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Comparison of atlanto-axial artery hemodynamics during cervical spine manipulation with doppler ultrasound in rhesus macaques

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Background: The vulnerability of atlanto-axial vertebral artery (C1-C2 VA) to cervical spine manipulation (CSM), resulting in compromised blood flow and possible cerebrovascular accident, is well recognized. It needs to build animal model for further investigate the blood flow changes in the vertebral arteries during cervical spine manipulation (CSM). Methods: Peak systolic velocity (PSV), end diastolic velocity (EDV), resistance index (RI) and lumen diameter of bilateral VAs were measured using duplex Doppler ultrasound in 6 healthy rhesus monkeys with the cervical spine in eight cervical positions used in CSM. Results: The mean PSV and EDV of both VAs were decreased significantly in contralateral rotation, extension-ipsilateral and -contralateral rotation, and extensionipsilateral and -contralateral rotation with traction (P < 0.05). A significant increase (P < 0.05) in RIs with left rotation and extension-left rotation-traction was demonstrated in right VA. Doppler waveforms revealed that blood flow followed a dampened systolic waveform during contralateral rotation and extension-contralateral rotation, and a near occlusion in combined extension-contralateral rotation with traction. Conclusion: The VA of rhesus monkey is subjected to forces that are sufficient to reduce blood flow velocity in positions involving in contralateral rotation, extension-ipsilateral and -contralateral rotations as well as combined extension- rotation with manual traction. The study of hemodynamics of the vertebral artery in rhesus monkey, which apply to biologic and mechanical research, is need to further conduct.
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Int J Clin Exp Med 2016;9(1):209-218
www.ijcem.com /ISSN:1940-5901/IJCEM0015739
Original Article
Comparison of atlanto-axial artery hemodynamics
during cervical spine manipulation with doppler
ultrasound in rhesus macaques
Kai-Qi Cui1,3*, Yuan Jiang1,3*, Yuan-Yi Zheng2, Xiao Zheng2, Ze-Sha Ling1,3, Gong-Wei Jia1, Lang Jia1, Wei
Jiang1, Le-Hua Yu1,3
1Department of Rehabilitation Medicine and Physical Therapy, The Second Afliated Hospital of Chongqing Medi-
cal University, Chongqing, P. R. China; 2Department of Ultrasonography, The Second Afliated Hospital of Chongq-
ing Medical University, Chongqing, P. R. China; 3School of Rehabilitation Medicine and Physical Therapy, Chongq-
ing Medical University, Chongqing, P. R. China. *Co-rst authors.
Received September 7, 2015; Accepted November 23, 2015; Epub January 15, 2016; Published January 30,
2016
Abstract: Background: The vulnerability of atlanto-axial vertebral artery (C1-C2 VA) to cervical spine manipulation
(CSM), resulting in compromised blood ow and possible cerebrovascular accident, is well recognized. It needs to
build animal model for further investigate the blood ow changes in the vertebral arteries during cervical spine
manipulation (CSM). Methods: Peak systolic velocity (PSV), end diastolic velocity (EDV), resistance index (RI) and
lumen diameter of bilateral VAs were measured using duplex Doppler ultrasound in 6 healthy rhesus monkeys
with the cervical spine in eight cervical positions used in CSM. Results: The mean PSV and EDV of both VAs were
decreased signicantly in contralateral rotation, extension-ipsilateral and -contralateral rotation, and extension-
ipsilateral and -contralateral rotation with traction (P < 0.05). A signicant increase (P < 0.05) in RIs with left rota-
tion and extension-left rotation-traction was demonstrated in right VA. Doppler waveforms revealed that blood ow
followed a dampened systolic waveform during contralateral rotation and extension-contralateral rotation, and a
near occlusion in combined extension-contralateral rotation with traction. Conclusion: The VA of rhesus monkey is
subjected to forces that are sufcient to reduce blood ow velocity in positions involving in contralateral rotation,
extension-ipsilateral and -contralateral rotations as well as combined extension- rotation with manual traction. The
study of hemodynamics of the vertebral artery in rhesus monkey, which apply to biologic and mechanical research,
is need to further conduct.
Keywords: Atlanto-axial joint, vertebral artery, Doppler ultrasound, rhesus macaques
Introduction
Cervical spine manipulation (CSM) is a thera-
peutic intervention and has increasingly admin-
istrated by physicians, physical therapists, and
chiropractors around the world [1-6]. Some evi-
dence in literature reviews to support the use
of manipulation techniques for the treatment of
neck pain and headache [7-11]. A conservative
estimate of approximately 193 million of CSMs
is performed each year in the United States
and Canada [5-12]. This growing acceptance
has, in turn, advocated the necessity to evalu-
ate its potential side effects and complications
that include cerebrovascular accidents such as
stroke, paralysis, and even death [13-17], most
commonly due to arterial dissection of the ver-
tebral artery (VA) at atlanto-axial joint (C1-C2)
[18-20]. It is estimated that the incidence of
vertebral artery dissection (VAD) ranges from 1
to 1.7 in 100,000 person years in the United
States [21], and the stoke resulting from VAD
happened in 0.75 to 1.12 per 100,000 person
years [22]. Despite this relatively rare occur-
rence, the clinical relevance of changes in VA
blood ow associated with cervical spine move-
ments have been the main focus of consider-
able researches.
Several studies were conducted that measure
VA blood ow velocity using Doppler ultrasonog-
raphy. However, the results of such studies
have provided conicting evidence, for instance,
some studies suggested that there was dimin-
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
210 Int J Clin Exp Med 2016;9(1):209-218
ished blood ow in the contralateral VA during
cervical rotation whether extension was added
or not [23, 24], whereas other authors have
reported that ow velocity in VAs decreased sig-
nicantly during both ipsilateral and contralat-
eral rotation [25-27], or no changes [28-30].
Research ndings for the sustained extension-
rotation are equally equivocal with signicant
decreases in blood ow [31, 32], or no effect
noted on VA blood ow [25, 27]. In addition,
other positions such as extension and the
application of manual traction have been limit-
edly investigated with no consensus conclusion
on the ndings [24, 27, 31].
