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Review
Ultrasound-guided cervical selective nerve root injections: a narrative review of literature
  1. Reza Ehsanian1,
  2. Byron J Schneider2,
  3. David J Kennedy2 and
  4. Eugene Koshkin3
  1. 1 Division of Physical Medicine and Rehabilitation, Department of Orthopaedics & Rehabilitation, University of New Mexico School of Medicine, Albuquerque, New Mexico, USA
  2. 2 Department of Physical Medicine and Rehabilitation, Vanderbilt University Medical Center, Nashville, Tennessee, USA
  3. 3 Department of Anesthesia & Critical Care Medicine, University of New Mexico School of Medicine, Albuquerque, New Mexico, USA
  1. Correspondence to Dr Eugene Koshkin, Department of Anesthesia & Critical Care Medicine, University of New Mexico School of Medicine, Albuquerque, New Mexico, USA; hsc-painmedicine{at}salud.unm.edu

Abstract

Background/Importance Ultrasound (US)-guided cervical selective nerve root injections (CSNRI) have been proposed as an alternative to fluoroscopic (FL) -guided injections. When choosing US guidance, the proceduralist should be aware of potential issues confirming vertebral level, be clear regarding terminology, and up to date regarding the advantages and disadvantages of US-guided CSNRI.

Objective Review the accuracy and effectiveness of US guidance in avoiding vascular puncture (VP) and/or intravascular injection (IVI) during CSNRI.

Evidence Review Queries included PubMed, CINAHL and Embase databases from 2005 to 2019. Three authors reviewed references for eligibility, abstracted data, and appraised quality.

Findings The literature demonstrates distinct safety considerations and limited evidence of the effectiveness of US guidance in detecting VP and/or IVI. As vascular flow and desired injectate spread cannot be visualized with US, the use of real-time fluoroscopy, and if needed digitial subraction imaging, is indicated in cervical transforaminal epidural injections (CTFEIs). Given the risk of VP and/or IVI, the ability to perform and to retain FL images to document that the procedure was safely conducted is valuable in CTFEIs.

Conclusion US guidance remains to be proven as a non-inferior alternative to FL guidance or other imaging modalities in the prevention of VP and/or IVI with CTFEIs or cervical selective nerve root blocks. There is a paucity of adequately powered clinical studies evaluating the accuracy and effectiveness of US guidance in avoiding VP and/or IVI. US-guided procedures to treat cervical radicular pain has limitations in visualization of anatomy, and currently with the evidence available is best used in a combined approach with FL guidance.

  • injections
  • spinal
  • back pain
  • neck pain
  • pain management
  • ultrasonography

Data availability statement

Data analyzed in this study were a re-analysis of existing data, which are openly available at locations cited in the reference section. Further documentation about data processing is not applicable.

https://doi.org/10.1136/rapm-2020-102325

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    Introduction

    The current review will discuss results from the peer-reviewed literature on the accuracy and effectiveness of ultrasound (US) guidance in detecting vascular puncture (VP) and/or intravascular injection (IVI). The objective is to provide a synthesized review of the available literature. It is intended to inform practitioners contemplating the use of US guidance by addressing the accuracy and effectiveness of cervical US utilization in detection of VP and/or IVI during selective cervical nerve root injection for the treatment and diagnosis of cervical radicular pain. The ultimate goal of the review is to fuel further research to establish evidence for the use of US-guided cervical interventions, better guide treatment decisions for patients, and provoke scholarly dialog.

    Methods

    Sources of information

    Queries included PubMed, CINAHL and Embase electronic databases from January 2005 to April 2019 in order to assure that the current manuscript provides a comprehensive review of the topic. Additional sources included reference lists from reviewed articles, authoritative texts, personal contacts with experts, and non-indexed peer-reviewed literature. The results of the search were combined with a discussion to facilitate a narrative review.

    Search terms

    The initial search terms used included ‘ultrasound’ and ‘cervical’ and ‘injection’ to develop a draft abstract and outline of the manuscript. The final search terms for delimiting the review of the electronic databases listed above were determined using the draft abstract to search the Medical Subject Headings (MeSH) on demand site (https://meshb.nlm.nih.gov/MeSHonDemand) to identify MeSH terms. The MeSH Terms included ‘Spine’, ‘Fluoroscopy’, ‘Injections’, ‘Neck’ and ‘Ultrasonography’ and these terms as well as those included in online supplemental file 1 were used to conduct the final interrogation of the electronic databases in order to set reasonable boundaries to ensure a search comprehensive enough to attain all pertinent studies but focused enough to attain relevant literature. The final search was conducted in collaboration with the Health Sciences Informationist at the Eskind Biomedical Library at Vanderbilt University. The details of the search strategy are available in online supplemental file 1.

