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Abstract
Background While fluoroscopic guidance is currently the imaging standard for cervical medial branch blocks (CMBBs), ultrasound guidance (USG) offers several potential safety advantages such as real-time needle visualization and the ability to detect and avoid critical soft tissue vascular or neural structures. However, no large-scale trials have examined the safety of USG for CMBB.
Methods Five hundred patients undergoing 2308 individual block levels were recruited using a prospective cohort design, and blocks were performed in an outpatient office setting using an in-plane USG technique. Primary outcomes included immediate block-related complication, as well as delayed occurrences, in the following 2 weeks. Vascular structures adjacent to the target area, as well as the occurrence of vascular breach, were recorded.
Results Three minor immediate complications were noted (two subcutaneous hematomas, one vasovagal reaction) comprising 0.13% of blocks (0.03% to 0.38%; 95% two-sided CI), and no delayed events were recorded (0% to 0.16%; 97.5% one-sided CI). Blood vessels were detected and avoided in 8.2% of blocks, and vascular breach was noted in 0.52% of blocks (0.27% to 0.91%; 95% two-sided CI).
Conclusion When performed using an in-plane technique by experienced operators, USG CMBB was found to be safe, with rare minor immediate complications and no further adverse event reported in the following 2 weeks.
Trial registration number NCT04852393.
- Nerve Block
- COMPLICATIONS
- CHRONIC PAIN
- Neck Pain
- Ultrasonography
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information.
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, an indication of whether changes were made, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
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WHAT IS ALREADY KNOWN ON THIS TOPIC
The value of ultrasound guidance (USG) for cervical medial branch block using an in-plane technique has previously been examined and found to provide similar accuracy with shorter performance times when compared with fluoroscopy.
However, the safety of this novel technique has not been assessed.
WHAT THIS STUDY ADDS
USG was associated with rare minor short-term complication and may reduce the incidence of vascular breach when compared with fluoroscopy.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
This study reinforces the value of USG as an alternative to fluoroscopy in clinical practice.
Introduction
Cervical medial branch blocks (CMBBs) are commonly used for the diagnosis and management of facet-related pain.1 The latter constitutes the most important cause of axial neck pain and has been implicated in 40% of all cases.2 In addition, the upper cervical joints can also cause cervicogenic headaches, an often-debilitating condition representing up to 20% of chronic headaches.3 Well-defined pain referral patterns for each joint can help operators select the appropriate injection level.4 5 Fluoroscopy has long been the imaging standard for spinal procedures as it allows operators to reliably define bony structures while remaining impervious to the depth of overlying tissue.6 Nonetheless, several anatomic features unique to the neck offer an ideal canvas for ultrasound guidance (USG). For instance, cervical targets are relatively shallow (usually ≤3 cm under the skin surface): this falls within the range of high-resolution linear array probes. Another particularity of the cervical spine stems from the large number of critical soft tissue structures (blood vessels, nerves) in close proximity to the needle path. Unlike fluoroscopy, USG allows the operator to visualize and avoid these structures during needle insertion when using an in-plane technique, which may reduce complication rates related to vascular breach.7–9 Several clinical trials have found that USG can provide similar accuracy to fluoroscopy10 11 and recent multisociety consensus guidelines have supported its use as a possible alternative to latter.12 However, larger studies documenting safety-related data are lacking. In this prospective observational study, we therefore sought to examine the frequency of immediate and delayed complications associated with this technique when used in an outpatient office setting.
Material and methods
This trial was registered at ClinicalTrials.gov (Study ID: NCT04852393) on April 21, 2021 prior to patient recruitment. Ethics committee approval 2020-21-105-H (Interior Health Research Ethics Board) was also secured prior to patient enrollment which began on May 5, 2021. The current report reviews the safety-related data that were collected as the primary outcome of a protocol that also examined analgesic and functional outcomes. In addition, the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) checklist for cohort studies was followed during the writing of this manuscript.13
After obtaining written and informed consent, consecutive patients undergoing CMBBs were recruited from the clinical practice of four physicians working in a tertiary level pain clinic. Patients were selected for CMBB based on typical clinical presentations, which included pain on combined extension and rotation, as well as tenderness on palpation over the affected joints. In addition, previously documented referral patterns for each joint were used to determine the levels to be treated.4 5
Inclusion criteria were age over 18 years with a pain intensity of at least 5/10 (at rest or on movement) and a pain duration of at least 4 months. Exclusion criteria were inability to communicate or complete follow-up questionnaires; known bleeding disorder or coagulopathy; patients on antiplatelet medication other than aspirin and those on anticoagulants (coumadin, AT III agents); inability to visualize targeted structures on ultrasound; presence of acute radiculopathy or new onset neurological symptoms in the upper extremities; patients with bilateral neck pain if only one side was treated.
