Ultrasound-Guided Cervical Nerve Root Block: Does Volume Affect the Spreading Pattern?

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1 Pain Medicine 2016; 17: doi: /pm/pnw027 SPINE SECTION Original Research Article Ultrasound-Guided Cervical Nerve Root Block: Does Volume Affect the Spreading Pattern? Seok Kang, MD, Seung Nam Yang, MD, PhD, Se Hwa Kim, MD, Chan Woo Byun, MD, and Joon Shik Yoon, MD, PhD Department of Physical Medicine and Rehabilitation, Korea University Guro Hospital, Seoul, Korea Correspondence to: Joon Shik Yoon, MD, PhD, Department of Physical Medicine and Rehabilitation, Korea University Guro Hospital, 148, Gurodong-ro, Guro-gu, Seoul, Republic of Korea. Tel: ; Fax: ; Funding sources: No financial support was received. Conflicts of interest: There are no conflicts of interest to disclose. Abstract Objective. Ultrasound-guided cervical nerve root block (US-CRB) is considered a safe and effective method for the treatment of radicular pain. However, previous studies on the spreading pattern of injected solution in US-CRB have reported conflicting results. The aim of this study was to investigate the spreading pattern in relation to injection volume. Design. An institutional, prospective case series. Setting. A university hospital. Subjects. Fifty-three patients diagnosed with monoradiculopathy in C5, 6, or 7. Methods. US-CRB with fluoroscopic confirmation was performed. After the cervical roots were identified in ultrasound imaging, a needle was gently introduced toward the posterior edge of the root using an in-plane approach. The spread of 1 ml and 4 ml contrast medium, each injected in the same needle position, was examined with anteroposterior and lateral fluoroscopic views. After contrast injection, a mixture of local anesthetic and corticosteroid was injected. Clinical outcome was assessed using a numeric rating scale before and 2 weeks after the procedure. Results. Contrast medium did not spread into the epidural space in any patients with 1 ml contrast medium injection, but it did spread into the intraforaminal epidural space in 13 patients (24.5%) with 4 ml. Pain improved in all patients. There was no significant difference in pain relief according to the spreading pattern. Conclusion. The spreading pattern of injected solution in US-CRB could be partially affected by the injectant volume. However, further studies are needed to assess the importance of other factors, such as needle position and physiological effects. Key Words. Ultrasound; Cervical; Selective Nerve Root Injection; Radiculopathy; Spreading Pattern Introduction Cervical transforaminal steroid injection (C-TFSI) is being increasingly utilized for the management of radicular pain caused by cervical disc disorders [1,2]. It is generally performed under fluoroscopy or computed tomography guidance [3,4]. However, C-TFSI carries a potential risk of severe complications, such as brain stem and spinal cord infarction due to accidental intravascular injection into the radicular or vertebral artery, because the fluoroscopy or computed tomography is not able to visualize small vessels [5 7]. In contrast, high-resolution ultrasound (US) can be used to identify the target nerve and neighboring vessels [8,9]. Additionally, US has the advantage of being free of radiation. Therefore, US-guided cervical nerve root block (US-CRB) is accepted as a safe and effective alternative method for the treatment of upper extremity radicular pain [10]. When performing US-CRB, the target of the needle is the intertubercular groove outside of the cervical VC 2016 American Academy of Pain Medicine. All rights reserved. For permissions, please journals.permissions@oup.com 1978

2 Volume Effect on Spreading in US-CRB foramen [11]. Since it is unclear whether the injected solution spreads into the intraforaminal epidural space, the indications of US-CRB are relatively limited. Previous studies have reported that, although US-CRB provides effective pain relief, the injected solution spreads in an extraforaminal direction [12]. In contrast, other researchers have reported intraforaminal spreading [11,13]. It could be hypothesized that these different spreading patterns are affected by two factors: the position of the needle tip and the volume of the solution. In fluoroscopy-guided C-TFSI, the spreading pattern is known to be related to the injected volume [14]. Therefore, as a feasibility study of the spreading pattern of injected solution in US-CRB, we primarily aimed to investigate the