Upload
raghavendra-prasad
View
232
Download
0
Embed Size (px)
Citation preview
8/12/2019 Cervical Spine Block
1/15
Cervical Spine Ultrasonography
Dr. Geoff A Bellingham MD FRCPC
Department of Anesthesia & Perioperative Medicine
Schulich School of Medicine & Dentistry, Western University
London, Ontario, Canada
Table of Contents
1. Type of Probe Used
2. Counting Levels
3. Cervical Facet Joint Injections
4. Cervical Medial Branch Blocks
5. Cervical Nerve Root Blocks
6. Vascular Anatomy of the Cervical Spine
1. Type of Probe Used
Cervical spinal structures are typically superficial to skin but can vary in depth depending on the
body habitus of the patient. As such, ultrasound probes with higher frequencies (14-5 MHz) can
usually be used to provide clinicians with good spatial resolution. Increased spatial resolutionwill mean better definition of the tissue structures but does sacrifice the depth of penetration of
the beam.
2. Counting Levels
The ability to identify vertebral levels of the cervical spine using ultrasound relies on visualizing
characteristic anatomical boney landmarks and vessels unique to each vertebrae. There are three
reported methods for counting levels.
The first method which has been described relies on a midline sagittal scan of the cervical spine
to count the levels starting cranial to caudad. This technique relies on identifying characteristic
shapes of the spinous processes. The spinous processes of C2 to C6 have varying frequencies of
bifidity/nonbifidity. In contrast, the atlas (C1) has no true spine and consists of two lateral
masses connected posteriorly by a long, curved arch. One may rely on the relative absence of a
spinous process in a sagittal plane to identify C1 and to then count caudally to the desired level
(Figures 1 A and B).
8/12/2019 Cervical Spine Block
2/15
Figure 1.A. Midline longitudinal scan over the cervical spinous processes. C1 has only a rudimentary spinousprocess. B. Short axis view demonstrating bifid spinous process of C2 (arrows).
Narouze SM. Ultrasound guided cervical spine injections: Ultrasound prevents whereas contrast fluoroscopyDetects intravascular injections. Regional Anesthesia and Pain Medicine 37 (2): 127-30.
It has been suggested to use the bifid morphology of the C2 spinous process to act as an
additional boney landmark to help verify the vertebral level. This is best appreciated using a
transverse scan. However, the spinous processes from C2-C6 have varying degrees of bifidity
and consistency in this feature is lacking. In a recent anatomical study performed in South
Africa, only 58.9% of caucasian spines had the presence of bifid spinous processes and only
31.6% were found in the black specimens studied. When this did occur, C2 was the most
common level to have this feature (89%), followed by C5 (83%), C4 (79%), C3 (59.4%), and C6
(41.7%) (Asvat R 2012). Given the variation in morphology, bifidity should not be a sonographic
landmark used to assist in identifying vertebral levels. This has been also corroborated in surgical
literature (Moro T et al. 2007).
The most significant and consistent anatomical feature that can be appreciated on scanning the
cervical spine are the characteristic morphologies of the transverse processes. Only C3-C6 have
an anterior and posterior tubercle with a groove for the spinal nerve between them. Under
ultrasound, these tubercles are hyperechoic and provide a characteristic 2-humped camel sign
(Narouze et al. 2009). The C6 level distinguishes itself by having the most prominent anterior
tubercle compared to other levels, referred to classically as Chassaignacs tubercle. The C7
vertebra distinguishes itself by having only a rudimentary anterior tubercle and a prominent
posterior tubercle (Martinoli C et al. 2002).
The level of the C6 vertebra can be roughly identified through use of the cricoid cartilage as a
surface landmark. Placing the ultrasound probe laterally and in a transverse plane on the neck,
one may appreciate the double hump of the anterior and posterior tubercle of its transverse
process (Figure 2). This level can be confirmed by moving the probe caudally to the C7 level. If
8/12/2019 Cervical Spine Block
3/15
correct, one should only appreciate the single posterior tubercle of C7 with the nerve root and
vertebral artery lying anteriorly (Figure 3).
Figure 2.Axial transverse ultrasound image showing the prominent anterior tubercle (at) of the C6 transverseprocess (C6 TP). N represents nerve root; CA, carotid artery; pt, posterior tubercle.
