The conventional ultrasound-guided interscalene block targets the C5 and C6 nerve roots at approximately the level of the cricoid cartilage where they lie in the groove between the anterior and middle scalene muscles. This technique, although effective at providing regional anesthesia of the shoulder, is associated with risks of phrenic nerve palsy, injury to the dorsal scapular and long thoracic nerves, and long-term postoperative neurologic symptoms. In this case report, we describe the ultrasound-guided superior trunk block. This procedure targets the C5 and C6 components of the brachial plexus more distally after they unite into the superior trunk but before the suprascapular nerve branches off.
We performed an ultrasound-guided superior trunk block to provide perioperative analgesia for ambulatory arthroscopic shoulder repair in a patient with moderate chronic obstructive pulmonary disease. The technique, relevant sonoanatomy of the brachial plexus, and the potential advantages of the superior trunk block are discussed.
The enhanced anatomical knowledge provided by ultrasound-guidance has allowed anesthesiologists to devise new block techniques and refine existing ones. The superior trunk block is an example of this refinement and is intended as an alternative to the conventional interscalene block for anesthesia of the shoulder. Further research is planned to confirm the efficacy and safety of the technique.
Le bloc interscalénique échoguidé conventionnel cible les racines nerveuses C5 et C6 approximativement à la hauteur du cartilage cricoïde où elles traversent un espace entre les muscles scalènes antérieur et moyen. Bien que cette technique produise une anesthésie régionale efficace de l’épaule, elle est associée à des risques de paralysie du nerf phrénique, de lésion du nerf dorsal de la scapula et des nerfs thoraciques longs, ainsi qu’à des symptômes neurologiques postopératoires à long terme. Dans ce rapport de cas, nous décrivons un bloc échoguidé de la branche supérieure. Cette procédure cible les branches C5 et C6 du plexus brachial plus distalement, après leur union pour former la branche supérieure, mais avant la division du nerf suprascapulaire.
Nous avons pratiqué un bloc échoguidé de la branche supérieure pour obtenir une analgésie périopératoire au cours d’une réparation de l’épaule par voie arthroscopique en ambulatoire chez un patient ayant une maladie pulmonaire obstructive chronique d’intensité modérée. La technique, l’anatomie échographique pertinente du plexus brachial et les avantages du bloc de la branche supérieure sont discutés.
L’amélioration des connaissances anatomiques procurée par l’échoguidage a permis aux anesthésiologistes de mettre au point de nouvelles techniques de blocs et de raffiner celles qui existent. Le bloc de la branche supérieure est un exemple de ce raffinement et est vu comme une technique de remplacement du bloc interscalénique conventionnel pour l’anesthésie de l’épaule. D’autres études sont prévues pour confirmer l’efficacité et l’innocuité de la technique.
The interscalene block is a valuable analgesic option in shoulder surgery. It targets the C5 and C6 roots of the brachial plexus that give rise to the suprascapular nerve, axillary nerve, and lateral pectoral nerves that innervate the shoulder joint. The most common technique of ultrasound-guided interscalene block involves imaging the C5 and C6 roots at approximately the level of the cricoid cartilage, just distal to where they emerge from behind their respective transverse processes and where they lie in the groove between the anterior and middle scalene muscles (Fig. 1). The block needle is usually advanced in plane in a lateral-to-medial direction through the middle scalene muscle to contact the nerve roots and inject local anesthetic around them.1
Although this is a highly effective technique, it has some limitations, including a reported incidence of three cases per 1,000 of long-term (more than six months) postoperative neurologic symptoms (most commonly paresthesia or numbness; very rarely motor weakness)2 and an ever-present risk of phrenic nerve palsy despite injection of volumes as low as 5 mL.3,4 In this case report, we describe an alternative approach to C5/C6 blockade - the ultrasound-guided superior trunk block.