    Supplemental material

    Selection criteria

    Inclusion criteria included human studies, written in English, that described the use of US guidance to address cervical radicular pain. The exclusion criteria included animal studies, studies not available in English, as well as studies investigating, superficial cervical plexus block, stellate ganglion block, greater occipital nerve block, third occipital nerve blocks, cervical medial branch blocks, and facet joint injections. Publications that described peripheral nerve blocks and interlaminar and trigger point injections using US guidance were also excluded from this review. Inclusion and/or exclusion of manuscripts were determined by both RE and BJS.

    Statistics

    When possible and in order to give context to proportions and percentages presented, the authors calculated the 95% confidence interval (CI) of the proportions or counts presented. The number of subjects or injections of one of the categorical outcomes was used as the numerator and the total number of subjects or injections was used as the denominator. The CIs were calculated using the modified Wald method.1

    Background

    Cervical radiculitis

    A brief review of the levels of nerve compression is essential in order to contextualize the need for accuracy when delivering the drug of choice during the cervical injection for the treatment of cervical radiculitis (figure 1). Cervical radiculitis develops secondary to nerve root irritation at the level of the disc, the level of the lateral recess, within the foramen, and lateral to the foramen; although it should be noted that nerve compression may appear on imaging in asymptomatic patients (figure 1).2–11 At the level of the disc the common etiology of compression is disc herniation2 4 and spinal stenosis.12 13 A detailed review of disc nomenclature and herniation classification are beyond the scope of this review and the reader is directed to the publication from the combined task forces of the North American Spine Society, the American Society of Spine Radiology, and the American Society of Neuroradiology.14 Unlike the lumbar spine where the traversing nerve root is commonly affected, in the cervical spine disc herniations and spondylosis most often affect the exiting nerve root. Herniations of the C6-7 disc with C7 compression (45%–60%) is most common followed by C5-6 disc with C6 compression (20%–25%), and less commonly C4-5 and C7-T1 disc herniation with C5 and C8 compression (10%).2–4 In adults, spondylosis is the most common cause of spinal stenosis; however, spinal stenosis has many etiologies12 13. At the level of the lateral recess compression occurs secondary to facet arthrosis usually in combination with ligamentum flavum hypertrophy15. Narrowing of the foramen also develops secondary to facet arthrosis, as well as spondylolisthesis and disc herniation. The extraforaminal segment is an uncommon area for compression. Narrowing at the extraforaminal segment is secondary to a lateral disc herniation (figure 1).

    Figure 1
    Figure 1

    Four levels of nerve compression. (A) Coronal computed tomography (CT) image with a graphic representation of the levels of nerve compression including at the level of the disc (Disc), at the level of the lateral recess (Lateral Recess), within the foramen (Foramen), and lateral to the foramen (Extra-foraminal). (B) Enlargement of the illustration in panel A. (CT image is a modified version of CT image, reproduced with permission, from http://headneckbrainspine.com and for which http://headneckbrainspine.com holds copyright).

    Cervical interlaminar and transforaminal epidural injection

    The proposed benefit of steroid injection is based on the premise that it decreases pain and local inflammation when delivered to the level/region of nerve compression (figure 1). The hypothesized mechanism of action is the local disruption of inflammatory cascades which increase phospholipase A2 activity and increase inflammation via matrix nitric oxide, metalloproteinases, prostaglandin E2 and interleukin 6; as well as by modulation of nociceptive C fibers16–22. The current peer-reviewed literature has established the safety, accuracy and efficacy of the delivery of corticosteroid into the epidural space via a fluoroscopically guided interlaminar23–30 or transforaminal24 30–40 approach in treating cervical radiculitis.3 21 41 42