spreading pattern change in relation to the volume of solution injected while controlling the needle position. Methods Participants This study was comprised of consecutive case series. We prospectively recruited 53 patients diagnosed with mono-radiculopathy in C5, 6, or 7 by clinical history, cervical magnetic resonance imaging (MRI), and electrophysiological examination who underwent cervical nerve root injections using US as the primary imaging tool with fluoroscopic confirmation. Each patient complained that the radicular pain in the upper extremity persisted for at least 2 months, despite appropriate medication and conservative treatment. In all patients, foraminal stenosis was indicated on the MRI scan due to disc protrusion or degenerative uncovertebral joint hypertrophy. There were 38 patients with disc protrusion and 15 patients with uncovertebral hypertrophy. The MRI finding was correlated with the symptom in each patient. In addition, electrophysiological examinations were performed for all patients. Thirty-nine patients showed positive findings correlated with their symptoms; however, 14 patients had negative findings in the eletrophysiological examination. The level of procedure was determined by the combination of clinical symptoms, MRI findings, and electrodiagnosis in each of the patients. General baseline characteristics, such as age, sex, height, weight, body mass index (BMI), and duration of symptoms, were recorded. Patients were excluded if they were younger than 18 years, older than 80 years, or pregnant. Other exclusion criteria were as follows: a) cervical radiculopathy at multiple levels, b) cervical myelopathy, c) systemic inflammatory disease, d) uncontrolled diabetes, e) prior allergic reaction to lidocaine or contrast media, f) injections within prior 3 months, and g) recent cervical spinal surgery. No pain medications that the patients had been taking before the study were discontinued. However, additional pain medication was not allowed during the study. The Institutional Review Board of Korea University Guro Hospital approved this study, and written informed consent of all patients was obtained. Procedure US-CRB was performed according to a modified Narouze et al. technique [8,11]. During the procedure, patients were positioned in the oblique supine decubitus position with head turned approximately 15 to the opposite side. The angle of the C-arm was adjusted to obtain the adequate anteroposterior and oblique views of the cervical spine. After aseptic skin preparation, a 12- MHz linear transducer of a US machine (Philips Ultrasound Inc., Bothell, WA, USA) was applied to the symptomatic side of the neck in the transverse plane. Initially, the cervical spinal level was determined by identifying the transverse process. The C7 transverse process was identified by the shape of the transverse process, rudimentary anterior tubercle, and prominent posterior tubercle. The C6 transverse process was characterized by its sharp anterior tubercle. The C5 transverse process was identified by the two-humped camel sign formed by anterior and posterior tubercles. Within the intertubercular groove of the corresponding transverse process, the nerve root of each cervical spinal level was observed with hypoechoic texture. We identified the targeted nerve root of each patient by moving the transducer cranially from the C7 level. After the targeted nerve root was identified, a 60-mm, 23-G needle (Korea vaccine Co., Seoul, Korea) was gently introduced toward the posterior edge of the nerve root under real-time US guidance. The needle was inserted just lateral to the transducer and advanced, from posterolateral to anteromedial, with an in-plane approach. The needle tip was placed between the nerve root and posterior tubercle outside of the intervertebral foramen and approached close to the epineurium. To prevent inadvertent injection to the vessel, the location of the vessels around the nerve root was confirmed with color Doppler (Figure 1). Once the needle tip was positioned, 1 ml contrast medium (Omnipaque-240, GE Healthcare, Princeton, NJ, USA) was slowly injected. While maintaining the needle in the same position, the spreading pattern of the contrast medium was visualized with fluoroscopy immediately after injection. An additional 3 ml contrast medium was then injected, and fluoroscopic examination was repeated at the same needle position. After examination of the spreading pattern, 2 ml 0.5% lidocaine with 2 ml (10 mg) dexamethasone was injected. Outcome Measurements The spreading pattern was classified into two categories: 1) extraforaminal, non-epidural spreading, where the injected contrast does not reach the neural foramen and spreading laterally to the midline of aricular pillars in pheripheral direction; and 2) intraforaminal, epidural spreading, where the injected contrast extends beyond the neural foramen and observed medially to the midline of the articular pillars. (Figure 2). The evaluation of the spreading pattern was conducted by one blinded 1979

