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Selective blockade of the dorsal scapular nerve for scapula surgery
Journal of Clinical Anesthesia (2014) 26, 684–687
Case Report
Selective blockade of the dorsal scapular nerve for scapula surgery☆,☆☆,★ David B. Auyong MD (Staff Anesthesiologist)⁎, Amy A. Cabbabe MD (Fellow) Department of Anesthesiology, Virginia Mason Medical Center, Seattle, WA 98101, USA Received 2 August 2013; revised 2 June 2014; accepted 7 June 2014
Keywords: Dorsal scapular nerve; dorsal scapular nerve block; scapula surgery
Abstract The dorsal scapular nerve, a proximal branch of the brachial plexus, may be imaged using ultrasound. This nerve supplies the rhomboid and levator scapulae muscles while providing significant sensory innervation to the scapula. An ultrasound-guided nerve block of the dorsal scapular nerve provided analgesia after surgery of the scapula. Selective blockade of this nerve, without blocking the remainder of the brachial plexus, results in specific analgesia of the scapula, sparing sensory and motor function of the ipsilateral arm. © 2014 Elsevier Inc. All rights reserved.
1. Introduction The dorsal scapular nerve is a branch of the brachial plexus that diverges proximally from the root of C5 and occasionally from C6. Its origin from C5 most commonly occurs within the posterior cervical triangle, underneath the prevertebral fascia (Fig. 1). The dorsal scapular nerve supplies motor innervation to the rhomboid minor, rhomboid major, and levator scapulae. It pierces the middle scalene muscle and travels posterior to innervate the rhomboid major and minor muscles. Innervation to the levator scapulae muscle is more variable and may originate from the dorsal scapular nerve or the cervical plexus [1,2]. The rhomboid and levator scapulae muscles act together to retract and elevate the scapula [1–3]. ☆ Disclosures: Dr. Auyong has received honoraria from SonoSite, Bothell, WA, and Kimberly-Clark Corporation, Dallax, TX, USA, for educational lectures. No support from these companies has influenced this case report in any way. ☆☆ Supported by departmental funding only. ★ The patient has given signed consent for the publication of this case. ⁎ Correspondence: David Auyong, MD, Department of Anesthesiology, Virginia Mason Medical Center, 1100 Ninth Ave., MS: B2-AN, Seattle, WA 98101, USA. Tel.: +1 206 223 6980; fax: + 1 206 223 6982. E-mail address: [email protected] (D.B. Auyong).
http://dx.doi.org/10.1016/j.jclinane.2014.06.006 0952-8180/© 2014 Elsevier Inc. All rights reserved.
During embryologic development, scapula formation is more closely related to formation of the arm than formation of the axial skeleton. Osteotomes closely relate to the muscles overlying them. Therefore, sensory innervation of the scapula is supplied primarily supplied by the brachial plexus [4]. As the dorsal scapular nerve branches from the C5 or C6 nerve roots of the brachial plexus, it plays a significant role in sensory innervation of the scapula, along with the suprascapular and long thoracic nerves. Blocking these nerves prior to their exit from the brachial plexus provides analgesia for surgery of the scapula, but it also results in anesthesia of the ipsilateral arm, which may not be desired. The dorsal scapular and long thoracic nerve are readily identified with ultrasound at the interscalene level, separate from the remainder of the brachial plexus [5]. An ultrasound technique for selectively blocking the dorsal scapular nerve for scapular surgery is presented.