Figure 3.Axial transverse ultrasound image showing the characteristic morphology of the C7 transverse process(TP). C7 represents nerve root; VA, vertebral artery. The vertebral artery lies anterior to the C7 nerve root.
Narouze SN, Vydyanathan A, Kapural L, Sessler DI, and Mekhail N. Ultrasound-guided cervical selective nerve rootblock. Reg Anesth Pain Med 2009; 34: 343-348.
8/12/2019 Cervical Spine Block
4/15
The final method utilizes the relative position of the vertebral artery to the transverse processes,
as reported by Narouze et al. (2009). At the C7 level, the artery runs anterior to the transverse
process prior to entering the foramen of the C6 transverse process in 90% of cases. (Narouze SN
2011a)
3. Cervical Facet Joint Injections
There have been two proposed techniques to perform ultrasound guided cervical facet joint
injections.
An antero-lateral approach has been reported by Galiano et al. (2006). The report assessed the
feasibility of identifying the zygapophyseal joints under ultrasound followed by ultrasound
guided needle placement accuracy. Needles were guided to the zygapophyseal joints from C2-3
to C6-7 on both sides of one cadaver, and intra-articular placement was confirmed via computed
tomography.
Of 40 ultrasound examinations between C2-3 to C6-7, the joint space was not depicted on 4
attempts. All 10 needle tips were located in the joint space during the simulated injections, which
were verified by CT.
All cadavers were positioned in a lateral position. The technique used to identify the proper level
relied on identification of the transverse processes of the sixth and seventh vertebrae. Once the
appropriate level was identified, the transducer was positioned in an axial plane, with the joint
space in the middle of the image. This view allowed for the guidance of a needle from an antero-
lateral approach. The facet joints appeared as hyperechoic signals, with the joint space appearing
as an anechoic gap between the articular processes (Figure 4).
8/12/2019 Cervical Spine Block
5/15
A posterior approach to cervical facet intra-articular injection has been proposed by Narouze
(Narouze S.N. 2011b). A proposed advantage is that the patient does not have to change positions
if the injections are to be performed bilaterally.
A sagittal scan is first obtained at midline to identify the correct cervical level. By moving the
probe laterally, the next sonographic image produced is that of the lamina of the cervical
vertebrae. Moving further laterally, the facet column will next appear with a characteristic saw
sign. (Figure 5) If doubt exists if the saw sign represents the lamina or facet pillar, scanning
further laterally should only reveal soft tissue representative of the paraspinal muscles, and no
bone. This can help to confirm that the boney saw sign image produced was representative of
the facets, the most lateral structures in the posterior spine.
Injections of the facet joints can then be performed by advancing the needle from the caudal
aspect of the ultrasound probe.
Figure 4.A, Axial transverse ultrasound image of a cervical facet jointinfiltration at level C6-7 demonstrating the needle placement in thetarget area, using a linear transducer (L12-5 MHz). B, Correspondingaxial transverse CT image of a cervical facet joint infiltration at levelC6-7. The box outlines the location of the ultrasound image. C,Schematic drawing of the facet joint injection. The needles are inserted
at an angle (a) of 60 to 75 degrees in respect to the parasagittal plane.iap, inferior articular process; js, joint space; l, lamina; n, needle; ntneedle tip; sap, superior articular process; sp, spinous process; vb,vertebral body.
Galiano K, Obwegeser AA, Bodner G, Freund MC, Gruber H, MaurerH, Schatzer R, Fiegele T, and Ploner F. Ultrasound-guided facet jointinjections in the middle to lower cervical spine. Clin J Pain 2006; 22:538-543.
Figure 5.Sagittal longitudinalsonogram showing the articular
processes of the facet joints asthe saw sign. The white arrow
points to the C45 facet jointspace and indicates the path aneedle could be guided to
perform an intraarticularinjection.
8/12/2019 Cervical Spine Block
6/15
4. Cervical Medial Branch Blocks
There have been two studies which have assessed the feasibility of third occipital nerve and
cervical medial branch blocks under ultrasound guidance.
The first investigation to report neural blockade of cervical zygapophysial joints focused on
targeting the third occipital nerve. In this study, authors described the technique used and
confirmed that the nerve could be visualized bilaterally in all 14 volunteers studied. Needles
were then directed under ultrasound guidance to the nerve and were correctly placed 23 out of 28
attempts, confirmed via fluoroscopy (Eichenberger U et al. 2006).