3 Kang et al. Figure 1 (A) Axial transverse ultrasound image showing sharp anterior tubercle of C6 transverse process (C6 TP). (B) Axial transverse ultrasound image of C7 transverse process (C7 TP); there is only one posterior tubercle. (C) Axial ultrasound imaging of C6 nerve root block. Solid arrows point to the needle. The needle tip was placed between the nerve root and posterior tubercle; the needle was placed at this position in all the procedures. (D) Axial transverse ultrasound image with color Doppler showing a small vessel (solid arrow) around the nerve root. N ¼ nerve root; CA ¼ carotid artery; pt ¼ posterior tubercle; at ¼ anterior tubercle. examiner who had over 10 years of experience in the spinal procedure. The severity of radicular pain was assessed using the numeric rating scale (NRS) from 0 (no pain) to 10 (severe pain). NRS scores before and after the US-CRB were compared in order to evaluate the efficacy of the procedure. Assessment of the outcome was performed before and 2 weeks after the procedure by the other investigator, who was blind to the results of the spreading pattern. To compare the clinical efficacy according to the spreading pattern, the percentage of pain relief was calculated using the following formula: ðpre-treatment pain score post-treatment pain scoreþ 100=pre-treatment pain score: If patients showed more than a 50% reduction in their NRS score, the result of the procedure was considered successful. Data were analyzed using IBM SPSS statistics version 20. A chi-squared test was used for the analysis of the spreading pattern in relation to the injection volume and the comparison of success rate according to the spreading pattern. A Wilcoxon signed rank test was performed to compare pain severity before and after the US-CRB, and a Mann Whitney U test was performed to compare pain relief after 2 weeks according to the spreading pattern. Results Subject Characteristics The average age of the patients was years. Of the 53 patients, 27 were men and 26 were women. The US-CRB was performed at the C5 level in one patient, the C6 level in 30 patients, and the C7 level in 22 patients. Eighteen patients underwent the procedure on the right side and 35 patients on the left side (Table 1). Spreading Patterns of Contrast Medium The contrast medium clearly spread along the nerve roots in all patients. It did not spread into the epidural space in any patients with 1 ml injected contrast medium, but it did spread into the intraforaminal epidural 1980

4 Volume Effect on Spreading in US-CRB Table 1 Patient characteristics Characteristic Patients (N ¼ 53) Age (Mean 6 SD, years) Sex (Men:Women) 27: 26 Height (cm) Weight (kg) Body mass index Duration of symptom (months) US-CRB a performed at C5 (Right:Left) 1 (0:1) US-CRB performed at C6 (Right:Left) 30 (11:19) US-CRB performed at C7 (Right:Left) 22 (7:15) a US-CRB ¼ ultrasound-guided cervical nerve root block. Figure 2 Schematic illustration describing spreading pattern of contrast medium. Black arrow: site of contrast injection. Intraforaminal epidural spreading was defined as the contrast extending beyond midline (dotted line) of articular pillars. space in 13 patients (24.5%) with 4 ml injected contrast medium (Figure 3). The one patient who underwent US-CRB at the C5 level showed intraforaminal spreading. In 6 of the 30 patients (20.0%) who had the procedure at the C6 level, the injectant spread in an intraforaminal direction. Similarly, in 6 of the 22 patients (27.2%) who had the procedure at the C7 level, intraforaminal spreading occurred (Table 2). Among the 38 patients with disc protrusion, 10 patients (26.32%) showed an intraforaminal spreading pattern. Among the 15 patients with uncovertebral hypertrophy, 3 patients (20%) showed an intraforaminal spreading pattern. No significant difference was observed in the spreading pattern according to the diagnosis (p > 0.05). In addition, there was no significant difference in general patient characteristics in