2. Case report A healthy 31 year old woman presented for scapular surgery for snapping scapula syndrome. The planned surgery was a bony transfer of the rhomboid muscles and the levator
Dorsal scapular nerve block scapulae (modified Eden-Lange muscle transfer). For postoperative analgesia, a single injection selective dorsal scapular nerve block was planned. The brachial plexus at the interscalene level between the anterior and middle scalene muscles was identified [6]. The probe was moved posterior to identify the dorsal scapular nerve lying within the body of the middle scalene muscle. The dorsal scapular nerve was identified as a monofascicular anechoic fascicle with a hyperechoic border (Fig. 2). Axial movement of the ultrasound probe confirmed the nerve and identified its emergence from the C5 nerve root (Fig. 3) [5]. A posterior inplane approach was used by advancing the needle towards the dorsal scapular nerve traversing the middle scalene muscle (Fig. 4). Ten mL of 0.5% bupivacaine was injected around the nerve using direct visualization for placement of the needle (21-gauge block needle). The patient underwent general anesthesia during the 3.5-hour case, then was brought to the recovery room awake with a pain score of 2 on an 11-point scale. The patient had full motor function of her ipsilateral arm in the postoperative period. She was transferred to the short-stay unit, but 14 hours after the initial nerve block she experienced significant intractable pain, rated at 10/10. At the patient’s request, a continuous nerve block catheter was placed adjacent to the dorsal scapular nerve. An infusion of 4 mL/hr + 2 mL bolus every 30 minutes was started. The patient experienced almost immediate relief of her pain after placement of the continuous
Fig. 1 Brachial plexus dissection illustrating the posterior course of the dorsal scapular nerve as it exits the plexus: 1) C5 nerve root, 2) middle scalene muscle, 3) dorsal scapular nerve, 4) transverse cervical artery (a branch from the thyrocervical trunk), 5) continuation of dorsal scapular nerve (joining with dorsal scapular artery - deep), 6) long thoracic nerve. 7) omohyoid muscle, and 8) anterior and posterior divisions of superior trunk.
685 nerve block. She was discharged home on postoperative day (POD) 1 after this block placement. Daily follow-up telephone calls disclosed that there was analgesia for the 4 days of continuous outpatient infusion without numbness or weakness of the ipsilateral upper extremity. The patient removed the catheter on POD 4 without complications.
3. Discussion Nerve blocks of the dorsal scapular nerve provide specific analgesia to the scapula, useful for both postoperative analgesia and in the diagnosis of chronic pain syndromes [7]. Pain originating from the scapula is difficult to diagnosis on physical examination [8], so this nerve block may have benefits beyond providing analgesia in acute postsurgical pain. As the embryologic origin of the scapula is very closely related to the formation of the upper extremity [4], it follows that the sensory innervation of the scapula arises primarily from the brachial plexus. Thus, anesthetizing the dorsal scapular nerve, a branch of the brachial plexus, provides analgesia for patients undergoing scapular surgery. In this case, this nerve was blocked with both a single-injection block and a continuous catheter, resulting in extended analgesia without anesthetizing the remainder of the brachial plexus. Anatomical variability does exist and in some patients the dorsal scapular nerve may not visible on ultrasound [5]. Blocking the entire brachial plexus may be an option for providing nonspecific analgesia to the scapula. With nerve stimulator approaches to the brachial plexus, localization of this nerve would result in stimulation of the rhomboid muscles, thereby signaling posterior needle placement [6]. Ultrasound guidance with an inplane technique and posterior approach requires the needle to traverse the middle scalene muscle, where the dorsal scapular nerve is often found. Needle approaches here risk dorsal scapular nerve injury, as this nerve diverges from the C5 nerve root [9]. Injury of the dorsal scapular nerve leads to scapular winging due to rhomboid dysfunction or posterior shoulder pain, as this nerve most likely contains not only motor but sensory fibers [2,10]. Injury to the long thoracic nerve recently was reported during an ultrasound-guided nerve block [11]. Injury to the dorsal scapular nerve has not yet been reported in the literature during regional anesthesia; however, complications of ultrasound-guided regional anesthesia persist [12,13]. Potential complications of nerve injury may be avoided by identifying the dorsal scapular nerve with ultrasound. Although the dorsal scapular nerve provides good analgesia to the osteotomes of the scapula, somatic innervation of the overlying skin is not covered with this selective block; thus additional analgesia may be required. Paravertebral or intercostal nerve blocks are good adjuncts to a selective dorsal scapular nerve block to target the somatic skin dermatomes for posterior scapular surgery (T2-T6).
686
D.B. Auyong, A.A. Cabbabe
Fig. 2 Dorsal scapular nerve image with brachial plexus. Left: anterior; right: posterior. AS = anterior scalene muscle, MS = middle scalene muscle, C5 = C5 nerve root – monofasicular, C6 = C6 nerve root - bifasicular. Large arrow = anechoic dorsal scapular nerve with hyperechoic epineurium.