Investigators performed the injection by placing the ultrasound probe perpendicular to the lateral
aspect of the neck nearly in a transverse plane, starting just caudal to the mastoid process.
Volunteers were placed in a lateral position. As the probe was moved caudally, the transverse
process of C1 could be visualized. Moving further caudal by approximately 2 cm, the transverseprocess of C2 could next be identified. (Refer to Figure 6A)
Once this image was obtained, the transducer was moved 5-8 mm posteriorly to visualize the
arch of the atlas (C1) and the articular pillar of C2 (cranial part of the C2-3 facet joint). With this
view, the probe could be slid caudally to obtain a view of the facet joints of C2-3 and C3-4. The
third occipital nerve crossed the articulation of C2-3 and could be searched for over the
articulation, approximately 1 mm from the bone, with a median diameter of 2.0 mm. (Figures 6
A-C)
Performance of the injection was described as an out of plane approach by the authors. The
needle was introduced immediately anterior to the ultrasound probe and advanced perpendicular
to the beam until it reaches the desired target point.
8/12/2019 Cervical Spine Block
7/15
Figure 6B.Ultrasound image transverse view of the C2C3 zygapophysial joint. The gray circle indicates the targetpoint for the needle tip during the ultrasound-guided needle placement for third occipital nerve block. 1 C2C3 jointline; 2 superior articular process of C3; 3 inferior articular process of C2; 4 intervertebral foramen of C2C3; C3white reflex of the surface of the vertebral body of C3; LS levator scapulae muscle; SCM sternocleidomastoidmuscle; SM scalenus medius muscle; TM trapezius muscle; TR ultrasound shadow of the transverse process of C2.
Eichenberger U, Greher M, Kapral S, Marhofer P, Wiest R, Remonda L, Bogduk N, and Guratolo M. Sonographicvisualization and ultrasound-guided block of the third occipital nerve. Anesthesiology 2006; 104: 303-8.
Figure 6A.Cervical spine (C2C5): Transducer alignment in relation tothe cervical spine for ultrasound-guided third occipital nerve block (asreported by Eichenberger U et al. 2006) in the transverse view (TV) andthe longitudinal view (LV). The circle indicates the target point.
Eichenberger U, Greher M, Kapral S, Marhofer P, Wiest R, Remonda L,Bogduk N, and Guratolo M. Sonographic visualization and ultrasound-guided block of the third occipital nerve. Anesthesiology 2006; 104:303-8.
8/12/2019 Cervical Spine Block
8/15
Figure 6C.Ultrasound image longitudinal view (LV) along the articular pillars from C2 to C5. LC longissimuscapitis muscle; LS levator scapulae muscle; SC splenius capitis muscle; SCM sternocleidomastoid muscle; SMCsemispinalis capitis muscle.
Eichenberger U, Greher M, Kapral S, Marhofer P, Wiest R, Remonda L, Bogduk N, and Guratolo M. Sonographicvisualization and ultrasound-guided block of the third occipital nerve. Anesthesiology 2006; 104: 303-8.
The second investigation sought to block the medial branches between C3 and C6 under
ultrasound guidance. Of 46 cervical medial branch blocks, all needle tips were positioned on the
articular pillars. The second phase of the study used contrast to evaluate the spread of 0.3 mL of
contrast/local anesthetic. Contrast was found to cover the appropriate level in 94.5% of cases
without complications. The incidence of aberrant spread to adjacent levels was 13.5%, similar to
reports using fluoroscopy. (Finlayson RJ et al. 2012)
Investigators identified the appropriate level for C3 and C4 medial branch blocks by firstscanning in the coronal plane and identifying a drop-off representing the C2-C3 junction.
Scanning caudally from this junction, the articular pillar of C3 and subsequently C4 could be
identified. Identification of the C6 and C7 levels was performed by identifying the characteristic
structures of the transverse processes (as described in Section 2).
For all levels scanned and injected, the probe was oriented in the transverse plane. The scan
started posteriorly to identify the spinous process and lamina. The probe then moved anteriorly to
identify the contour of the articular process. Once satisfied that an echogenic linear image of the
bone of the pillar was achieved, the probe was tilted slighted posteriorly to maximize the length
of the image, following the long axis of the pillar. (Figure 7) Color Doppler was performed to
identify any blood vessels near the proximity of the target. The needle was then inserted in plane
from a postero-lateral approach.