Written informed consent was obtained from the patient for inclusion in this report. A 55-yr-old male was scheduled for right arthroscopic shoulder surgery (Bankart repair with remplissage procedure) as an ambulatory surgery case. He was a heavy smoker with an 80-pack-year history and daily recreational use of marijuana, with resulting moderate chronic obstructive airways disease. Pulmonary function tests revealed post-bronchodilator values of FEV1/FVC 52% and FEV1% 62%. His medications included inhaled bronchodilator therapy (budesonide, formoterol, tiotropium bromide) and a statin for hypercholesterolemia. After discussing risks and benefits, the patient agreed to receive an ultrasound-guided superior trunk block for postoperative analgesia.
After applying standard monitoring,5 an ultrasound-guided superior trunk block was performed using a linear high-frequency (5-12 MHz) probe and a 22G 50-mm Stimuplex® block needle (B. Braun, Mississauga, ON, Canada). An injection of 0.25% bupivacaine 12 mL with epinephrine 0.0025 mg·mL−1 was administered, and an additional 5 mL of local anesthetic was injected superficial to the middle scalene muscle to block the supraclavicular nerves (lower branches of the superficial cervical plexus supplying the “cape” area of the shoulder).6 The patient exhibited motor and sensory blockade at 15 min without any subjective increase in work of breathing. Ultrasound of the ipsilateral diaphragm did not show paradoxical movement, further supporting an absence of clinically significant phrenic nerve paralysis.
The patient subsequently underwent a successful surgical repair under general anesthesia. His recovery was rapid and uneventful, and he was discharged four hours after emergence from anesthesia. At telephone follow-up the next day, the patient reported excellent postoperative analgesia with onset of pain evident approximately 23 hr after block completion. This was adequately controlled with oral analgesics. He had no respiratory or neurological symptoms.
Review of anatomy and sonoanatomy
The C5 and C6 roots are visible on ultrasound as dark hypoechoic circles emerging from their respective transverse process (Fig. 2A) and entering the groove between the anterior and middle scalene muscles (Fig. 2B and 2C). It is noteworthy that, in up to 30-35% of individuals, the C5 nerve root takes an anomalous course over or through the anterior scalene muscle rather than the interscalene groove (Fig. 3).7,8 Ultrasonographic identification of this anomaly is complicated by the fact that the C6 nerve root almost always splits into two hypoechoic bundles within the interscalene groove and can thus be mistaken for two separate roots (Fig. 2B and 2C; Fig. 3).8 It is vital to recognize this normal splitting of C6, as injection between these two structures would constitute an intraneural injection.
The C5 and C6 roots become increasingly superficial within the interscalene groove and eventually unite to form the superior trunk (Fig. 1), which is visible as a single complex structure with a hyperechoic connective tissue boundary lying just below the prevertebral (deep cervical) fascia (Fig. 2D). More distally in the root of the neck, the C8 and T1 roots unite to form the inferior trunk, while the C7 root forms the middle trunk.9 The trunks bifurcate into anterior and posterior divisions posterior to the clavicle,10 and these comprise the complex “bunch of grapes” appearance of the brachial plexus as it crosses the first rib in the ultrasonographic view that is used in the supraclavicular block.
Technical description of the superior trunk block
The C5 and C6 nerve roots are identified within the interscalene groove, but instead of targeting them at this level, they are traced distally to where they coalesce into the superior trunk. The block needle is advanced in plane in a lateral-to-medial direction under the deep cervical fascia and superficial to the middle scalene muscle until the tip is just adjacent to the lateral boundary of the superior trunk (Fig. 2D). An out-of-plane approach may also be used if preferred. Injection of local anesthetic at this point will hydrodissect the tissue plane around the superior trunk, and 10-15 mL will spread around it with minimal need for needle repositioning (see Video; available as Electronic Supplemental Material).
It is crucial to target the superior trunk proximal to the takeoff of the suprascapular nerve. This nerve is identified as a small hypoechoic circle that separates from the lateral aspect of the superior trunk (Figure 4) and courses laterally under the omohyoid muscle away from the brachial plexus.11 Therefore, if low volumes of local anesthetic are used, a more distal approach, such as the conventional ultrasound-guided supraclavicular plexus block, may miss the suprascapular nerve.