On the basis of the inconsistency of the evi-
dence, it is need to develop experimental ani-
mal model for investigate the blood ow chang-
es in the vertebral arteries during cervical
spinal manipulation or/and pre-manipulative
testing of these vessels, for instance, clinical
studies are usually complicated by uncontrolled
variables such as age, gender, nutrition, hyper-
tension, alcohol, tobacco, and drug abuse, data
derived from clinical trials measuring blood ow
velocity are difcult to interpret and generally
require large sample size for relevant informa-
tion [33, 34]. To investigate whether end-range
cervical movements produce signicant chang-
es in VA blood ow velocity, resistance index,
and lumen diameter, the rhesus macaque
(Macaca mulatta), a member of the Old-world
Primate, was selected as the study subject to
provide some evidence on which to base the
treatment of humans.
Materials and methods
Animals
A total of 6 adult rhesus macaques, 3 male, 3
female, approximate age 4.3 ± 0.6 yrs.; weight
4.5 ± 0.6 kg; height 51.5 ± 2.1 cm (Macaca
mulatta, Chongqing Medical University Animal
Research Center, Chongqing, P. R. China) were
involved in the current study. All experimental
protocol was approved by the Institutional
Animal Care and Use Committee of Chongqing
Medical University. Before participation in the
experimental study all animals underwent a
routine physical examination, ensured they are
one group of healthy rhesus macaques without
any neurological, cardiovascular and musculo-
skeletal diseases. A prior Doppler examination
ensured that there was no any abnormality in
cervical spine and neck vasculature. Animals
were singled-housed in cages (121 × 68 × 81
cm) located in a clean and quiet single room.
The lights were on 12 hours daily from 7:00 am
to 7:00 pm, and the temperature was main-
tained at 22°C. A pelleted diet was fed twice
daily (Lab Diet, Chongqing, P. R. China) with
fresh fruits/vegetables, and water was avail-
able ad libitum.
Pre-test preparation
All rhesus monkeys were intramuscularly anes-
thetized with Xylazine Hydrochloride (0.1 mL/
kg) and handled humanely for all procedures.
Postoperative analgesia with Buprenorphine
Hydrochloride (0.1 mg/kg) was given as need-
ed. Postoperative evaluations for behaviors,
food and water consumption, and urine and
feces production were done. Under sterile cir-
cumstances the rhesus monkey were placed in
supine position on an insulating mat, and the
region of interest was washed and cleaned
accordingly. A thorough examination of the cer-
vical spine was performed prior to the Doppler
test.
Cervical spine manipulation maneuvers
Eight spinal manipulation maneuvers were cho-
sen that incorporate all of the maximum pas-
sive arthrokinematic facet motions and per-
formed bilaterally with the animal placed in
supine position. All cervical movements were
performed by a single qualied physical thera-
pist with extensive experience in manual thera-
py and joint manipulation. The procedure com-
menced with a 10 minutes rest period to allow
for a period of hemodynamic stability. Systolic
blood pressure (SBP, mmHg), diastolic blood
pressure (DBP, mmHg) and pulse rate (PR,
beats/min) were measured in the resting posi-
tion and during cervical manipulations with a
digital Blood Pressure Monitor (model DS-145,
ALPK2, Japan; ± 3 mmHg for BP and ± 5% for
PR). Eight spinal manipulation maneuvers as
follow:
Flexion 60o
For the C1-C2 facet joint exion shown in Figure
1B, the examiner manually stabilized C1 with a
bilateral laminar contact between the thumb
and index nger of the stabilizing hand while
placing the manipulating hand against the infe-
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
211 Int J Clin Exp Med 2016;9(1):209-218
rior nuchal line, and then passively introduced
exion to 60o.
Extension 60o
With the animal’s head extending over the edge
of the examination table, the examiner manu-
ally stabilized C1 with a bilateral laminar con-
tact between the thumb and index nger of the
stabilizing hand while placing the manipulating
hand against the inferior nuchal line, and then
passively introduced extension to 60o (Figure
1C).
Rotation 90o
The examiner encircled the animal’s head, with
index nger on the ipsilateral lamina of C1,
Figure 1. Cervical positions of rhesus macaque during duplex Doppler ultrasound examination.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
212 Int J Clin Exp Med 2016;9(1):209-218
spanned the arch of C2 with the thumb and
passively introduced 90o rotation either away
from the US evaluation side or toward the US
evaluation side (Figure 1D, 1G).
Extension 60o and rotation 90o
With the animal’s head extending over the
examination table, C1 was rst passively pre-
positioned in 60o extension, and then was
either 90o rotated away from the US evaluation
side or rotated toward the US evaluation side
(Figure 1E, 1H).
Extension 60o, rotation 90o and traction
For the C1-C2 facet joint distraction, C1 was
rst passively pre-positioned with a combina-
tion of 60o extension and 90o rotation either
away from the US evaluation side or rotation
toward the US evaluation side; then the exam-
iner passively distracted C1 with approximately
1/3 the animal’s body weight to achieve 1-2
mm of vertebral separation in a cranial direc-
tion (Figure 1F, 1I).
Ultrasonographic examination
A standard, duplex Doppler ultrasound device
(Mylab 50, Esaoto Corporation, Genoa, Italy)
was applied to measure peak systolic velocity
(PSV, cm/s), end diastolic velocity (EDV, cm/s),
resistance index (RI) and lumen diameters (LD,
cm). The machine possesses a color ow map-
ping capability, and a high frequency 12-5 MHz
broadband linear array transducer. All scanning
was performed by a single qualied ultrasonog-
rapher with extensive experience in musculo-
skeletal US imaging and the examination of the
extra-cranial vasculature. Measurement of
PSV, EDV, RI and LD were recorded three times
in each position for both left and right VAs using
the same order of sampling. Each of the posi-
tions was sustained passively for at least 30
seconds. Ranges of motion (ROM, degree) for
exion, extension and left/right rotation were
measured with a goniometer. The animal was
then rested in a neutral position for 10 seconds
and was observed for neurological signs before
re-positioning for the next movement. Following
the test procedure, the ultrasonographer
reviewed all scans for any artery pathology or
abnormal discrepancy.