8/12/2019 Cervical Spine Block
9/15
Figure 7.A, Transverse scan at the level of C4 showing needle in position after injection. B, Explanatory linedrawing needle (N), local anesthetic (LA), lamina (Lam), articular pillar (AP), posterior tubercle (PT) of TP.
Finlayson RJ, Gupta G, Alhujairi M, Dugani S, Tran DQH. Cervical medial branch block: A novel technique using
ultrasound guidance. Reg Anesth Pain Med 2012; 37: 219-223.
5. Cervical Nerve Root Blocks
The feasibility of selected cervical nerve root blocks has been evaluated in three studies
(Narouze et al. 2009, Yamauchi et al. 2011, and Galiano et al. 2005), two of which involved
injecting patients with fluoroscopic confirmation of correct needle position. All studies reported
that identification of the correct cervical level can be obtained. Guidance of a needle to the nerve
root can also be accomplished safely, with the added benefit of detection of critical vessels
supplying the nerve roots and spinal cord. However, the studies suggested that spread of solution
remains limited to the extraforaminal portions of the nerve root targeted.
The technique employed by Narouze et al. (2009) seems to provide the most ergonomic approach
for performing this injection. Patients are placed in a lateral decubitus position so that an
ultrasound probe can be applied to the lateral aspect of the neck. This allows the examiner the
ability to identify the transverse processes easily in order to determine cervical level (as
described in Section 2). A linear high-frequency array is used.
Once an optimum transverse view of the transverse processes is obtained, slight tilting of the
transducer is used to visualize the spinal nerve as a round hypoechoic signal. Between levels C3-
C6, the nerve can be found situated between the anterior and posterior tubercles of the transverseprocesses. (Figure 8) At C7, the spinal nerve is seen to lie anterior to the prominent posterior
tubercle only. Again, the rudimentary anterior tubercle is not seen in this view, and the vertebral
artery is observed to be lying anterior the nerve itself.
After the proper sonoanatomy is delineated, color doppler can be used to help identify any
critical vessels in the vicinity of the nerve route in addition to the proposed path of the needle to
be used to block the nerve.
8/12/2019 Cervical Spine Block
10/15
A 22-guage, blunt-tip needle can be introduced lateral to the lateral end of the transducer. The
needle is advanced in the plane of the ultrasound beam from posterior to anterior to the desired
nerve root at the foraminal opening.
As described by Narouze et al (2009), diagnostic blocks were performed by injecting 2 mL of1% lidocaine. Therapeutic blocks used a mixture of dexamethasone (8 mg) and 1% lidocaine.
Figure 8.A, Axial transverse ultrasound image showing the sharp anterior tubercle (at) of the C6 transverse process
(C6 TP). N indicates nerve root; CA, carotid artery; pt, posterior tubercle. Solid arrows point to the needle in placeat the posterior aspect of the intervertebral foramen. B, Illustration showing the relevant anatomy at C6 level and theorientation of the ultrasound transducer.
Narouze SN, Vydyanathan A, Kapural L, Sessler DI, and Mekhail N. Ultrasound-guided cervical selective nerve rootblock. Reg Anesth Pain Med 2009; 34: 343-348.
6. Vascular Anatomy of the Cervical Spine
One of the advantages of using ultrasound for cervical spine interventions is the ability to
visualize vascular structures. In contrast to fluoroscopic guided interventions, physicians can
identify and avoid injury to vessels rather than identifying vascular cannulation after it has
occurred through the injection of contrast dye.
Published reports of catastrophic injuries from vascular insult in this region include paralysis,
brain injury, and even death (Baker R et al 2003, Brouwers PJ et al 2001, Rozin L et al 2003,
Tiso RL et al 2004). An understanding of the vascular anatomy of the cervical spine is therefore
an important component of ultrasound based techniques for cervical spine interventions.
8/12/2019 Cervical Spine Block
11/15
The blood supply to the spinal cord is derived from a single anterior artery and paired posterior
spinal arteries which run in a cephalad to caudad direction (Hoeft MA et al. 2006). The supply is
segmental in nature and relies on the blood supplied by radicular arteries which enter via the
intervertebral foramina. Consequently, any injury or compression of the radicular arteries (and
their blood supply) can lead to ischemic damage to the spinal cord.