Branches from the cervical plexus may capture the superior portion of the skin overlying the scapula [14]. Other branches of the brachial plexus may contribute to the osteotome innervation of the scapula, such as the suprascapular and long thoracic nerves; thus complete surgical anesthesia may not be possible with this approach alone. Other nerve blocks were discussed with the patient in this case. She received significant analgesic benefit with the selective dorsal scapular nerve block and therefore no additional nerve blocks were performed.
The dorsal scapular nerve may be associated with injury due to entrapment from middle scalene muscle hypertrophy, resulting in abnormal movement of the shoulder and winging of the scapula [3]. This syndrome is associated with shoulder or neck pain. Selective blockage of the dorsal scapular nerve may be more appropriate than a complete brachial plexus block to aid in the diagnosis of, and relief from, these types of specific pain syndromes [7,15]. In conclusion, surgery of the scapula is rare but it results in significant pain. This single case showed that clinical
Fig. 3 Emergence of dorsal scapular nerve from C5 nerve root. Left: anterior; right: posterior. This image is captured more cranial than Fig. 2. AS = anterior scalene muscle. MS = middle scalene muscle, C5 = C5 nerve root – monofasicular, C6 = C6 nerve root - monofasicular. Large arrow points to origin of dorsal scapular nerve from the C5 nerve root.
Dorsal scapular nerve block
687
Fig. 4 View of the 17-gauge (G) Tuohy needle inserted under the dorsal scapular nerve during catheter placement. C5 = C5 nerve root monofasicular. C6 = C6 nerve root - bifasicular. Hyperechoic epineurium of dorsal scapular nerve within middle scalene is visible shallow to the needle shaft. The 17-G needle is highlighted by arrows.
analgesia for scapular surgery is possible by selective blockage of the dorsal scapular nerve.
Acknowledgments We would like to thank Lucy S. Hostetter, MD, for assistance in preparation of this manuscript.
References [1] Frank DK, Wenk E, Stern JC, Gottlieb RD, Moscatello AL. A cadaveric study of the motor nerves to the levator scapulae muscle. Otolaryngol Head Neck Surg 1997;117:671-80. [2] Tubbs RS, Tyler-Kabara EC, Aikens AC, et al. Surgical anatomy of the dorsal scapular nerve. J Neurosurg 2005;102:910-1. [3] Akgun K, Aktas I, Terzi Y. Winged scapula caused by a dorsal scapular nerve lesion: a case report. Arch Phys Med Rehabil 2008;89:2017-20. [4] Cochard L. Netter's Atlas of Human Embryology. 1st ed. Teterboro (NJ): Icon Learning Systems LLC; 2002 185-8. [5] 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.
[6] Neal JM, Gerancher JC, Hebl JR, et al. Upper extremity regional anesthesia: essentials of our current understanding, 2008. Reg Anesth Pain Med 2009;34:134-70. [7] Haim K, Urban BJ. Dorsal scapular nerve block: description of technique and report of a case. Anesthesiology 1993;78:361-3. [8] Wright AA, Wassinger CA, Frank M, Michener LA, Hegedus EJ. Diagnostic accuracy of scapular physical examination tests for shoulder disorders: a systematic review. Br J Sports Med 2013;47: 886-92. [9] Marhofer P, Harrop-Griffiths W, Willschke H, Kirchmair L. Fifteen years of ultrasound guidance in regional anaesthesia: Part 2-recent developments in block techniques. Br J Anaesth 2010;104:673-83. [10] Debeer P, Van Den Eede E, Moens P. Scapular winging: an unusual complication of bracing in idiopathic scoliosis. Clin Orthop Relat Res 2007;461:258-61. [11] 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. [12] Cohen JM, Gray AT. Functional deficits after intraneural injection during interscalene block. Reg Anesth Pain Med 2010;35:397-9. [13] Reiss W, Kurapati S, Shariat A, Hadzic A. Nerve injury complicating ultrasound/electrostimulation-guided supraclavicular brachial plexus block. Reg Anesth Pain Med 2010;35:400-1. [14] Moore KL, Dalley AF, Agur AM. Clinically Oriented Anatomy. 6th ed. Philadelphia: Lippincott Williams & Wilkins; 2010 92-3 [693]. [15] Fisher MA, Gorelick PB. Entrapment neuropathies. Differential diagnosis and management. Postgrad Med 1985;77:160-74.