Statistical analysis
The software package SPSS version 20.0
(SPSS Inc., Chicago, Illinois, USA) was used for
statistical analysis. The mean (± SD) blood ow
PSVs and EDVs, RIs, and LDs were calculated
for the right and left VA with the cervical spine
in all the different positions. Hemodynamic sta-
bility was evaluated by comparing SBP, DBP,
and PR measurements taken before and during
the ultrasound examination, using paired sam-
ples t-tests. The consistency between mea-
surements of ROM was also determined using
paired samples t-test. One-way ANOVA with
repeated measures on the PSV, EDV, RI, and LD
measurements were performed to identify any
statistically signicant change between the
neural position and each different head move-
ment. Post hoc tests were calculated with
Table 1. Values of blood ow velocities and lumen diameters taken at the C1-C2 region of the right
and left vertebral artery in rhesus monkeys
Position PSV-LVA
(cm/s)
PSV-RVA
(cm/s)
EDV-LVA
(cm/s)
EDV-RVA
(cm/s) RI-LVA RI-RVA LD-LVA
(cm)
LD-RVA
(cm)
N 16.71 ± 3.21 16.65 ± 5.45 7.43 ± 2.03 7.77 ± 2.16 0.56 ± 0.07 0.52 ± 0.08 0.10 ± 0.01 0.11 ± 0.02
F 14.24 ± 0.84 13.45 ± 1.25 5.70 ± 0.21 5.27 ± 1.35 0.60 ± 0.02 0.61 ± 0.09 0.08 ± 0.01 0.10 ± 0.01
E 14.69 ± 2.73 14.56 ± 2.76 5.42 ± 3.77 6.37 ± 3.77 0.66 ± 0.17 0.58 ± 0.15 0.11 ± 0.01 0.10 ± 0.01
LR 14.51 ± 1.86 11.90 ± 3.43*5.93 ± 1.38 4.02 ± 1.34*0.60 ± 0.09 0.65 ± 0.12*0.11 ± 0.01 0.10 ± 0.02
RR 10.38 ± 1.15*14.88 ± 4.00 4.50 ±0.83*6.10 ± 1.56 0.57 ± 0.05 0.58 ± 0.04 0.10 ± 0.02 0.10 ± 0.01
ELR 10.67 ± 1.09*11.07 ± 0.87*4.54 ± 1.33*4.86 ± 0.97*0.58 ± 0.11 0.56 ± 0.08 0.10 ± 0.02 0.10 ± 0.02
ERR 9.75 ± 1.79*11.6 ± 2.55*4.02 ± 0.77*5.91 ± 1.93 0.59 ± 0.03 0.51 ± 0.07 0.10 ± 0.02 0.10 ± 0.02
ELRT 10.47 ± 2.30*9.48 ± 1.28*4.20 ± 1.68*3.03 ± 0.72*0.61 ± 0.10 0.68 ± 0.09*0.11 ± 0.02 0.10 ± 0.02
ERRT 9.49 ± 1.26*10.96 ± 2.93*3.19 ± 1.24*4.22 ± 1.35*0.66 ± 0.11 0.62 ± 0.07 0.10 ± 0.01 0.11 ± 0.01
Abbreviations: PSV-peak systolic velocity; EDV-end diastolic velocity; RI-resistive index; LD-lumen diameter; LVA-left vertebral artery; RVA- right
vertebral artery. N-neutral; F-exion; E-extension; LR-left rotation; RR- right rotation; ELR-extension-left rotation; ERR-extension-right rotation; ELRT-
extension-left rotation-traction; ERRT- extension-right rotation-traction. All values are mean ± standard deviation, n = 6 rhesus macaque monkeys,
*P < 0.05.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
213 Int J Clin Exp Med 2016;9(1):209-218
Bonferroni correction for multiple comparisons
(P < 0.05). One additional paired sample t-tests
was used to identify any signicant hemody-
namic difference (P < 0.05) between the left
and right VA in each different position. P values
< 0.05 were considered to indicate a trend
towardstatistical signicance.
Results
Ultrasonographic examination was successful-
ly performed in all positions on both left VA
(LVA) and right VA (RVA). No animal showed any
alteration in BP, PR, and ROM as a result of the
experimental procedure that was statistically
signicant in relation to the ndings of this
study. No abnormalities were reported by the
ultrasonographer upon reviewing the ultra-
sound scans.
Comparison of VA blood ow in various cervi-
cal positions
The mean (± SD) blood ow PSVs, EDVs, RIs as
well as LDs for neutral and each of different
cervical spine positions are shown in Table 1.
Typical patterns of change in blood ow for both
VAs are illustrated in Figure 2. The mean PSV of
LVAs tended to decrease signicantly in sus-
tained contralateral rotation (RR) (P < 0.05),
extension -left/right rotation (ELR, ERR) (P <
0.01), and extension-left/right rotation with the
application of traction (ELRT, ERRT) (P < 0.01).
The similar patterns of change was also found
in RVA, a signicant decrease in blood ow
velocities with contralateral cervical spine rota-
tion (LR) (P = 0.01), ELR and ERR (P < 0.05),
ELRT and ERRT (P < 0.01) (Figure 2A). The
mean EDV of LVAs and RVAs decreased signi-
cantly during contralateral rotation (P < 0.05),
ELR and ERR (P < 0.05), ELRT and ERRT (P <
0.01) as compared with the neutral position
(Figure 2B). A signicant increase in RIs with
left rotation (LR) (P < 0.05) and extension-left
rotation-traction (ELRT) was demonstrated in
RVAs (P = 0.003). For the LVA there were similar
changes in the RIs, but were not signicant
(Figure 2C).
Comparison of VA blood ow between left and
right VAs
On comparing the mean PSVs between the left
and right VAs with the cervical spine in neutral
position, no statistically signicant difference
Figure 2. Changes in A. Mean peak systolic velocity (PSV); B. Mean end diastolic velocity (EDV); C. Mean resistance
index (RI); and D. Mean lumen diameter (LD) of left and right vertebral artery in rhesus monkeys. *P<0.05 in LVA;
oP < 0.05 in RVA.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
214 Int J Clin Exp Med 2016;9(1):209-218
was found between LVA and RVA (P = 0.769)
and during the positioning sequence (P =
0.290). The similar no signicant difference
was also found between the mean EDVs of LVA
and RVA in neutral position (P = 0.164) and in
each different position (P = 0.262). RIs of LVA
were not statistically different from RVA in neu-
tral cervical spine position (P = 0.329) and no
signicant differences (P = 0.307) in each cer-
vical position. In addition, no signicant differ-
ence was found in the mean lumen diameters
between the left and right sides in neutral posi-
tion (P = 0.222) and during different cervical
movements (P = 0.551).