The radicular arteries most often run anterior to the spinal nerve, and are least likely to be found
posterior to it (Turnbull IM et al. 1966, Huntoon M. 2005). Arteries tend to enter the foramina
inferior to the spinal nerve and follow a tortuous course along the inferior and anterior aspect of
the nerve. The approximate location of the radicular arteries within the foramina tends to be
determined by the vessels from which they originate. Those which originate from the vertebral
artery lie over the most anteromedial aspect of the foramen (Hoeft M et al. 2006). Figure 9
Figure 9.Axial view of cervical transforaminal injection at the level of C6. Arterial branches arise variably from thevertebral artery to supply the nerve root itself or to join the anterior or posterior spinal artery. Spinal segmentalarteries that arise from the depth of the ascending cervical artery enter the foramen at variable locations and oftencourse through the foramen, penetrate the dura, and join the anterior or posterior spinal arteries that supply the spinalcord. The needle placement is representative of a fluoroscopically guided transforaminal injection.
Hoeft MA, Rathmell JP, Monsey RD, and Fonda BJ. Cervical transforaminal injection and the radicular artery:Variation in anatomical location within the cervical intervertebral foramina. Regional Anesthesia and Pain Medicine31 (3) 2006: 270-274.
The variations in blood supply to the radicular arteries has been investigated in several
anatomical studies. The anastamoses of these vessels are numerous and varied but are typically
reported to come from the vertebral, ascending cervical, superior intercostals, and deep cervical
8/12/2019 Cervical Spine Block
12/15
arteries. The dominant blood supply for the radicular arteries originate from the vertebral
arteries. In an anatomical study of 35 fetal and adult cadavers, 80% of radicular arteries in the
cervical region originated from these vertebral vessels (Dommisse et al. 1974). In the same
study, the remainder of radicular anastamoses originated from the deep cervical and superior
intercostal arteries, and occasionally from the ascending cervical artery.
Those radicular arteries that arise from the deep cervical, superior intercostals or ascending
cervical arteries can traverse the entire extent of the foramen. (Figure 10) It is this group of
vessels that may be at particular risk of injury from interventions given the variation in anatomy.
In an anatomical study of 95 intervertebral cervical foramina, 21 had an arterial vessel proximal
to the posterior aspect of the foraminal opening. Seven of these were spinal branches that entered
the foramen posteriorly, potentially forming radicular or segmental medullary vessels to the
spinal cord (Huntoon M 2005).
In the study by Huntoon M (2005), the ascending cervical artery typically ascended on the
anterior tubercles of the transverse processes, with an average outer diameter of 1.0 mm. If itcame to supply a spinal branch, it typically occurred at the C3-4 or C4-5 foramen, entering the
posterior and inferior aspect of the foraminal opening (Huntoon M 2005).
The deep cervical arteries commonly provided branches to the roots of the brachial plexus.
However, in five instances, the vessels formed large spinal branches and entered the posterior
aspect of the foramen, directly posterior to the exiting ventral ramus. These critical vessels were
observed to always enter at either C5-6, C6-7, or C7-T1 (Huntoon M 2005).
Thus far in studies concerning ultrasound based interventions of the cervical spine, posterior and
lateral approaches with a needle are most commonly used. This assists in avoiding injury to thevertebral artery. However, radicular arteries which enter the foramina originating from the deep
cervical, ascending cervical and superior intercostals are those which if injured, could cause
deleterious consequences. These are the additional vessels which should be sought using doppler
techniques prior to needle insertion.
8/12/2019 Cervical Spine Block
13/15
Figure 10.Illustrations demonstrating ascending cervical and deep cervical arteries anastomosing with the vertebralartery posterior to the spinal nerves. The needle placement is representative of a fluoroscopically guidedtransforaminal injection. The intention of the authors paper is to illustrate the potential for vessel injury using thefluoroscopically guided technique.
Huntoon MA. Anatomy of the cervical intervertebral foramina: vulnerable arteries and ischemic neurologic injuriesafter transforaminal epidural injections. Pain 117 (2005): 104-11.
References
Asvat R. The configuration of cervical spinous processes in black and white South African
skeletal samples.J Forensic Sci2012; 57 (1): 176-181.
Baker R, Dreyfuss P, Mercer S, Bogduk N. Cervical transforaminal injection of corticosteroids
into a radicular artery: a possible mechanism for spinal cord injury.Pain2003;103: 2115.
