SP34 Ultrasound guided spinal procedures – advantages and limitations

• Published in: Regional anesthesia and pain medicine Vol. 47; no. Suppl 1; pp. A37 - A40
• Main Author: Krol, Andrzej
• Format: Journal Article
• Language: English
• Published: BMJ Publishing Group Ltd 01.06.2022
• Subjects: Invited speakers
• ISSN: 1098-7339; 1532-8651
• DOI: 10.1136/rapm-2022-ESRA.39

In the last two decades high resolution ultrasound (HRU) revolutionised our approach to regional anaesthesia and interventional pain management. Author of this manuscript has witnessed and actively taken part in development, clinical assessment, and teaching of new ultrasound guided techniques.Ultrasound guided procedures have their strengths and weaknesses and in this narrative review author critically looks specifically at spinal procedures which were originally performed under fluoroscopy guidance.Introducing ultrasound to daily pain practice has unquestionable benefits: portability of device, cost effectiveness in regards of system purchase and maintaining, no need of an assistant/radiographer, and avoidance of radiation.The main questions to answer however are:1. Is it doable and easier under US guidance?2. Is it safer under US guidance?3. Is it more precise under US guidance?Abstract SP34 Table 1compares fluoroscopy and ultrasound for spinal interventions 1Cervical medial branch blockFluoroscopy guided cervical medial branch blocks has been well described and established however there is a large variability in clinical practice and the same end point might be reached with patient in prone, lateral or supine position depending on operator confidence and expertise. Recently consensus practice guidelines on interventions for cervical spine pain has been published in RAPM by international working group. 2 Ultrasound out of plane technique has been described by Siegenthaler, Eichenberger and Curatalo 3,4 in patient lateral position, with needle orientation from medial to lateral to minimize accidental vertebral artery puncture.Abstract SP34 Figure 1Demonstrates longitudinal scan in patient’s lateral position. Red circle depicts vertebral artery cranially. Yellow lines highlight facet joints, asterixis show MB position including TON on top of C2-C3 joint. Yellow arrows simulate needle direction out of planeScanning longitudinally from cranial to caudal starting with C2–3 facet joint which has characteristic appearance identified by the presence of a steep step at its upper border, indicating the lamina of C2 and third occipital nerve (TON) crossing over the joint. Following ‘hills’ (joints) and ‘valleys’ (waist of articular pillars with medial branches), from cranial to caudal one reaches superior articular process of C7 with C7 MB crossing over.It is simple and elegant technique suitable for diagnostic block but less so for radiofrequency denervation as needle/electrode is perpendicular to the course of the nerve. Newer electrodes such as ‘trident’ and ‘venom’ may allow for OOP approach in experience hands.Finlayson et al described in plane technique from posterior approach visualising the whole needle trajectory through posterior neck muscles and resting safe on the articular pillar5,6,7. One can assess structures cranial and caudal from the needle as well as in the front identifying posterior tubercle, nerve root and vessels prompting needle reposition. Precise electrode position close to articular pillar and along the medial branch could make it very safe technique, suitable for radiofrequency ablation with good outcome.There is a drawback of this technique requiring constant checking of the cervical level often requiring longitudinal scan as described previously.For safety, accuracy, precision and time efficiency at St George’s University Hospital Chronic Pain Service (author’s institution), combined fluoroscopy- ultrasound technique has been introduced and widely taught 7,8. Since 2012 we performed more than 500 CMB blocks and CMB RF.8,9 For patient in prone position, fluoroscopy helps to define the desired level and initial direction of the needle to achieve ‘tunnel vision’ and further progress to the upper middle part of articular pillar (Fig 2 a). Ultrasound helps to confirm the final needle position, parallel to the medial branch close to the articular pillar. Surrounding neurovascular structures such as the vertebral artery, radicular artery and the anterior nerve root can be identified before proceeding to perform a thermal lesion as illustrated in Figure 2 c. The needle position is verified in both longitudinal and transverse scanCervical RootsCervical peri radicular injections or selective nerve roots blocks (SNRB) have been well established in interventional pain practice. Sufficient evidence exists to support such an intervention in clinical situation of radicular pain as both diagnostic and therapeutic measures. One study demonstrated that more than 70% patients who responded to cervical nerve root block avoided surgical intervention.10 Cervical region with complex anatomyspinal cord and emerging neural structures, vertebral artery, radicular artery, spinal segmental artery, the ascending cervical artery, deep