Doppler waveforms of blood ow
Upon reviewing spectral Doppler waveforms of
blood ow velocity measurements, the results
revealed that blood ow followed a low resis-
tance pattern in the neutral position, which is a
wide peak systolic and high diastolic ow in the
VA (Figure 3A); a dampened systolic waveform,
which is an indication of a turbulence distal to
the point of sampling during positions such as
end-range contralateral rotation and extension-
contralateral rotation (Figure 3B, 3C); then the
waveform indicated a near occlusion in com-
bined extension-contralateral rotation with
traction, where blood ow velocity was slower
than the usual ow velocity in the neutral posi-
tion, and diastolic ow velocity reached zero
and extended beyond the baseline (Figure 3D).
Discussion
CSM can ease the neck pain and headache,
however, it could cause some iatrogenic dam-
ages. Although the probability of the iatrogenic
damages is very low, the adverse effect will be
great in some case. Atlanto-axial joint is the
most agility and weakest as well as the most
dangerous movement segment as it has com-
plex structures and special functions in occipi-
to-cervical migration department. The charac-
teristic of rotary motion of atlanto-axial joint
initiated from atlas: 1) rotary motion from 0° to
30°, the axis remains immovable; 2) rotary
motion from 30° to 60°, the axis begins move,
but at a slower speed compared with atlas; 3)
rotary motion from 60° to maximumrotation,
rotation of atlas and axis have reached to maxi-
Figure 3. Ultrasound spectral images of blood ow velocities during different head positions.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
215 Int J Clin Exp Med 2016;9(1):209-218
mum, the rotation of the neck occurs exclusive-
ly at segments below the axis. The segment of
VAs adjacent to atlanto-axial joint is considered
to be the most vulnerable to the stimuli to cervi-
cal vertebra, such as rotation, stretch and com-
pression [35]. Sim et al. [36] suggested that
the VA is elongated by approximately 5 mm dur-
ing contralateral rotation with 50-90% of cervi-
cal rotation attributed to movement at the
atlanto-axial joint. Therefore, the adversely
inuence of intracranial blood ow would occur-
rence during CSM, even likely deteriorate the
symptom of verterbral-basilar artery ischemia,
particularly if atherosclerosis or other vascular
disorders simultaneous in VAs.
Recently, some scholars suggested that many
of side effects (vertebral artery dissection,
stroke, etc.) are unlikely to be the result of cer-
vical manipulation. Even a drastic debate
between David Cassidy and Benedict, argued
whether abandon CSM for security reasons [37,
38]. It was documented that CSM is safe for
normal and healthy VAs from a mechanical
point [39]. Healthy adults who experience vari-
ous head positions and CSM have no signi-
cant change in blood ow in the VAs using
Duplex ultrasound with colour Doppler imaging
[40]. Another research measured blood ow
and velocity at the atlanto-axial artery using
phase-contrast magnetic resonance imaging,
and no signicant change in blood ow have
been found [41]. However, those results are
inconsistent with previous study [26]. By the
way, the relationship between vertebral artery
lesion and CSM in humans is still difcult con-
rm as the integrity of vessel is typically
unknown before using CSM. Some scholars
focus on using animals to study the changes in
VA blood ow associated with cervical spine
movements or simulating a pre-existing vascu-
lar lesion within the VAs of animals prior to CSM
application [42-44]. Comparison with adult pigs
or dogs, rhesus monkey as a kind of non-human
primates has the unique dominant position
depend upon genetic and genomic similarity,
anatomic and physiologic closeness to humans
[45, 46]. Moreover, the 3D-CTA imaging data of
cervical artery of rhesus monkeys, which was
obtained from our prior subject, shown that ver-
tebral artery of rhesus monkey was similar with
anatomic structure of human. We speculate
this investigation of atlanto-axial artery in rhe-
sus monkey would have been capable of pro-
viding quantify VAs hemodynamics during CSM.
The ndings of this present study demonstrat-
ed that the blood ow of the VAs of rhesus
macaque was signicantly affected by cervical
positions especially involving with contralateral
rotation, extension-rotation and a combined
extension-rotation with manual traction.
However, there was no signicant reduction in
blood ow during exion and extension of the
cervical spine. Variations in BP and PR were
unlikely to contribute to the changes observed
because these measurements were not signi-
cantly different in each different cervical posi-
tion. Based on the anatomic structures with
regard to the cervical arteries, the sustained
rotation and extension-rotation tests have
been clinically used to determine the presence
of vertebrobasilar artery dysfunction. We found
that full range of cervical rotation at C1-C2
stressed the VAs sufciently to demonstrate
reduction of blood ow. Although no signicant
difference was found between the diameters of
the left and right VAs in either the neutral posi-
tion or cervical spine rotation, mean PSV and
EDV tended to decrease below resting values in
the both left and right VAs during contralateral
rotation. Extension-rotation has also been
investigated extensively with controversial
results, and combined extension- rotation
mechanically stressed the contralateral artery
more than rotation alone. It is possible that
when attempting to combine full extension with
rotation, the vertebral artery is more vulnerable
to shear and tensile forces at the region, where
it exits C2 and runs vertically and laterally to
C1. Additional traction applied to the cervical
spine while it is in an extended and rotated
position produced the maximal mechanical
stress to the contralateral VA as compared to
any other position.
In addition, the RI increased signicantly in
right VA during left rotation and combined
extension-left rotation-traction, suggesting that
the resistance encountered by the blood ow
was actually increased. This nding was consis-
tent with the expectation of vessel narrowing
and associated increased resistance to ow.
The RI is based on the premise that diastolic
velocity is likely to be reduced to a greater
extent by higher resistance than is systolic
velocity, leading to a rise in the index [32].