Brouwers PJ, Kottink EJ, Simon MA, Prevo RL. A cervical anterior spinal artery syndrome after
diagnostic blockade of the right C6-nerve root.Pain2001; 91: 3979.
Dommisse GF. The blood supply of the spinal cord: A critical vascular zone in spinal surgery.J
Bone Joint Surg Br 1974; 56: 225-235.
Eichenberger U, Greher M, Kapral S, et al. Sonographic visualization and ultrasound-guided
block of the third occipital nerve - prospective for a new method to diagnose C2YC3
zygapophysial joint pain.Anesthesiology2006; 104: 303-308.
8/12/2019 Cervical Spine Block
14/15
Finlayson RJ, Gupta G, Alhujairi M, Dugani S, Tran DQH. Cervical medial branch block: A
novel technique using ultrasound guidance.Reg Anesth Pain Med2012; 37: 219-223.
Galiano K, Obwegeser AA, Bodner G, Freund MC, Gruber H, Maurer H, Schatzer R, Fiegele T,
and Ploner F. Ultrasound-guided facet joint injections in the middle to lower cervical spine. Clin
J Pain2006; 22: 538-543.
Galiano K, Obwegeser AA, Bodner G, Freund MC, Gruber H, Maurer H, Schatzer R, and Ploner
F. Ultrasound-guided periradicular injections in the middle to lower cervical spine: An imaging
study of a new approach.Reg Anesth Pain Med2005; 30 (4): 391-396.
Hoeft MA, Rathmell JP, Monsey RD, ad Fonda BJ. Cervical transforaminal injection and the
radicular artery: Variation in anatomical location within the cervical intervertebral foramina.Reg
Anesth Pain Med2006 31 (3): 270-274.
Huntoon M. Anatomy of the cervical intervertebral foramina: Vulnerable arteries and ischemicneurologic injuries after transforaminal epidural injections.Pain2005; 117: 10411.
Martinoli C, Bianchi S, Santacroce E, Pugliese F, Graif M, Derchi LE. Brachial plexus
sonography: a technique for assessing the root level.AJR Am J Roentgenol2002; 179: 699-702.
Moro T, Kikuchi S, Konno S, Nishiyama K. Cervical spinous process bifurcation is not useful as
a landmark in posterior cervical spine approach.Fukushima J Med Sci2007 53 (1): 19-25.
Narouze SN, Vydyanathan A, Kapural L, Sessler DI, and Mekhail N. Ultrasound-guided cervical
selective nerve root block.Reg Anesth Pain Med2009; 34: 343-348.
Narouze S.N. (2011a) Ultrasound-Guided Cervical Nerve Root Block. In S.N. Narouze (Ed.),
Atlas of Ultrasound Guided Procedures in Interventional Pain Management (125-131).New
York; Springer.
Narouze S.N. (2011b) Ultrasound-Guided Cervical Zygapophyseal (Facet) Intra-Articular
Injection. In S.N. Narouze (Ed.),Atlas of Ultrasound Guided Procedures in Interventional Pain
Management (119-123).New York; Springer.
Rozin L, Rozin R, Koehler SA, Shakir A, Ladham S, Barmada M, Dominick J, Wecht CH. Death
during transforaminal epidural steroid nerve root block (C7) due to perforation of the left
vertebral artery.Am J Forensic Med Pathol2003; 24: 3515.
Tiso RL, Cutler T, Catania JA, Whalen K. Adverse central nervous system sequelae after
selective transforaminal block: the role of corticosteroids. Spine J2004; 4: 46874.
8/12/2019 Cervical Spine Block
15/15
Turnbull IM, Brieg A, Hassler O. Blood supply of cervical spinal cord in man: A
microangiographic cadaver study.J Neurosurg1966; 24: 95165.
Su WD, Ohtsuka A, Taguchi T, and Murakami T. Typology of the arteries in the human scalenus
region, with special reference to the accessory ascending cervical artery.Acta Med Okayama
2000; 54 (6): 243-252.
Yamauchi M, Suzuki D, Niya T, Honma H, Tachibana N, Watanabe A, Fujimiya M, and
Yamakage M. Ultrasound-guided cervical nerve root block: Spread of solution and clinical
effect.Pain Medicine2011; 12: 1190-1195.