relation to the spreading pattern (p > 0.05). Clinical Outcome The mean pain score before the US-CRB procedure was (median: 4; interquartile range: 4 5). In all patients, pain significantly improved after the procedure; the mean NRS score decreased to (median: 2; interquartile range: 1 2, p < 0.05). Of the 53 patients, 50 reported more than 50% pain relief (success rate: 94.3%, confidence interval: %). All patients who showed an intraforaminal spreading pattern with 4 ml contrast injection reported pain reduction. However, the success rate was not significantly different according to the spreading pattern. The accuracy of intraforaminal contrast spread did not affect the short-term outcome (p > 0.05, Table 3). Discussion Radicular pain of the upper limb caused by cervical disc disorder is managed by cervical epidural steroid injection [15,16]. The epidural steroid injection reduces inflammatory edema of injured nerve roots, reduces sensitization of dorsal horn neurons, and suppresses the transmission of nociceptive C-fibers [16]. The methods for epidural injection include interlaminar and transforaminal approaches. Recently, US-CRB has been used as an alternative to fluoroscopy-guided C-TFSI because US can visualize the vascular structure and does not involve radiation exposure [8 10]. The objective of US-CRB is the nerve root outside of the cervical foramen. However, intraforaminal spreading of the injected solution could affect the efficacy of the procedure [5,17,18]. If the injected solution were to spread close to the target nerve root or dorsal root ganglion, the clinical outcomes would improve. In fluoroscopy-guided C-TFSI, the intraforaminal spread is related to the injected volume [14]. Recent studies on the spreading pattern of injected solution in US-CRB have produced conflicting results. Yamauchi et al. found that injection of 1 ml contrast medium in US-CRB led to the spread of the injectant mainly in an extraforaminal direction; however, pain reduction was satisfactory [12]. In contrast, Yun et al. found that 24 of 31 (77.4%) US-CRB procedures led to intraforaminal spreading after injection of 2 ml contrast medium [13]. Lee et al. reported that 1 ml contrast medium spread to the medial foramen and lateral foramen in 34% and 53% of cases, respectively [11]. They suggested that the spreading pattern of the contrast medium determined the degree of pain relief after US-CRB [11]. In a study by Park et al., 1 ml contrast agent was observed in the proximal spinal canal and the intraspinal epidural space in 29.7% of subjects who had US-CRB; however, treatment success was unrelated to the radiological findings [19]. The conflicting results obtained across previous studies may be explained by differences in the technical factors 1981

5 Kang et al. Figure 3 (A) and (C) Anteroposterior radiographic view showing 1 ml contrast agent delineating the nerve root. There is no visible spread into the epidural space. (B) and (D) Anteroposterior radiographic view indicates penetrated contrast medium in intraforaminal epidural space following 4 ml contrast medium injection (arrow). Table 2 solution Spreading pattern of contrast medium in relation to volume of injected Level of US-CRB a 1 ml Contrast Medium 4 ml Contrast Medium Extraforaminal Intraforaminal Extraforaminal Intraforaminal C5 level (N ¼ 1) C6 level (N ¼ 30) C7 level (N ¼ 22) a US-CRB ¼ ultrasound-guided cervical nerve root block. 1982

6 Volume Effect on Spreading in US-CRB Table 3 Comparison of clinical outcome according to spreading pattern Intraforaminal spreading (N ¼ 13) Extraforaminal spreading (N ¼ 40) Success rate (%) Pain relief (NRS a ) after 2 weeks (CI ) 92.5 (CI ) P value a NRS ¼ numeric rating scale (CI ) that might affect the spreading pattern of the injected solution in US-CRB, such as needle position and solution volume. In previous studies, the spreading patterns were assessed with injections of only 1 2 ml contrast medium. However, in US-CRB, the actual volume of medication injected is generally 3 5 ml. We had purposed to investigate whether volume could be a factor affecting a spreading pattern and to observe the actual spreading pattern of the injectant. We determined the spreading pattern of the solution in relation to the volume of injectant while controlling the needle position. To the best of our knowledge, this is the first study to investigate the volume effects of injectant in US-CRB. In this study, the injection of a small amount of contrast medium did not lead to