However, the measurements of this study indi-
cate that both the PSVs and the EDVs of VAs
are reduced in these positions, albeit the PSVs
to a proportionally greater degree.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
216 Int J Clin Exp Med 2016;9(1):209-218
Limitations
As with any study, there are a number of limita-
tions in the current study. First of all, the study
is based on maneuvers of cervical spine manip-
ulation, the order of movement progression
was the same for all animals. This method was
chosen in order to gradually adding further
stress to the arterial system. However, because
combined extension-rotation-traction was the
last movements in the sequence and demon-
strated the greatest ow decrease, it is not
completely clear if the order of testing may
have affected the results and further investiga-
tion is required before such claims can be justi-
ed. Also, a convenience sample of young,
healthy, and asymptomatic monkeys was used
in this study. Since no attempt was made to
investigate whether positional maneuvers have
a greater hemodynamic effect in those mon-
keys with symptomatic vertebrobasilar insuf-
ciency, it is therefore not possible to generalize
the results to the symptomatic population. In
addition, although Doppler ultrasound has
advantages in terms of patient comfort, non-
invasiveness and relative time of performance
in comparison to angiography, there are a num-
ber of potential problems associated with its
use. For instance, the reliability of Doppler sam-
pling is highly dependent on the skill of the
technician to accurately locate and identify the
VA, particularly when measuring in the extreme
neck positions such as combined extension
and rotation. Another major shortcoming of
ultrasound is the lack of specicity, ultrasound
often shows nonspecic hemodynamics signs
of VA occlusion.
Conclusions
On the basis of the reference data presented in
this study, the VA of rhesus monkey was sub-
jected to forces that was sufcient to reduce
blood ow velocity in positions involving in con-
tralateral rotation, combined extension with
ipsilateral and contralateral rotations, and
combined extension-rotation with manual trac-
tion of the cervical spine seems to have a par-
ticularly signicant effect in reducing the maxi-
mum blood ow in the contralateral VA. Given
the comparison with the recently research of
atlanto-axial artery hemodynamics during CSM
in healthy human from other scholars [39, 40],
the different results between rhesus monkey
and humans implicate that furtherbiologic and
mechanical research of vertebral artery in rhe-
sus monkey need to investigate, even though
rhesus monkey has lots of similarities in ana-
tomic structure of vertebral artery.
Acknowledgements
This research received nancial support from
National Natural Science Foundation of China,
No: 81171859 and Chongqing Municipal
Healthcare Department Medical Research
Grant, No. 2010-1-20: 2. We also express our
sincere thanks to Dr. Yi Yuan, Dr. Lei Yuan
and Miss Zunzhen Zhou for their helpful
assistance.
Disclosure of conict of interest
None.
Address correspondence to: Dr. Le-Hua Yu, Depar t-
ment of Rehabilitation Medicine and Physical Ther-
apy, The Second Afliated Hospital of Chongqing
Medical University, Chongqing, P. R. China; School of
Rehabilitation Medicine and Physical Therapy,
Chongqing Medical University, Chongqing, P. R.
China. Tel: +86 13896179179; E-mail: yulehua@
cqmu.edu.cn
References
[1] Cassidy JD, Lopes AA, Yong-Hing K. The imme-
diate effect of manipulation versus mobiliza-
tion on pain and range of motion in the cervi-
cal spine: A randomized controlled trail. J
Manipulative Physiol Ther 1992; 15: 570-575.
[2] Koes BW, Bouter LM, van Mameren H, Essers
AH, Verstegen GM, Hofhuizen DM, Houben JP,
Knipschild PG. The effectiveness of manual
therapy, physiotherapy, and treatment by the
general practitioner for nonspecic back and
neck complaints, a randomized clinical trail.
Spine 1992; 27: 28-35.
[3] Koes BW, Bouter LM, van Marmeren H, Essers
AH, Verstegen GJ, Hofhuizen DM, Houben JP,
Knipschild PG. A randomized clinical trail of
manual therapy and physiotherapy for persis-
tent neck and back complaints: Sub-group
analysis and relationship between outcome
measures. J Manipulative Physiol Ther 1993;
16: 211-219.
[4] Gross AR, Aker PD, Goldsmith CH, Peloso P.
Conservative management of mechanical
neck disorders: A systematic overview and
meta-analysis. Online J Curr Clin Trails 1996;
200-201.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
217 Int J Clin Exp Med 2016;9(1):209-218
[5] Hurwitz EL, Aker PD, Adams AH, Meeker WC,
Shekelle PG. Manipulation and mobilization of
the cervical spine: a systematic review of the
literature. Spine 1996; 21: 1746-1759, discus-
sion 1759-1760.
[6] Bronfort G, Assendelft WJ, Evans R, Haas M,
Bouter L. Efcacy of spinal manipulation for
chronic headache: a systematic review. J Ma-
nipulative Physiol Ther 2001; 27: 457-466.
[7] Vernon H, McDermaid CS, Hagino C. System-
atic reviewof randomized clinical trials of com-
plementary/alternative therapies in the treat-
ment of tension-type and cervicogenic
headache. Complement Ther Med 1999; 7:
142-55.
[8] Vernon H, Humphreys K, Hagino C. Chronic
mechanical neck pain in adults treated by
manual therapy: a systematic review of change
scores in randomized clinical trials. J Manipu-
lative Physiol Ther 2007; 30: 473-8.
[9] Refshauge KM, Parry S, Shirley D, Larsen D,
Rivett DA, Boland R. Professional responsibility
in relation to cervical spine manipulation. Aust
J Physiother 2002; 48: 171-179.
[10] Bronfort G, Haas M, Evans RL, Bouter LM. Ef-
cacy of spinal manipulation and mobilization
for low back pain and neck pain: a systematic
review and best evidence synthesis. Spine
2004; 4: 335-356.
[11] Hurwitz EL, Carragee EJ, Van der Velde G, Car-
roll LJ, Nordin M, Guzman J, Peloso PM, Holm
LW, Côté P, Hogg-Johnson S, Cassidy JD, Halde-
man S; Bone Joint Decade 2000-2010 Task
Force on Neck Pain and Its Associated Disor-
ders. Treatment of neck pain: noninvasive in-
terventions: results of the Bone and Joint De-
cade 2000-2010 Task Force on neck pain and
its associated disorders. Spine 2008; 33:
S123-52.
[12] Haldeman S, Carey P, Townsend M, Papado-
poulos C. Arterial dissections following cervical
manipulation: the chiropractic experience.
CMAJ 2001; 165: 905-906.
[13] Di Fabio RP. Manipulation of the cervical spine:
risks and benets. Phys Ther 1999; 79: 50-65.
[14] Rivett DA, Sharples KJ, Milburn PD. Reliability
of ultrasonograpahic measurement of verte-
bral artery blood ow. NZ J Physiother 2003;
31: 119-128.
[15] Cagnie B, Vinck E, Beernaert A, Cambier D.
How common are side effects of spinal ma-
nipulation and can these side effects be pre-
dicted? Man Ther 2004; 9: 151-156.