Case Report
Selective blockade of the dorsal scapular nerve for scapula surgery☆,☆☆,★ David B. Auyong MD (Staff Anesthesiologist)⁎, Amy A. Cabbabe MD (Fellow) Department of Anesthesiology, Virginia Mason Medical Center, Seattle, WA 98101, USA Received 2 August 2013; revised 2 June 2014; accepted 7 June 2014
Keywords: Dorsal scapular nerve; dorsal scapular nerve block; scapula surgery
Abstract The dorsal scapular nerve, a proximal branch of the brachial plexus, may be imaged using ultrasound. This nerve supplies the rhomboid and levator scapulae muscles while providing significant sensory innervation to the scapula. An ultrasound-guided nerve block of the dorsal scapular nerve provided analgesia after surgery of the scapula. Selective blockade of this nerve, without blocking the remainder of the brachial plexus, results in specific analgesia of the scapula, sparing sensory and motor function of the ipsilateral arm. © 2014 Elsevier Inc. All rights reserved.
1. Introduction The dorsal scapular nerve is a branch of the brachial plexus that diverges proximally from the root of C5 and occasionally from C6. Its origin from C5 most commonly occurs within the posterior cervical triangle, underneath the prevertebral fascia (Fig. 1). The dorsal scapular nerve supplies motor innervation to the rhomboid minor, rhomboid major, and levator scapulae. It pierces the middle scalene muscle and travels posterior to innervate the rhomboid major and minor muscles. Innervation to the levator scapulae muscle is more variable and may originate from the dorsal scapular nerve or the cervical plexus [1,2]. The rhomboid and levator scapulae muscles act together to retract and elevate the scapula [1–3]. ☆ Disclosures: Dr. Auyong has received honoraria from SonoSite, Bothell, WA, and Kimberly-Clark Corporation, Dallax, TX, USA, for educational lectures. No support from these companies has influenced this case report in any way. ☆☆ Supported by departmental funding only. ★ The patient has given signed consent for the publication of this case. ⁎ Correspondence: David Auyong, MD, Department of Anesthesiology, Virginia Mason Medical Center, 1100 Ninth Ave., MS: B2-AN, Seattle, WA 98101, USA. Tel.: +1 206 223 6980; fax: + 1 206 223 6982. E-mail address: [email protected] (D.B. Auyong).
http://dx.doi.org/10.1016/j.jclinane.2014.06.006 0952-8180/© 2014 Elsevier Inc. All rights reserved.
During embryologic development, scapula formation is more closely related to formation of the arm than formation of the axial skeleton. Osteotomes closely relate to the muscles overlying them. Therefore, sensory innervation of the scapula is supplied primarily supplied by the brachial plexus [4]. As the dorsal scapular nerve branches from the C5 or C6 nerve roots of the brachial plexus, it plays a significant role in sensory innervation of the scapula, along with the suprascapular and long thoracic nerves. Blocking these nerves prior to their exit from the brachial plexus provides analgesia for surgery of the scapula, but it also results in anesthesia of the ipsilateral arm, which may not be desired. The dorsal scapular and long thoracic nerve are readily identified with ultrasound at the interscalene level, separate from the remainder of the brachial plexus [5]. An ultrasound technique for selectively blocking the dorsal scapular nerve for scapular surgery is presented.