    Results and Discussion

    Early anatomic studies investigating US-guided injection

    One of the first studies of the US-guided approach to the periradicular area was done in the lumbar spine as part of a cadaver study with authors in a subsequent paper describing the use of US guidance in performing cervical periradicular injections in cadavers.43 44 The major limitation of the study was the inability to comment on the vascular anatomy pertinent to the injection (figure 2).45 46 Subsequent studies demonstrated that the ventrodorsal oblique approach is prone to adverse events such as spinal cord injury as well as damage and/or injection to the cervical artery (ascending and deep) and/or spinal branches forming radicular or segmental feeder vessels to the spinal cord (figure 2).47–49 One study using US to evaluate the C4-5, C5-6 and C6-7 neuroforamina reported the presence of artery or vein in 4/74 (0.05; 95% CI: 0.0172 to 0.1350), 9/74 (0.12; 95% CI: 0.0631 to 0.2174) and 10/74 (0.14; 95% CI: 0.0731 to 0.2331) of these foramina, respectively.50 Notably, these incidences are significantly lower than those obtained using cadaveric dissection to identify vulnerable arteries in the cervical neuroforamina, reported to be present in 21/95 (0.22; 95% CI 0.1487 to 0.3151) of the intervertebral foramina dissected.48

    Figure 2
    Figure 2

    Stylized relationship of arterial vasculature relative to the cervical foreman. (Image is a modified version of the image from Stout in Physical Medicine and Rehabilitation Clinics of North America, Volume:22, Issue:1 21, reproduced with permission, and for which Mayo Foundation for Medical Education and Research holds copyright.)

    Confirming vertebral level US-guided injections

    Proper identification of cervical level is critical when positioning the needle for injections into the spinal column. There are multiple proposed techniques to properly identify the correct vertebral segment when performing an US-guided cervical injection.47 51 Some techniques, such as identifying where the vertebral artery enters a foramen, inherently lack sufficient specificity due to anatomic variability between patients.45 46 However, even in experienced hands there is an increased risk of miscount of the cervical spine, ‘something that can be easily avoided using fluoroscopy’.52 The issue of miscount has not been specifically studied however in one report 2/50 (0.04; 95% CI: 0.0034 to 0.1422) patients undergoing US-guided injection were injected at the wrong level.53 While other US techniques may be more reliable than the one used in the study cited, and may help to prevent incorrect vertebral level placement,52 they all lack a means of acquiring an image confirming that the appropriate vertebral segment was targeted. Standard fluoroscopic (FL) projections, on the other hand, quickly and reliably identify all relevant landmarks.54

    Terminology used for US-guided selective nerve root block

    It should be emphasized that the terms selective nerve root block, nerve root block, or selective nerve root injection are not interchangeable in practice or in the literature with transforaminal epidural injection. Narouze et al appropriately referred to cervical injections as ‘cervical selective nerve root block’ rather than cervical transforaminal epidural injection (CTFEI) because with US guidance they ‘were not able to monitor the spread of the injectate through the foramen, if any, into the epidural space (because of the bony dropout artifact of the transverse process)’.47 The term nerve root block or selective nerve root block has historically been used to reference a highly selective procedure in which a single specific nerve root is anesthetized to confirm or refute it as the source of pain.55 56 Although they did not use US guidance or ideal injection volumes, Anderberg et al found 60% correlation between selective diagnostic nerve root blocks (SNRBs) and magnetic resonance imaging (MRI) pathology; however, correlation between SNRB and neurological deficits/radicular dermatome distribution was 28%.57 The same group found that group mean visual analog scales were reduced 86% for arm pain and 65% for neck pain.58

    A recent case series used the term “US-guided cervical transforaminal epidural steroid injection”, when studying epidural spread using US-guided needle position at the foraminal edge (with epidural spread confirmed via FL imaging).59 Even in the experienced hands of the proceduralists 1/15 injections (0.067; 95% CI: <0.0001 to 0.3184) did not display epidural flow.59 More importantly, if the procedure was conducted without FL confirmation, aspiration was the only means proposed by the authors to confirm no VP and/or injection. As the poor reliability of aspiration has been well demonstrated for transforaminal injections (sensitivity, 45.9%), using US guidance without FL guidance is cautioned against as vascular flow and/or IVI cannot be ruled out for transforaminal or interlaminar injections.60–66

    The majority of studies proposing US-guided injections use a needle position that differs from an FL-guided injection. For US-guided cervical nerve root injections, the target is in the intertubercular neural groove situated between the nerve root and the posterior tubercle, which is outside of the neuroforamen.47 67–69 Hence, given the positioning of the needle in US-guided injections and the current evidence of inconsistent epidural flow, the authors strongly caution against the inappropriate designation of US-guided injections as CTFEI, as the epidural spread cannot be confirmed without FL imaging.