Ip and Tsui12 recently described a low interscalene approach that is similar to the superior trunk block in that the trunks, and not the roots, of the brachial plexus are targeted. Where their approach differs is that the low interscalene block is intended as an alternative to the supraclavicular plexus block for anesthesia of the upper limb distal to the shoulder. As a result, their site of needle insertion is slightly more distal. The needle is inserted through the middle scalene muscle to place the tip deeper, between the superior and middle trunks, and a larger volume of local anesthetic is injected.
In contrast, the superior trunk block is intended as an alternative to the conventional ultrasound-guided interscalene block for anesthesia of the shoulder and may offer several theoretical advantages.
First, the superior trunk has a clearly visible and well-defined connective tissue sheath which enhances resilience to needle-nerve contact. In contrast, the roots are surrounded by relatively little connective tissue and the epineurium is closely applied to the investing fascia of the interscalene groove, increasing the risk of sub-epineurial injection if visible needle-nerve contact is routinely sought.13 This may partly explain why registry data indicate that ultrasound-guided interscalene block continues to be associated with a higher risk of neurologic deficit compared with other blocks.2
Second, injury to the dorsal scapular and long thoracic nerves has recently been described in association with ultrasound-guided interscalene block.14,15 These nerves course through the middle scalene muscle at the level of the interscalene groove but are not always easy to visualize.16 The needle path in the superior trunk block does not traverse the middle scalene muscle and thus reduces the possibility of inadvertent needle trauma to these nerves.
Phrenic nerve palsy is a well-recognized risk of interscalene block but has received increased attention following recent reports of persistent phrenic nerve palsy, attributed in part to inflammatory scarring, perhaps from the myotoxicity of local anesthetics.17-19 The use of lower volumes of local anesthetic in ultrasound-guided interscalene block has been shown to reduce, but not eliminate, the incidence of phrenic nerve palsy.3,4 This is not surprising given that the phrenic nerve lies within 2 mm of the brachial plexus at the level of the cricoid cartilage (where it can often be seen superficial to the anterior scalene muscle).20 Nevertheless, it diverges from the brachial plexus by an additional 3mm for every 1cm that it descends into the root of the neck.20 It therefore seems prudent to inject local anesthetic as distal as possible in an attempt at further minimizing the risk of involvement of the phrenic nerve.
Finally, in the 30-35% of individuals whose C5 nerve root takes an anomalous course through the anterior scalene muscle,7,8 the scanning process associated with the superior trunk block facilitates recognition of this anatomic variation and improves the chance of block success, as the C5 root inevitably joins the C6 nerve root to form the superior trunk.
The main caveat to the superior trunk block is that the transverse cervical artery may lie across and superficial to the brachial plexus at this level.21 Its presence should always be excluded before commencing needle insertion by transiently releasing pressure on the probe (in case the vessel is compressed and therefore invisible) and use of colour Doppler.
One of the greatest advantages of ultrasound-guided regional anesthesia has been the enhanced knowledge of anatomy that it both demands as well as provides. It has also removed our dependence on surface anatomical landmarks, and these factors have allowed our specialty to devise new block techniques and refine existing ones. Further research is planned to confirm the efficacy and safety of the technique, in particular the incidence of phrenic nerve palsy, compared with the conventional ultrasound-guided interscalene block.
Nadeau MJ, Levesque S, Dion N. Ultrasound-guided regional anesthesia for upper limb surgery. Can J Anesth 2013; 60: 304-20.
Sites BD, Taenzer AH, Herrick MD, et al. Incidence of local anesthetic systemic toxicity and postoperative neurologic symptoms associated with 12,668 ultrasound-guided nerve blocks: an analysis from a prospective clinical registry. Reg Anesth Pain Med 2012; 37: 478-82.
Lee JH, Cho SH, Kim SH, et al. Ropivacaine for ultrasound-guided interscalene block: 5 mL provides similar analgesia but less phrenic nerve paralysis than 10 mL. Can J Anesth 2011; 58: 1001-6.
Riazi S, Carmichael N, Awad I, Holtby RM, McCartney CJ. Effect of local anaesthetic volume (20 vs 5 ml) on the efficacy and respiratory consequences of ultrasound-guided interscalene brachial plexus block. Br J Anaesth 2008; 101: 549-56.