2. Case report A healthy 31 year old woman presented for scapular surgery for snapping scapula syndrome. The planned surgery was a bony transfer of the rhomboid muscles and the levator
Dorsal scapular nerve block scapulae (modified Eden-Lange muscle transfer). For postoperative analgesia, a single injection selective dorsal scapular nerve block was planned. The brachial plexus at the interscalene level between the anterior and middle scalene muscles was identified [6]. The probe was moved posterior to identify the dorsal scapular nerve lying within the body of the middle scalene muscle. The dorsal scapular nerve was identified as a monofascicular anechoic fascicle with a hyperechoic border (Fig. 2). Axial movement of the ultrasound probe confirmed the nerve and identified its emergence from the C5 nerve root (Fig. 3) [5]. A posterior inplane approach was used by advancing the needle towards the dorsal scapular nerve traversing the middle scalene muscle (Fig. 4). Ten mL of 0.5% bupivacaine was injected around the nerve using direct visualization for placement of the needle (21-gauge block needle). The patient underwent general anesthesia during the 3.5-hour case, then was brought to the recovery room awake with a pain score of 2 on an 11-point scale. The patient had full motor function of her ipsilateral arm in the postoperative period. She was transferred to the short-stay unit, but 14 hours after the initial nerve block she experienced significant intractable pain, rated at 10/10. At the patient’s request, a continuous nerve block catheter was placed adjacent to the dorsal scapular nerve. An infusion of 4 mL/hr + 2 mL bolus every 30 minutes was started. The patient experienced almost immediate relief of her pain after placement of the continuous
Fig. 1 Brachial plexus dissection illustrating the posterior course of the dorsal scapular nerve as it exits the plexus: 1) C5 nerve root, 2) middle scalene muscle, 3) dorsal scapular nerve, 4) transverse cervical artery (a branch from the thyrocervical trunk), 5) continuation of dorsal scapular nerve (joining with dorsal scapular artery - deep), 6) long thoracic nerve. 7) omohyoid muscle, and 8) anterior and posterior divisions of superior trunk.
685 nerve block. She was discharged home on postoperative day (POD) 1 after this block placement. Daily follow-up telephone calls disclosed that there was analgesia for the 4 days of continuous outpatient infusion without numbness or weakness of the ipsilateral upper extremity. The patient removed the catheter on POD 4 without complications.
3. Discussion Nerve blocks of the dorsal scapular nerve provide specific analgesia to the scapula, useful for both postoperative analgesia and in the diagnosis of chronic pain syndromes [7]. Pain originating from the scapula is difficult to diagnosis on physical examination [8], so this nerve block may have benefits beyond providing analgesia in acute postsurgical pain. As the embryologic origin of the scapula is very closely related to the formation of the upper extremity [4], it follows that the sensory innervation of the scapula arises primarily from the brachial plexus. Thus, anesthetizing the dorsal scapular nerve, a branch of the brachial plexus, provides analgesia for patients undergoing scapular surgery. In this case, this nerve was blocked with both a single-injection block and a continuous catheter, resulting in extended analgesia without anesthetizing the remainder of the brachial plexus. Anatomical variability does exist and in some patients the dorsal scapular nerve may not visible on ultrasound [5]. Blocking the entire brachial plexus may be an option for providing nonspecific analgesia to the scapula. With nerve stimulator approaches to the brachial plexus, localization of this nerve would result in stimulation of the rhomboid muscles, thereby signaling posterior needle placement [6]. Ultrasound guidance with an inplane technique and posterior approach requires the needle to traverse the middle scalene muscle, where the dorsal scapular nerve is often found. Needle approaches here risk dorsal scapular nerve injury, as this nerve diverges from the C5 nerve root [9]. Injury of the dorsal scapular nerve leads to scapular winging due to rhomboid dysfunction or posterior shoulder pain, as this nerve most likely contains not only motor but sensory fibers [2,10]. Injury to the long thoracic nerve recently was reported during an ultrasound-guided nerve block [11]. Injury to the dorsal scapular nerve has not yet been reported in the literature during regional anesthesia; however, complications of ultrasound-guided regional anesthesia persist [12,13]. Potential complications of nerve injury may be avoided by identifying the dorsal scapular nerve with ultrasound. Although the dorsal scapular nerve provides good analgesia to the osteotomes of the scapula, somatic innervation of the overlying skin is not covered with this selective block; thus additional analgesia may be required. Paravertebral or intercostal nerve blocks are good adjuncts to a selective dorsal scapular nerve block to target the somatic skin dermatomes for posterior scapular surgery (T2-T6).
686
D.B. Auyong, A.A. Cabbabe
Fig. 2 Dorsal scapular nerve image with brachial plexus. Left: anterior; right: posterior. AS = anterior scalene muscle, MS = middle scalene muscle, C5 = C5 nerve root – monofasicular, C6 = C6 nerve root - bifasicular. Large arrow = anechoic dorsal scapular nerve with hyperechoic epineurium.
