and skeletal muscle fatigue with doses similar to
those delivering anti-inflammatory effects. This effect
has been reported in an animal study  and in human
studies with biceps humeri contractions and different
wavelengths. [86, 87] Because muscle fatigue is usually a
precursor of muscle pain, and chronic trapezius myalgia
is associated with increased electromyograph activity
during contractions and impaired microcirculation, 
reduction of oxidative stress and muscular fatigue could
be beneficial in patients with acute or chronic neck
Inhibition of transmission at the neuromuscular
junction could provide yet another mechanism for LLLT
effects on myofascial pain and trigger points. [89, 90] Such
effects could mediate the clinical finding that LLLT
decreases tenderness in trigger points within 15 min of
application.  Laser-induced neural blockade is a further
potential mechanism for the pain-relieving effects of
LLLT. [92, 93] Selective inhibition of nerve conduction has
been shown in Aδ and C fibres, which convey nociceptive
stimulation. [94, 95] These inhibitory effects could be mediated
by disruption to fast axonal flow in neurons  or inhibition
of neural enzymes. 
These tissue effects of laser irradiation might account
for the broad range of conditions that are amenable to
LLLT treatment. Whether specific treatment protocols are
necessary to elicit different biological mechanisms is
unknown. Heterogeneity of treatment protocols might be
due partly to variation in LLLT parameters and protocols,
eliciting different effects. Whatever the mechanism of
action, clinical benefits of LLLT occur both when LLLT is
used as monotherapy [13, 43] and in the context of a regular
exercise and stretching programme. [46, 47] In clinical settings,
combination with an exercise programme is probably
preferable. The results of LLLT in this review compare
favourably with other widely used therapies, and especially
with pharmacological inter ventions, for which evidence
is sparse and side-effects are common. [16, 32]
RTC participated in the literature search, development of inclusion and
exclusion criteria, selection of trials for inclusion in the analysis,
methodological assessment, data extraction and interpretation, and
writing of the report. MIJ participated in data analysis and interpretation,
critically reviewed the report with special expertise in pain management,
and contributed to writing of the report. RABL-M participated in data
interpretation and analysis, and critically reviewed the report with respect
to the mechanism of action of laser, and relevance to neck pain.
JMB participated in development of inclusion and exclusion criteria,
translation of non-English language articles, methodological assessment,
data analysis and interpretation, writing of the results section of the
report, and supervised writing of the report as a whole.
Conflicts of interest
RTC is a member of the World Association for Laser Therapy (WALT),
the Australian Medical Acupuncture College, the British Medical
Acupuncture Society, the Australian Pain Society, the Australian
Medical Association, and the Royal Australian College of General
Practitioners. MIJ is a member of the International Association of the
Study of Pain. RABL-M is funded by Fundação de Amparo do Estado
de São Paulo (FAPESP, Brazil) and is scientific secretary of WALT,
from which he has never received funding, grants, or fees. JMB is a
member of the Norwegian Physiotherapy Association, Norwegian
Sports Physiotherapy Society, Norwegian Society for Rheumatological
and Orthopedic Physiotherapy, and has received research awards and
grants from the Norwegian Manual Therapy Association, the
Norwegian Neck and Back Congress, the Norwegian Research Council,
the Norwegian Fund for Postgraduate Training in Physiotherapy, and
the Grieg Foundation. He is also president of WALT, a position for
which he has never received funding, grants, or fees.
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