the spreading of the injectant into the intraforaminal space, while the injection of a larger amount of solution did lead to intraforaminal spreading in 24.5% of patients. Therefore, the volume of injected solution could partially affect the spreading pattern. However, considering previous reports showing intraforaminal spreading with 1 2 ml contrast medium injection, the spreading patterns of injected solution in US-CRB procedure may also be affected by technical factors other than injectant volume, such as needle position. Some researchers have argued that, although the contrast medium spreads to the peripheral side, injected medications, such as corticosteroids and local anesthetics, spread to the central side [12,20]. According to Yamauchi et al., hydrostatic pressure and osmotic effect may cause the solutions to be absorbed into the nerve fibers, while the medications may spread toward the nerve root by intracellular fluid flow [12]. Jee et al. observed spreading of the contrast medium into the intraforaminal epidural space by comparing anteroposterior images taken after the contrast medium injections with washout images taken after drug injections in 25 patients [20]. They explained that, owing to differences in viscosity, injected drugs with a low viscosity may become diluted and spread the contrast medium to the central side [20]. In the present study, with regard to clinical outcome, the intraforaminal spread of the injectant did not relate to the efficacy of the procedure. Many studies have investigated the factors affecting the efficacy of US-CRB. According to Lee et al., the spread pattern of a contrast medium is the determinant of pain relief [11]. In contrast, Yamauchi et al. insisted that, despite the fact that injected solutions spread mainly in an extraforaminal direction, the pain relief effect was sufficient [12]. In some studies comparing the clinical efficacy between the US-CRB and fluoroscopy-guided C-TFSI, significant differences in outcome were not observed, regardless of spreading pattern [19,20]. There are several limitations in this study. The main limitation is the small sample size. Nonparametric tests were used in the statistical analysis due to the lack of a normal data distribution. In addition, only one patient had the procedure at the C5 level. Therefore, a larger sample study is required for a more accurate analysis. Second, the spreading pattern was assessed by only one examiner. Despite the fact that the examiner was blinded in the study, observer bias might have been present because no analysis for inter-observer agreement was conducted. Third, the clinical outcome assessments were limited. Since we had aimed to simply investigate the effect of injection volume on spreading pattern, the clinical outcomes were not evaluated precisely and serially. The pain scores were not assessed immediately after the procedure. The followup term was short, and serial follow-ups were not performed. In addition, functional outcome tools were not utilized. In subsequent studies, more precise and serial follow-ups of the clinical outcomes should be performed. Fourth, we analyzed the spreading patterns of the solution in relation to the volume of injectant at only one needle position. According to the study by Lee et al., the spreading pattern is influenced by the degree of contrast medium penetration [11]. It is possible that the degree of contrast medium penetration is affected by the delicate positioning of the needle around the nerve root. Fifth, the MRI findings were not considered as a factor influencing the spreading pattern. The degree of foraminal stenosis on MRI might also affect the intraforaminal spreading of the injectant. Finally, pain medications were not strictly controlled. Although additional pain medication was not allowed during the study, medications the patients had been taking before the study were not discontinued. Since the pain scores were assessed only in relation to radicular pain in the upper extremities, and because pain medications were not strictly controlled, the NRS scores may have been relatively low compared with other studies. The findings of the present study suggest that the volume of injected solution in US-CRB could affect the intraforaminal spread of injectant in some cases. However, the short-term outcome would not be affected by the spreading pattern because only a small proportion of injectant spread to the intraforaminal epidural 1983

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