cervical artery has been potentially vulnerable. More than 100 neurological complications involving brain or spinal cord infarction have been reported. It has become an established practice to avoid particulate steroids at least in the cervical region as intraarterial injection of aforementioned may lead to fatality. Direct needle trauma could be another common cause of complications and in author’s humble opinion fluoroscopy guided intervention lacks the safety with no appreciation of the surrounding structures chiefly nerves and vessels. Ultrasound is not an ultimate solution, and it may lead to image misinterpretation and wrong needle position but potentially makes it less likely.Figures 3 and 4 demonstrate both ultrasound and fluoroscopy imaging for the most performed C6 and C7 nerve root both following characteristic pattern of recognition.The other safety measure advocated by the author of this review is applying injection pressure monitoring to avoid pressure higher than 15 psi as a detection of intraneural needle positioning. Too vigorous injection may also increase injection pressure resulting in untoward spread.11 Finally, motor response at low current 0.2–0.3 mA indicates needle- nerve contact and should be avoided. 12 Abstract SP34 Figure 2Ultrasound and fluoroscopy combined for cervical medial branch radiofrequency denervation. a) Lateral and A-P view of fluoroscopy images in patient in prone position. Note needle ‘tunnel vision’ in A-P position. Lateral view showsneedle position at the level of articular pillar from single entry point. b) Ultrasound probe position in longitudinal and transverse neck scans to assess needle position. c) Ultrasound images in transverse scan. Needle alongside and close to the articular pillar, parallel to the medial branchAbstract SP34 Figure 3From top left – Ultrasound image in transverse view showing from left to right: Th-Thyroid gland, SCM- Sternocleidomastoid Muscle, LC-Longus Coli muscle, AT-anterior tubercle of C6 transverse process, C6 – C6 nerve root transverse and longitudinal view. From bottom left – Ultrasound probe on skeleton model, AP and Lateral fluoroscopy projection with contrastAbstract SP34 Figure 4From top left -Ultrasound images showing C7 nerve root in transverse view including colour doppler and depiction in red. Note vertebral artery in front of the C7 nerve root and lack of anterior tubercle. From bottom left - Ultrasound probe on skeleton model, AP, and Lateral fluoroscopy projection with contrastAbstract SP34 Figure 5A)Patient in lateral position for extraforaminal cervical nerve root block. B) Cadaver dissection demonstrating cervical roots C5, C6, C7 root stained with dye after injection of 1 ml methylene blue. C) Lateral fluoroscopy with needle. D) AP fluoroscopy view with needle through foramen within spinal cord. ( simulated on cadaver)The discussion may spark about terminology of transforaminal and extraforaminal needle position. Intra foraminal nerve course varies between 6–8mm. Ultrasound guided injection are extraforaminal as needle does not advance beyond the point where it cannot be seen. This is paramount for safety of ultrasound guided interventions. To author’s knowledge there is no data comparing the clinical outcome of both techniques.From author’s own data there is more than sufficient dye spread along nerve root with extraforaminal injection and further needle advancement into tight foramen may bring the risk of vascular or neural damage including spinal cord injury as presented in figure 5Thoracic SpineThoracic spine and surrounding structures are amenable for US guided interventions, the most advanced being thoracic nerve root, epidural injections, paravertebral block. The least erector spinae plane block with its various descriptions and outcomes. Ventral ramus (intercostal nerves) and dorsal ramus giving off medial and lateral branch are frequent targets along with costotransverse ligaments being common pain triggers.Chronic pain interventions are often diagnostic, searching for the source of pain and ultrasound helps to identify anatomical topography.Abstract SP34 Figure 6Thoracic spine with ventral and dorsal rami and probe position with obtained sono images. From the top: at the level of costo-transverse joint,Abstract SP34 Figure 7From left to right. Paravertebral spread of contrast dye. Skeleton of thoracic spine. Thoracic spine with ventral and dorsal rami, contrast dye along thoracic nerveIn the middle: transverse probe position at the level of paravertebral space limited posteriorly by superior transverse ligament. At the bottom sagittal paramedian probe position at the level of paravertebral space. The latest often leads to too lateral probe position and in fact intercostal nerve blockFollowing the golden rule of not advancing the needle beyond the point of visibility, the combination with fluoroscopy and assessment of contrast spread seems like a good practice.One will find difficult to identify exact thoracic level with ultrasound only - fluoroscopy can be of a great help hereLumbar SpinePain procedures at the lumbar level has been traditionally performed under fluoroscopy guidance.