[16] Hurwitz EL, Morgenstern H, Vassilaki M, Chi-
ang LM. Frequency and clinical predictors of
adverse reactions to chiropractic care in the
UCLA neck pain study. Spine (Phila Pa 1976)
2005; 30: 1477-1484.
[17] Sweeney A, Doody C. Manual therapy for the
cervical spine and reported adverse effects: A
survey of Irish manipulative physiotherapists.
Man Ther 2010; 15: 32-36.
[18] Grant R. Vertebral artery testing-the Australian
Physiotherapy Association Protocol after 6
years. Man Ther 1996; 1: 149-153.
[19] Kuether TA, Nesbit GM, Clark WM, Barnwell SL.
Rotational vertebral artery occlusion: A mecha-
nism of vertebrobasilar insufciency. Neuro-
surgery 1997; 41: 427-432.
[20] Haldeman S, Kohlbeck FJ, McGregor M. Risk
factors and precipitating neck movements
causing vertebrobasilar artery dissection after
cervical trauma and spinal manipulation.
Spine (Phila Pa 1976) 1999; 24: 785-794.
[21] Debette S, Leys D. Cervical-artery dissections:
predisposing factors, diagnosis andoutcome.
Lancet Neurol 2009; 8: 668-678.
[22] Boyle E, Côte P, Grier AR, Cassidy JD. Examin-
ing vertebrobasilar artery stroke in twoCanadi-
an provinces. J Manipulative Physiol Ther
2009; 32: S194-200.
[23] Refshauge KM. Rotation: A valid premanipula-
tive dizziness test? Does it predict safe manip-
ulation? J Manipulative Physiol Ther 1994; 17:
413-414.
[24] Mann T, Refshauge KM. Causes of complica-
tions from cervical spine manipulation. Aust J
Physiother 2001; 47: 255-256.
[25] Licht PB, Christensen HW, Hoilund-Carlsen PE.
Is there a role for premanipulative testing be-
fore cervical manipulation? J Manipulative
Physiol Ther 2000; 23: 175-179.
[26] Mitchell JA. Changes in vertebral artery blood
ow following normal rotation of the cervical
spine. J Manipulative Physiol Ther 2003; 26:
347-351.
[27] Arnold C, Bourassa R, Langer T, Stoneham G.
Doppler studies evaluating the effect of a phys-
ical therapy screening protocol on vertebral
artery blood ow. Man Ther 2004; 9: 13-21.
[28] Haynes M, Milne N. Color duplex sonographic
ndings in human vertebral arteries during
cervical rotation. J Clin Ultrasound 2001; 29:
14-24.
[29] Haynes MJ. Vertebral arteries and cervical
movement: Doppler ultrasound velocimetry for
screening before manipulation. J Manipulative
Physiol Ther 2002; 25: 556-567.
[30] Zaina C, Grant R, Johnson C, Dansie B, Taylor J,
Spyropolous P. The effect of cervical rotation
on blood ow in the contralateral vertebral ar-
tery. Man Ther 2003; 8: 103-109.
[31] Li YK, Zhang YK, Lu CM, Zhong SZ. Changes
and implications of blood ow velocity of the
vertebral artery during rotation and extension
of the head. J Manipulative Physiol Ther 1999;
22: 91-95.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
218 Int J Clin Exp Med 2016;9(1):209-218
[32] Rivett DA, Sharpless KJ, Milburn PD. Effect of
premanipulative tests on vertebral artery and
internal carotid artery blood ow: a pilot study.
J Manipulative Physiol Ther 1999; 22: 368-
375.
[33] Haldeman S, Kohlbeck FJ, McGregor M. Unpre-
dictability of cerebrovascular ischemia associ-
ated with cervical spine manipulation therapy:
a review of sixty-four cases after cervical spine
manipulation. Spine (Phila Pa 1976) 2002; 27:
49-55.
[34] Mitchell JA. Vertebral artery blood ow velocity
changes associated with cervical spine rota-
tion: a meta-analysis of the evidence with im-
plications for professional practice. J Man Ma-
nipulative Ther 2009; 17: 46-57.
[35] Cagnie B, Barbaix E, Vinck E, D’Herde K, Cam-
bier D. Atherosclerosis in the vertebral artery:
an intrinsic risk factor in the use of spinal ma-
nipulation? Surg Radiol Anat 2006; 28: 129-
134.
[36] Sim E, Vaccaro A, Berzlanovich A, Pienaar S.
The effecs of staged static cervcial exion-dis-
traction deformities on the patency of the ver-
tebral arterial vasculature. Spine 2000; 25:
2180-2186.
[37] Cassidy JD, Bronfort G, Hartvigsen J. Should
we abandon cervical spine manipulation for
mechanical neck pain? No. BMJ 2012; 344:
e3680.
[38] Wand BM, Heine PJ, O’Connell NE. Should we
abandon cervical spine manipulation for me-
chanical neck pain? Yes. BMJ 2012, 344:
e3679.
[39] Herzog W, Leonard TR, Symons B, Tang C,
Wuest S. Vertebral artery strains during high-
speed, low amplitude cervical spinal manipula-
tion. J Electromyogr Kinesiol 2012; 22: 740-
746.
[40] Bowler N, Shamley D, Davies R. The effect of a
simulated manipulation position on internal
carotid andvertebral artery blood ow in
healthy individuals. Man Ther 2011; 16: 87-
93.
[41] Quesnele JJ, Triano JJ, Noseworthy MD, Wells
GD. Changes in vertebral artery blood ow fol-
lowing various head positions and cervical
spine manipulation. J Manipulative Physiol
Ther 2014; 37: 22-31.
[42] Licht PB, Christensen HW, Svendensen P, Høi-
lund-Carlsen PF. Vertebral artery ow and cer-
vical manipulation: an experimental study. J
Manipulative Physiol Ther 1999; 22: 431-435.
[43] Kawchuk GN, Wynd S, Anderson T. Dening
the effect of cervical manipulation on vertebral
artery integrity: establishment of an animal
model. J Manipulative Physiol Ther 2004; 27:
539-546.
[44] Wynd S, Anderson T, Kawchuk G. Effect of cer-
vical spine manipulation on a pre-existing vas-
cular lesion within the canine vertebral artery.
Cerebrovasc Dis 2008; 26: 304-309.