CMBBs were performed in an office setting, within a facility where advanced resuscitation equipment and drugs were available. In addition, patients were asked to be accompanied by a responsible adult following discharge and no prior fasting was required. Following the blocks, patients were observed for a 10-minute period and those deemed not ready for discharge after this period were transferred to a monitored recovery room area. All patients were advised to expect balance problems following the injections and minimize ambulation during this time. Patients with pre-existing mobility problems (walker, cane) were escorted out of the facility in a wheelchair.
All blocks were performed by four of the coauthors who were experienced operators (JPE, RJF, JV, FDV), having previously performed CMBBs on at least 200 individual patients prior to the commencement of the study. The technique employed has previously been described10 11 14 15 and the following provides a summary description: patients were positioned in the lateral decubitus position, and following skin disinfection, the probe was placed on the lateral surface of the neck; a prescan in the transverse plane using color Doppler was then performed to identify any vessels lying in the needle trajectory7 (figure 1); once the target articular pillar (C3-C6 MBB), C2-3 joint (TON) or C7 superior articular process (C7 MBB) was identified, a needle was placed using a transverse scan and continuous in-plane visualization (figure 2); a long-axis (coronal) scan was then undertaken to confirm appropriate needle positioning and any required adjustments made (figure 3); the injection was then performed under continuous visualization in the transverse plane, with minor adjustment made as required to ensure spread of the injectate along the periosteum, below the semispinalis capitis muscle (figure 2). A 22-gauge 70 mm or 25-gauge 50 mm needle (Henke, Tuttligen, Germany) was used as per the operator’s preference and the injectate was 1% lidocaine (Teligent, Mississauga, Canada). Volumes injected were 0.3 mL for levels C3-C6, 0.6 mL for C7 and 0.9 mL for the TON). In addition, the needle was aspirated for the presence of blood prior to injection and tissue expansion noted to confirm appropriate injectate spread. Scanning was performed with a Sonosite PX or X-Porte (Fujifilm Sonosite, Bothell, Washington, USA) using a 15-4 or 15-6 MHz linear probe.
Transverse sonographic scan at the level of the C7 superior articular process (C7 SAP) recorded during a C7 medial branch block, demonstrating a needle that has been advanced below an intervening artery, avoiding a vascular breach. Lower explanatory insets demonstrating surface probe placement, scan line on a squelettal model and an annotated line drawing. Art, artery; C7 SAP, C7 superior articular process; N, needle.
Transverse sonographic scan at the level of C4 demonstrating an in-plane needle place on lateral surface of the articular pillar. Lower explanatory insets demonstrating surface probe placement, scan line on a squelettal model and an annotated line drawing. AP, articular pillar; N, needle; SSC, semispinalis capitis muscle.
Long-axis (coronal plane) sonographic scan along the cervical articular pillars, demonstrating a needle tip on the articular pillar of C4 following an injection of local anesthetic. Lower explanatory insets demonstrating surface probe placement, scan line on a squelettal model and an annotated line drawing. Articular pillars (C3, C4, C5); facet joint lines (*); N, needle.
Data collection
Patient demographic data (age, body mass index (BMI)) and block-related data (needle size, levels treated) were recorded. In addition, the occurrence of paresthesias or vascular breach (as defined by the appearance of blood in the needle hub during placement or on aspiration prior to injection) was also recorded. Operators also reported the presence of blood vessels adjacent to the articular pillars noting the levels involved. Other immediate complications such as vasovagals, local anesthetic toxicity (dizziness, tinnitus, altered level of consciousness, seizure) or other unexpected neurorological symptoms (nerve root block) were also noted.