    Detection of vasculature for US guidance versus FL guidance

    A major proposed benefit of US-guided versus FL-guided cervical injections is the theoretical risk reduction of puncturing a critical vessel in the posterior aspect of the intervertebral foramen communicating with the anterior spinal artery.51 70 The basis of this benefit stems from the premise that US allows for real-time visualization before needle puncture, while puncture is only recognized after the fact with arterial flow of contrast agent with fluoroscopy and digital subtraction imaging (DSI).47 52

    To date, there are no adequately powered studies to assess the reliability of US guidance in detecting vulnerable vessels. In theory, US evaluation may be specific, but it may lack sufficient sensitivity for identifying vulnerable vessels when performing cervical injections. Indeed, US studies still rely on contrast injection during live FL observation to rule out IVI prior to depositing injectate and have produced mixed results in the rates of vascular injection.71–73 Wakeling et al studied 149 consecutive patients, with the majority of injections at C6 and/or C7 (81%; 122/151) and found no complications. The authors reported a 72% (107/149) initial positive response to injection using combined FL-guided/US-guided cervical nerve root injections. Moreover, they reported an average dose area product of 0.54 Gycm2, which approximates to 0.135 mSv, reducing radiation exposure from fluoroscopy only, estimated to be 0.64 mSv and CT-guided injections estimated between 0.54 and 1.1 mSv.73 While there is a modest reduction in radiation exposure, it should be noted that studies implementing US are limited to those with relatively low body mass indexes as visualization of radicular arteries may be challenging in obese patients.71 One major limitation of studies using intermittent fluoroscopy in combination with US71 is that intermittent FL images miss 57% of vascular injections,74 which may explain why IVI is identified at a lower rate during the FL and US combination approach versus live fluoroscopy. Indeed, Jee et al cautioned against relying on US to confirm the absence of critical vessels that are small in size.71

    Even though it has been suggested that US prevents IVIs,47 52 Park et al reported 5 injections in which blood was aspirated in the US group versus 0 in the FL group.75 Moreover, even without any aspiration of blood seven patients demonstrated intravascular contrast spread after live fluoroscopy, which raises the question as to how many US-guided injections in clinical practice may encounter intravascular contrast spread if fluoroscopy is consistently used in conjunction with US. The inconsistent correlation of positive aspiration with intravascular flow on fluoroscopy75 highlights the shortcoming of US, as its method of confirmation is aspiration which has been shown to have insufficient sensitivity.60–66

    The advantage of US over FL guidance, in regard to VP remains to be proven. In a study comparing US guidance to FL guidance, Park et al found no statistical difference in the frequency of IVIs between US guidance and FL guidance.76 This result was also confirmed in their randomized controlled trial where no statistically significant difference was observed between the US-guided and FL-guided approach.71 This may be due to the fact that proper FL-guided technique, in practice and in research, calls for review of MRI imaging when planning needle approach prior to the FL-guided injection which allows for visualization of potential vessels. It would be interesting to study the sensitivity and specificity of MRI imaging and or CT imaging versus that of US in identifying vessels.

    Although the US literature appropriately recommends the ‘careful evaluation of vulnerable vessels around the cervical NR with US before the procedure’ to avoid VP and/or injection.59 The issue is with vessels that cannot be visualized by US guidance as ‘…confirmation of the absence of critical vessels that are small in size may still be impossible with the current US technology. Despite real-time monitoring of the injections, US may not reliably detect microscopic IVIs that may lead to neurological injury’.75 Narouze et al appropriately emphasized the limitation of the US-guided approach, stating ‘the inability to visualize critical vessels at the posterior aspect of the neuroforamen…does not necessarily mean they do not exist…ultrasonography may not reliably detect tiny IVIs that still can lead to neurologic injury’.47 This issue is highlighted by angiography demonstrating the complex arterial network of the cervical spine (figures 3 and 4). Hence, as is well documented in the literature investigating and reviewing US guidance, not detecting vessels does not ensure the absence of these vessels.71 72 75 Therefore, although US may assist in avoiding IVI, it cannot detect and/or rule out such injections if they occur.71 75 In procedures implementing FL guidance, MRI is sufficient to detect the large vessels identified with US guidance. However, FL guidance has the advantage of not only identification of variations in large vessel anatomy (with prior MRI review), it has the added benefit of detecting inadvertent flow in vessels not well visualized on MRI or US.