Merchant R, Chartrand D, Dain S, et al. Guidelines to the practice of anesthesia – revised edition 2014. Can J Anesth 2014; 61: 46-71.
Maybin J, Townsley P, Bedforth N, Allan A. Ultrasound guided supraclavicular nerve blockade: first technical description and the relevance for shoulder surgery under regional anaesthesia. Anaesthesia 2011; 66: 1053-5.
Sakamoto Y. Spatial relationships between the morphologies and innervations of the scalene and anterior vertebral muscles. Ann Anat 2012; 194: 381-8.
Gutton C, Choquet O, Antonini F, Grossi P. Ultrasound-guided interscalene block: influence of anatomic variations in clinical practice (French). Ann Fr Anesth Reanim 2010; 29: 770-5.
Filip P. Complex arithmetic at the brachial plexus roots. Reg Anesth Pain Med 2009; 34: 79-80.
Mian A, Chaudhry I, Huang R, Risk E, Tubbs RS, Loukas M. Brachial plexus anesthesia: A review of the relevant anatomy, complications, and anatomical variations. Clin Anat 2014; 27: 210-21.
Siegenthaler A, Moriggl B, Mlekusch S, et al. Ultrasound-guided suprascapular nerve block, description of a novel supraclavicular approach. Reg Anesth Pain Med 2012; 37: 325-8.
Ip VH, Tsui BC. Lower interscalene approach for elbow surgery. Can J Anesth 20013; 60: 600-1.
Orebaugh SL, McFadden K, Skorupan H, Bigeleisen PE. Subepineurial injection in ultrasound-guided interscalene needle tip placement. Reg Anesth Pain Med 2010; 35: 450-4.
Saporito A. Dorsal scapular nerve injury: a complication of ultrasound-guided interscalene block. Br J Anaesth 2013; 111: 840-1.
Thomas SE, Winchester JB, Hickman G, DeBusk E. A confirmed case of injury to the long thoracic nerve following a posterior approach to an interscalene nerve block. Reg Anesth Pain Med 2013; 38: 370.
Hanson NA, Auyong DB. Systematic ultrasound identification of the dorsal scapular and long thoracic nerves during interscalene block. Reg Anesth Pain Med 2013; 38: 54-7.
Pakala SR, Beckman JD, Lyman S, Zayas VM. Cervical spine disease is a risk factor for persistent phrenic nerve paresis following interscalene nerve block. Reg Anesth Pain Med 2013; 38: 239-42.
Hogan QH. Phrenic nerve function after interscalene block revisited: now, the long view. Anesthesiology 2013; 119: 250-2.
Kaufman MR, Elkwood AI, Rose MI, et al. Surgical treatment of permanent diaphragm paralysis after interscalene nerve block for shoulder surgery. Anesthesiology 2013; 119: 484-7.
Kessler J, Schafhalter-Zoppoth I, Gray AT. An ultrasound study of the phrenic nerve in the posterior cervical triangle: implications for the interscalene brachial plexus block. Reg Anesth Pain Med 2008; 33: 545-50.
Murata H, Sakai A, Hadzic A, Sumikawa K. The presence of transverse cervical and dorsal scapular arteries at three ultrasound probe positions commonly used in supraclavicular brachial plexus blockade. Anesth Analg 2012; 115: 470-3.
Dr. Ki Jinn Chin is supported by a 2013-2015 Merit Award from the Department of Anesthesia, University of Toronto.
This work did not receive any direct funding support.
Conflicts of interest
David Burckett-St.Laurent and Ki Jinn Chin contributed substantially to the conception and drafting of the article. David Burckett-St.Laurent, Vincent Chan, and Ki Jinn Chin contributed substantially to the design and drafting of the article.
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Burckett-St.Laurent, D., Chan, V. & Chin, K.J. Refining the ultrasound-guided interscalene brachial plexus block: the superior trunk approach. Can J Anesth/J Can Anesth 61, 1098–1102 (2014). https://doi.org/10.1007/s12630-014-0237-3