Following discharge, patients were provided with a follow-up form that was to be returned 2 weeks following the injections. This form listed possible complications occurring in the 2 weeks following discharge that should be reported: redness/swelling/skin bruising at the injection site, lump in the neck (hematoma), any neurological symptoms (new onset radicular pain, numbness, weakness or paresthesia in upper extremities). If patients had any other concerns following the blocks, they were encouraged to report them on the form. In addition, if any complications were noted, patients were asked to immediately contact the clinic. Patients not returning the sheet were contacted by their physician or a research assistant.
Following the recruitment of 250 patient, an interim review of additional patient concerns found frequent reports of balance problems referred to as “dizziness” in the immediate post block period. CMBBs are known to be associated with transient balance problems, and as such, this phenomenon was not included in the list of complications. Nevertheless, because of the lack of existing data on this side effect, it was decided to systematically examine it in the remaining cohort.
Statistical analysis
When considering the optimal sample size for our study, we determined that 500 individual patients would provide a sufficient number of blocks to detect rarer complications and provide an acceptable CI when reporting our findings. Thus, no occurrences of an event (0%) in 2000 blocks provides an upper bound of 0.18% using a one-sided 97.5% CI. Descriptive statistics were used to present demographic and complication-related data. CIs for binomial proportions were calculated using the Clopper-Pearson method (web-based tool https://statpages.info/confint.html).
Results
A total of 500 consecutive consenting patients undergoing 2308 individual blocks were recruited between May 5, 2021 and October 1, 2023 (figure 4). Demographic and block-related data are presented in table 1. In addition, 43 patients were over the age of 75 and 124 had a BMI over 30 (14 of those were over 40). Complication-related data are presented in table 1: immediate events occurred in 3 (0.6% of patients) and included two subcutaneous hematomas (less than 1 cm in diameter), as well as one vasovagal reaction without syncope, which did not require intravenous access. These patients were discharged without incident following an additional observation period of 10 min. Data for delayed complications were available on all patients and no occurrences were reported at 2 weeks. Data on the presence and duration of post-block balance problems were available for 235 patients and 59.1% reported the presence of these symptoms with a median duration of 45 min (IQR 92.5). In addition, 66% of C2/C3 (TON) blocks and 78% of bilateral procedures (vs 50% for unilateral) reported these symptoms.
Patient flow chart.
Results
Discussion
In this prospective cohort study, we found that USG CMBB was associated with the rare occurrence of minor immediate post-block complications and no further adverse events were reported during the 2-weeksfollow-up period. Several technical factors may have contributed to these reassuring finding. First, we used an in-plane approach that allows the needle to be continually visualized during placement, thus reducing the risk of damage to neurovascular structures. Second, the posterolateral insertion site associated with the in-plane approach results in a needle angle that is closer to that of the sagittal plane, making an errant needle less likely to accidentally enter the neural foramen. Third, a preprocedural color Doppler scan was performed to detect any vascular structures in the projected needle path, thus reducing the risk of vascular breach. And finally, 1% lidocaine was used as the injectate to reduce the risk toxicity in the event intravascular injection or unintended neural spread. Further, lidocaine has been found to provide a similar therapeutic effect when compared with bupivacaine16 and the addition of steroids has not been shown to provide additional benefit when performing cervical medial branch blocks.17
As of the time of writing this text, the current literature contains one published case report of a serious complication following an USG CMBB involving an attempted C7 MBB using an out-of-plane (OOP) approach that resulted in a spinal cord injury.18 Although early descriptions of USG CMBB examined an OOP approach in healthy volunteers,19 this technique raises several possible safety concerns. Indeed, in addition to the needle tip not being visualized during placement, the insertion angle follows the coronal plane, potentially increasing the risk of foraminal penetration and neural injury (figure 5). This hazard is greater in the lower cervical segments where targets are at greater depths and smaller (C7 superior articular process).
Annotated squelettal model of a cervical verterbra viewed in the tranverse plane, demonstrating the angles of approach seen during a cervical medial branch using the in-plane (IP) and out-of-plane (OOP) approach. AP, articular pillars; AT, anterior tubercle; Lam, lamina; PT, posterior tubercle of transverse process; VB, vertebral body.