    Figure 3
    Figure 3

    Cervical arterial supply. The cervical anterior spinal system and the complex network of cervical vessels, bilateral vertebral, occipital, anterior cervical, deep cervical, and ascending pharyngeal, which pose significant safety risks during cervical injections. Most of these connections are relevant in terms of vertebral artery anastomoses. Illustration of these connections in a patient with a hypoplastic vertebral artery, where the diagnostic catheter is occlusive at the origin and therefore allows for reflux into adjacent vessels. (Images reproduced with permission from http://neuroangio.org, and for which http://neuroangio.org holds copyright.)

    Figure 4
    Figure 4

    Digital subtraction images of the complex network of cervical vessels. Red arrow—anterior spinal; white arrow—radiculomedullary; yellow arrow—epidural arcade; purple arrow—odontoid arcade; blue arrow—muscular branch ascending pharyngeal; black arrow—neuromeningeal trunk, ascending pharyngeal; orange arrow—pharyngeal trunk, ascending pharyngeal; green arrow—occipital; pink arrow—deep cervical; brown arrow—ascending cervical. (Images reproduced with permission from http://neuroangio.org, and for which http://neuroangio.org holds copyright.)

    Conclusions

    There is a paucity of information to be used for evidence-based recommendations and standards for clinical practice regarding the safety of US guidance for cervical epidural injections. Given the increased utilization of US-guided injections in interventional spine procedures there needs to be a call for increased prospective cohorts and randomized controlled trials into the accuracy, safety and efficacy of the technique. This is especially true for high-risk injections such as injections intended for the epidural space.

    US guidance provides good soft tissue and bony visualization and may be useful for superficial axial injections. However, it remains unproven for epidural injections due to the major shortcomings of limited resolution of deep structures, inability to rule out IVI and spread of the injectate into the foramen and epidural space. Based on our evaluation of the literature, US-guided cervical spine procedures to treat cervical radiculitis remains a ‘partially blind technique’,51 and there is still a need for adequately powered studies evaluating its safety, accuracy, and effectiveness.

    FL guidance and DSI have better evidence than US guidance for cervical transforaminal epidural steroid injections or cervical selective nerve root blocks to treat cervical radiculitis. If US guidance is planned, until higher level evidence is available, it is recommended to combine it with FL guidance. If FL confirmation is not possible, the proceduralist should clearly discuss with patients that evidence in support of the accuracy, effectiveness and safety of US-guided cervical injections is limited and may not be equal to injections using guidance from other modalities. More importantly, the risk profile of US-guided injection should be clearly explained, including spinal cord injury, the inability to confirm epidural spread and the inability to rule out intravascular flow.

    Limitations

    This review is an overview of the most pertinent studies of US guidance in the treatment of cervical radicular pain, and therefore prone to a higher degree of bias when compared with a meta-analysis.77 78 We attempted to reduce bias through appropriate writing and research techniques79–83 as well as involving the Health Sciences Informationist at Eskind Biomedical Library, Vanderbilt University to conduct the final database review in search of the relevant literature.

    Data availability statement

    Data analyzed in this study were a re-analysis of existing data, which are openly available at locations cited in the reference section. Further documentation about data processing is not applicable.

    Ethics statements

    Ethics approval

    If applicable, the authors state that they have obtained appropriate institutional review board approval or have followed the principles outlined in the Declaration of Helsinki for all human or animal experimental investigations. In addition, for investigations involving human subjects, informed consent has been obtained from the participants involved.

    Acknowledgments

    The authors would like to thank Ms. Heather E Laferriere, MLIS (Master of Library and Information Studies), Health Sciences Informationist, Eskind Biomedical Library at Vanderbilt University for her help in the database review for relevant literature.

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    Footnotes

    • Contributors RE and BJS: Formal analysis; Methodology; Project administration; Visualization; Writing - original draft; Writing - review & editing. DJK and EK: Project administration; Writing - original draft; Writing - review & editing.

    • Funding All authors declare that they have no financial and personal relationships with other people or organizations that could inappropriately influence (bias) their work. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

    • Competing interests None declared.

    • Provenance and peer review Not commissioned; externally peer reviewed.