[45] Bennett T, Abee CR, Hendrickson R. Nonhu-
man Primates in Biomedical Research. Ameri-
can College of Laboratory Animal Medicine
Series. San Diego: Academic Press; 1998.
[46] Abee CR, Manseld K, Tardif S, Morris T. Non-
human Primates in Biomedical Research: Vol-
ume 1: Biology and Management. Elsevier
Inc.; 2012.
Article
Instability of the cervical vertebrae and uncovertebral arthrosis are often the cause of hemodynamic disorders in the vertebral arteries. The aim of the investigation was to perform Doppler analysis of the parameters of blood flow in the vertebral arteries in patients with instability of the cervical spine (CS) and uncovertebral arthrosis with functional tests. Materials and methods. We examined 43 patients aged 18 to 44 years with CS instability, in 34 cases in combination with uncovertebral arthrosis (UVA). Determined Vs, Vd, RI, PI, MFV at the level in the second segment of the VA in the neutral position of the head and functional tests. Instability and uncovertebral arthrosis were diagnosed by radiography of the neck in frontal and lateral projections. Doppler sonography was performed on a Philips HD 11XE device using linear and microconvection sensors in the frequency range of 5-10 MHz Results. In patients with antilisthesis, the Vs value in the extension position was 32.1 ± 3.4 cm / s, RI - 0.71 ± 0.03, CCV - 84 ± 7 ml / min, significantly (P <0.05) lower than in the case of retrolisthesis and in comparison group (CG). With head flexion, the lowest Vs value was found in the group with retrolisthesis and was 31.5 ± 3.1 cm / s, RI – 0.72 ± 0.03, CCV – 87 ± 8 ml / min, significantly (P<0.05) lower than with antelisthesis and in CG. In the case of left localization of UVA, the lowest Vs value was recorded in the left VA during ipsilateral head rotation and amounted to 31.2 ± 2.9 cm / s, RI index - 0.72 ± 0.03, PI - 1.03 ± 0.06, and MFV - 85 ± 9 ml / min, reliably (P<0,05) are lower than the indices of the right VA with right-sided localization of UVA. In right-sided uncovertebral arthrosis, Vs in the right VA had the smallest value and amounted to 30.4 ± 3.2 cm / s, RI index - 0.73 ± 0.03, PI - 1.04 ± 0.06, MFV - 81 ± 8 ml / min, respectively. These indices significantly (P <0.05) differed from the indices of the left VA in the case of left-sided localization of UVA. Conclusions. With antelisthesis, the deterioration of blood flow parameters in the form of a decrease in systolic peak velocity and minute blood volume, as well as an increase in resistance and pulsation indices, occurs during extension, and in retrolisthesis, on the contrary, with bending of the head. With uncovertebral arthrosis, the deterioration of hemodynamic parameters is better manifested with rotational head movements. A decrease in the systolic velocity and minute volume of blood flow, an increase in the indices of resistance and pulsation occur during impsilateral rotation of the head on the side of arthrosis. Key words: instability of the cervical vertebrae, uncovertebral arthrosis, duplex scanning, vertebral arteries, functional tests.
Article
Full-text available
The simulated manipulation position is one of several premanipulative screening tests recommended to assist in identifying patients at risk of complications from high velocity thrust manipulation of the cervical spine. The effects of this position on blood flow in the vertebral artery has been measured, but not in the internal carotid artery. Fourteen healthy subjects participated in a pre-test post-test single group study to determine the effect of a simulated manipulation position on blood flow in both the internal carotid and vertebral arteries. Duplex ultrasound with colour Doppler imaging was used to image the internal carotid and vertebral arteries and to measure blood flow velocity with the neck in neutral and simulated manipulation positions. A measure of distal vascular resistance, the resistance index, was calculated. There was a significant (p<0.05) reduction in the resistance index in the vertebral arteries ipsilateral to the rotation component of the simulated manipulation position. Placing the cervical spine in a simulated manipulation position, did not adversely affect blood flow through the internal carotid and vertebral arteries. Further research is needed to determine how the simulated manipulation position affects internal carotid and vertebral artery blood flow in individuals who have signs or symptoms of neurovascular insufficiency.
Article
The objective of the study was to investigate the cerebrovascular hemodynamic response of cervical spine positions including rotation and cervical spine manipulation in vivo using magnetic resonance imaging technology on the vertebral artery (VA). This pilot study was conducted as a blinded examiner cohort with 4 randomized clinical tasks. Ten healthy male participants aged 24 to 30 years (mean, 26.8 years) volunteered to participate in the study. None of the participants had a history of disabling neck, arm, or headache pain within the last 6 months. They did not have any current or history of neurologic symptoms. In a neutral head position, physiologic measures of VA blood flow and velocity at the C1-2 spinal level were obtained using phase-contrast magnetic resonance imaging after 3 different head positions and a chiropractic upper cervical spinal manipulation. A total of 30 flow-encoded phase-contrast images were collected over the cardiac cycle, in each of the 4 conditions, and were used to provide a blood flow profile for one complete cardiac cycle. Differences between flow (in milliliters per second) and velocity (in centimeters per second) variables were evaluated using repeated-measures analysis of variance. The side-to-side difference between ipsilateral and contralateral VA velocities was not significant for either velocities (P = .14) or flows (P = .19) throughout the conditions. There were no other interactions or trends toward a difference for any of the other blood flow or velocity variables. There were no significant changes in blood flow or velocity in the vertebral arteries of healthy young male adults after various head positions and cervical spine manipulations.