One of the advantages of USG when compared with fluoroscopy lies in its ability to detect and avoid arteries adjacent to targeted areas.20 Indeed, in addition to larger branches of the deep and ascending cervical arteries, smaller ones (mean diameter 1.25 mm) have been found to cross the lateral aspect of the facet column.7 In this current study, operators were asked to report blood vessels in the path of the intended needle trajectory, and their distribution and frequency (5.9% to 11.8%) mirror those of a previous ultrasound imaging-based survey.7
Published studies examining the incidence of vascular breach in the context of fluoroscopy-guided medial branch block found a higher incidence in the cervical spine when compared with the thoracic levels and lumbar levels, suggesting a possible advantage for the use of USG.8 9 Indeed, we found a per block occurrence of 0.52%, notably lower than the findings reported by Verrills et al8 and Manchikanti et al9 (3.9% and 3.3%, respectively). In addition, our incidence of hematoma (0.09%) was lower than previously reported by Manchikanti et al (0.37%).
However, comparisons to fluoroscopy are speculative, as our study was designed to examine the safety of USG when used as a single imaging modality for CMBB and this precluded the use of live fluoroscopy or digital subtraction angiography (DSA) to exclude intravascular injection. Therefore, we relied on needle aspiration and the appearance of blood in the needle hub to detect vascular breach, which may have underestimated its incidence. Indeed, when examined in the context of spinal injections, this approach has been found to have a high specificity but low sensitivity (34.1–45.9%) when compared with real-time contrast injection under fluoroscopy.21–23 It should be noted however that the previously discussed fluoroscopy-based CMBB studies used static (spot) fluoroscopic imaging (Verrills et al) or no contrast (Manchikanti et al), strategies that may have similarly underestimated the incidence of vascular breach, when compared the current imaging standards of live fluoroscopy or DSA.24
Transient balance problems following CMBB have previously been described in the context of TON blocks and is a side effect that is likely familiar to clinicians performing these procedures.1 Indeed, we found that a majority of patients reported this problem (59.1%), which was more common when the C2/C3 level was targeted (66%). The largest proportion, however, was found in patients undergoing bilateral procedures (78%). While the mechanism underlying this block-related phenomenon has yet to be determined, it could be speculated that the injected local anesthetic transiently affects the cervical proprioceptive system, either directly by blocking the medial branches, or secondarily by spread to adjacent muscles.25 26 Although this side effect was transient (median duration 45 min), it could increase the risk of falls following discharge, particularly in older individuals or those with pre-existing walking problems. However, this problem was not observed in our cohort, likely because patients were asked to be accompanied and minimize ambulation in the post-block period.
Various forms of bias can affect the validity of cohort studies, with selection and information bias being significant concerns. We endeavored to minimize them by including a large sample size and recruiting consecutive consenting patients. The resulting demographics (older subjects with higher BMI) is representative of the daily practice at our clinic and not one that could be expected to minimize the risk of complications. In addition, we employed a prospective design with trial registration and ensured a complete dataset for complications related outcomes, with no follow-up losses.
When considering the generalizability of our findings, it should be noted that the blocks were performed by physicians with significant experience in USG CMBB, a factor that may have minimized the occurrence of complications. While the number of cases necessary to achieve proficiency in the cervical spine has not been determined, a study examining USG lumbar medial branch blocks determined that approximately 62 successful cases were required.27 Another point that should be considered is that our recruitment criteria excluded anticoagulated patients, a decision that was made because of the lack of consensus regarding the optimal management of this group at the time the study protocol was conceived. Although one could speculate that the lower incidence of vascular breach associated with USG could be particularly advantageous in anticoagulated patients, further research would be required to validate this theory.
Conclusion
In this prospective cohort study, we found that USG CMBB using an in-plane technique was associated with the rare occurrence of minor block-related complications, with no further adverse events noted after a 2-week follow-up period. In addition, although we found a lower incidence of vascular breach than has previously been reported with fluoroscopic guidance, further studies using a comparative design would be required to examine this issue.
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information.
Ethics statements
Patient consent for publication
Ethics approval
This study involves human participants and was approved by ethics committee approval 2020-21-105-H (Interior Health Research Ethics Board). Participants gave informed consent to participate in the study before taking part.
References
Footnotes
Contributors J-PBE, RJF, JV, and FDV participated in the planning, conception, design, conduct, reporting, acquisition of data, data analysis, and interpretation of data. JPE, RW, and AW participated in the reporting, acquisition of data, data analysis, and interpretation of data. RJF is the guarantor and is responsible for the overall content.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.