Branches from the cervical plexus may capture the superior portion of the skin overlying the scapula [14]. Other branches of the brachial plexus may contribute to the osteotome innervation of the scapula, such as the suprascapular and long thoracic nerves; thus complete surgical anesthesia may not be possible with this approach alone. Other nerve blocks were discussed with the patient in this case. She received significant analgesic benefit with the selective dorsal scapular nerve block and therefore no additional nerve blocks were performed.
The dorsal scapular nerve may be associated with injury due to entrapment from middle scalene muscle hypertrophy, resulting in abnormal movement of the shoulder and winging of the scapula [3]. This syndrome is associated with shoulder or neck pain. Selective blockage of the dorsal scapular nerve may be more appropriate than a complete brachial plexus block to aid in the diagnosis of, and relief from, these types of specific pain syndromes [7,15]. In conclusion, surgery of the scapula is rare but it results in significant pain. This single case showed that clinical
Fig. 3 Emergence of dorsal scapular nerve from C5 nerve root. Left: anterior; right: posterior. This image is captured more cranial than Fig. 2. AS = anterior scalene muscle. MS = middle scalene muscle, C5 = C5 nerve root – monofasicular, C6 = C6 nerve root - monofasicular. Large arrow points to origin of dorsal scapular nerve from the C5 nerve root.
Dorsal scapular nerve block
687
Fig. 4 View of the 17-gauge (G) Tuohy needle inserted under the dorsal scapular nerve during catheter placement. C5 = C5 nerve root monofasicular. C6 = C6 nerve root - bifasicular. Hyperechoic epineurium of dorsal scapular nerve within middle scalene is visible shallow to the needle shaft. The 17-G needle is highlighted by arrows.
analgesia for scapular surgery is possible by selective blockage of the dorsal scapular nerve.
Acknowledgments We would like to thank Lucy S. Hostetter, MD, for assistance in preparation of this manuscript.
References [1] Frank DK, Wenk E, Stern JC, Gottlieb RD, Moscatello AL. A cadaveric study of the motor nerves to the levator scapulae muscle. Otolaryngol Head Neck Surg 1997;117:671-80. [2] Tubbs RS, Tyler-Kabara EC, Aikens AC, et al. Surgical anatomy of the dorsal scapular nerve. J Neurosurg 2005;102:910-1. [3] Akgun K, Aktas I, Terzi Y. Winged scapula caused by a dorsal scapular nerve lesion: a case report. Arch Phys Med Rehabil 2008;89:2017-20. [4] Cochard L. Netter's Atlas of Human Embryology. 1st ed. Teterboro (NJ): Icon Learning Systems LLC; 2002 185-8. [5] 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.
[6] Neal JM, Gerancher JC, Hebl JR, et al. Upper extremity regional anesthesia: essentials of our current understanding, 2008. Reg Anesth Pain Med 2009;34:134-70. [7] Haim K, Urban BJ. Dorsal scapular nerve block: description of technique and report of a case. Anesthesiology 1993;78:361-3. [8] Wright AA, Wassinger CA, Frank M, Michener LA, Hegedus EJ. Diagnostic accuracy of scapular physical examination tests for shoulder disorders: a systematic review. Br J Sports Med 2013;47: 886-92. [9] Marhofer P, Harrop-Griffiths W, Willschke H, Kirchmair L. Fifteen years of ultrasound guidance in regional anaesthesia: Part 2-recent developments in block techniques. Br J Anaesth 2010;104:673-83. [10] Debeer P, Van Den Eede E, Moens P. Scapular winging: an unusual complication of bracing in idiopathic scoliosis. Clin Orthop Relat Res 2007;461:258-61. [11] 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. [12] Cohen JM, Gray AT. Functional deficits after intraneural injection during interscalene block. Reg Anesth Pain Med 2010;35:397-9. [13] Reiss W, Kurapati S, Shariat A, Hadzic A. Nerve injury complicating ultrasound/electrostimulation-guided supraclavicular brachial plexus block. Reg Anesth Pain Med 2010;35:400-1. [14] Moore KL, Dalley AF, Agur AM. Clinically Oriented Anatomy. 6th ed. Philadelphia: Lippincott Williams & Wilkins; 2010 92-3 [693]. [15] Fisher MA, Gorelick PB. Entrapment neuropathies. Differential diagnosis and management. Postgrad Med 1985;77:160-74.