Article
Randomized clinical trial. To document the types and frequencies of adverse reactions associated with the most common chiropractic treatments for neck pain, and to identify possible clinical predictors of adverse reactions to chiropractic treatment. Chiropractic care is frequently sought by patients for relief from neck pain; however, adverse reactions related to its primary modes of treatment have not been well examined. A total of 336 patients with neck pain presenting to 4 southern California health care clinics were randomized in a balanced 2 x 2 x 2 factorial design to manipulation with or without heat, and with or without electrical muscle stimulation (EMS); and mobilization with or without heat and with or without EMS. Discomfort or unpleasant reactions from chiropractic care were self-assessed at 2 weeks after the randomization/baseline visit. Of the 280 participants (83%) who responded, 85 (30.4%) had 212 adverse symptoms as a result of chiropractic care. Increased neck pain or stiffness was the most common symptom, reported by 25% of the participants. Less common were headache and radiating pain. Patients randomized to manipulation were more likely than those randomized to mobilization to have an adverse symptom occurring within 24 hours of treatment (adjusted odds ratio [OR] = 1.44, 95% confidence interval [CI] = 0.83, 2.49). Heat and EMS were only weakly associated with adverse symptoms (heat: OR = 0.94, 95% CI = 0.54, 1.62; EMS: OR = 1.09, 95% CI = 0.63, 1.89). Moderate-to-severe neck disability at baseline was strongly associated with adverse neurologic symptoms (OR = 5.70, 95% CI = 1.49, 21.80). Our results suggest that adverse reactions to chiropractic care for neck pain are common and that despite somewhat imprecise estimation, adverse reactions appear more likely to follow cervical spine manipulation than mobilization. Given the possible higher risk of adverse reactions and lack of demonstrated effectiveness of manipulation over mobilization, chiropractors should consider a conservative approach for applying manipulation to their patients, especially those with severe neck pain.
Article
Benedict Wand and colleagues argue that the risks of cervical spine manipulation are not justified, but David Cassidy and colleagues (doi:10.1136/bmj.e3680) think it is a valuable addition to patient care.
Article
Benedict Wand and colleagues argue that the risks of cervical spine manipulation are not justified, but David Cassidy and colleagues (doi:10.1136/bmj.e3680) think it is a valuable addition to patient care Cervical spine manipulation (a high velocity, low amplitude, end range thrust manoeuvre) is a common treatment option for mechanical neck pain yet may carry the potential for serious neurovascular complications, specifically vertebral artery dissection and subsequent vertebrobasilar stroke. The non-superiority of manipulation to alternative treatments, coupled with concerns regarding safety, renders cervical spine manipulation unnecessary and inadvisable. The controversy surrounding the association between manipulation and neurovascular complications is longstanding and not fully resolved, partly because it is difficult to obtain conclusive evidence on rare adverse events. What can be accepted is that the incidence of vertebral artery dissection is low, with estimates between 1 (95% confidence interval 0.5 to 1.4) and 1.7 (1.1 to 2.3) per 100 000 person years in the United States.1 The estimates for stroke resulting from vertebral artery dissection are lower still, ranging from 0.75 to 1.12 per 100 000 person years,2 and many are unlikely to be the result of cervical …
Article
Many studies of vertebral artery (VA) blood flow changes related to cervical spine rotation have been published, but the findings are controversial and the evidence unconvincing. Recent Doppler measurements suggest that contralateral VA blood flow is compromised on full rotation in both healthy subjects and patients. More rigorous research is needed, and it was the aim of this study to conduct a meta-analysis of published data to inform professional practice. A systematic literature search, including only Doppler studies of VA blood flow velocity associated with cervical spine rotation in adults, yielded nine reports with published data. Using weighted means of the pooled data, the magnitude of the effect size (Cohen's d) was calculated for differences between patients and subjects, sitting or lying supine for testing, the parts of the VA insonated, and the changes recorded after cervical spine rotation. From this meta-analysis, VA blood flow velocity was found to be compromised more in patients than healthy individuals, on contralateral rotation, with the subject sitting, and more in the intracranial compared to the cervical part of the VA. Possible reasons for these findings are suggested, and it is advised that sustained end-of-range rotation and quick-thrust rotational manipulations be avoided until there is a stronger evidence base for clinical practice.
Article
Clinical tests involving sustained cervical spine rotation and/or extension are commonly applied pre-manipulatively to screen for patients at risk of stroke due to vertebral artery pathology. This is despite the fact that the validity of these manoeuvres is disputed and their effect on vertebral artery blood flow poorly understood. Recent research has mployed duplex ultrasound (Doppler with Bmode real-time imaging capability) to quantify positional haemodynamic parameters and determine whether subjects testing positive differ from negative subjects. However, the reliability of Doppler sampling of the upper cervical part of the vertebral artery in positions involving rotation and extension has not been established. Thus the aim of this study was to evaluate the reliability and measurement variability associated with this investigative procedure. Methods: Twenty normal subjects volunteered to participate in the study. Haemodynamic measurements were taken of a randomly selected vertebral artery using duplex ultrasound with colour flow and power Doppler imaging capabilities. Blood flow was recorded at both the atlanto-axial and the C2/3 regions of the vessel in neutral, end-range extension and end-range contralateral rotation. The protocol was then repeated. Results: Intraclass correlation coefficients (2, 1) and 95% limits of agreement indicated that sampling at the more vulnerable but less accessible atlanto-axial site was generally more repeatable, notably in end-range contralateral rotation. In particular, the key measures of atlanto-axial peak systolic velocity and resistance index in end-range rotation demonstrated excellent reliability (0.82; 0.76). Between group differences of –12.9 to 16.6 cm/s and –0.11 to 0.17 respectively would be necessary to discount measurement variability. Conclusions: Accurate interpretation of the results of ultrasonographic investigation of vertebral artery tests utilising rotation and extension requires consideration of measurement variability and reliability. Haemodynamic parameters of acceptable reliability and associated ranges of measurement variability have been identified for use in future research. Yes Yes
Article
The purpose of this study was to determine the use of manipulation and mobilisation by the Chartered Physiotherapists (CMPT) in Manipulative Therapy Ireland and to describe adverse effects associated with the use of these techniques. A 44 item postal survey was sent to all 259 members of the CPMT (response rate 49%, n=127). All 127 respondents used non-High Velocity Thrust Techniques (HVTT) and 27% (n=34) used HVTT. Nine percent (n=12) used HVTT on the upper cervical spine. Twenty six percent (n=33) reported an adverse effect in the previous 2 years. The adverse effects were associated with the use of HVTT (4%, n=5), non-HVTT (20%, n=26) and cervical traction (2%, n=2). The most serious adverse effects were associated with non-HVTT and included 1 drop attack, 1 fainting episode and 1 Transient Ischemic Attack (TIA) 4 days post treatment. Fifty three percent (n=18) of HVTT users and 40% (n=44) of non-HVTT users reported carrying out a vertebrobasilar insufficiency (VBI) assessment. The study shows that VBI assessment may not detect every patient at risk of adverse effects. Large scale studies to investigate the risk of serious adverse reactions are needed. A system of reporting adverse effects on a routine basis could be considered.