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Variant location of the musculocutaneous nerve during axillary nerve block
Journal of Clinical Anesthesia (2006) 18, 541 – 544
Case report
Variant location of the musculocutaneous nerve during axillary nerve block Steven L. Orebaugh MD (Assistant Professor)a,b,*, Scott Pennington DO (CA-3 Resident)b a
Department of Anesthesiology, University of Pittsburgh Medical Center-Southside, Pittsburgh, PA 15203, USA Division of Anesthesia, Naval Medical Center, Portsmouth, VA, USA
b
Received 30 October 2005; revised 18 March 2006; accepted 26 March 2006
Keywords: Musculocutaneous nerve; Anatomy; Variation; Axillary block
Abstract We present the case of a 56-year-old man who underwent axillary nerve block for a wrist arthroscopy procedure, with real-time ultrasound and peripheral nerve stimulator guidance. The ulnar nerve and radial nerve were located medial and posterior to the brachial artery, respectively. A large complex structure was noted in the position typically occupied by the median nerve. Contact of this structure with the stimulating needle produced strong biceps contraction, and slight adjustment of the needle resulted in forearm pronation. After injection of 10 mL of local anesthetic near this structure, it appeared to consist of two separate components on ultrasound. We believe that these components represented the median and musculocutaneous nerves lying together, lateral to the artery. Radial, median, ulnar, and musculocutaneous nerve block ensued, and wrist arthroscopy was carried out uneventfully. Knowledge of this anatomical variation may improve anesthesiologists’ ability to provide effective axillary block. D 2006 Elsevier Inc. All rights reserved.
1. Introduction Understanding peripheral nerve anatomy is essential for effective nerve block. Variation from standard anatomic organization is not uncommon. In this case, real-time ultrasound needle guidance helped illustrate a case of the musculocutaneous nerve running with the median nerve, giving rise to an unusual nerve stimulation pattern.
2. Case report A 56-year-old man presented for left wrist arthroscopy to evaluate chronic pain. After consent was obtained to * Corresponding author. UPMC-Southside Anesthesia, Pittsburgh, PA 15203, USA. Tel.: +1 412 488 5799; fax: +1 412 488 5796. E-mail address: [email protected] (S.L. Orebaugh). 0952-8180/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jclinane.2006.03.010
administer regional anesthesia, monitors were placed and the patient received 1 mg of midazolam and 50 lg of fentanyl for sedation. He remained alert and responsive throughout the block. The axillary approach to brachial plexus block was elected, and it was carried out with realtime ultrasound guidance (5-10 MHz transducer; SonoSite Titan, Bothell, WA) in concert with peripheral nerve stimulation. The nerve stimulator was set at 0.4 mA and 2-Hz stimulating frequency. Medial and posterior to the brachial artery, the ulnar and radial nerves, respectively, were located and stimulated with the 50-mm 22-gauge needle tip (Stimuplex; B Braun, Melsungen, Germany) with ultrasound guidance, confirming their identities. Fifteen milliliters of an equal mixture of 0.5% ropivacaine and 1.5% mepivacaine was injected around the radial nerve and 10 mL around the ulnar nerve. The neurovascular bundle was then approached from the lateral side, and the needle was
542
Fig. 1 Transverse ultrasonographic image of axillary region. The stimulating needle is shown contacting the large complex structure initially believed to be the median nerve.
directed toward a comparatively large complex structure thought to be the median nerve (Fig. 1). As the needle contacted this structure, strong biceps flexion was noted, in concert with pronation of the forearm. With slight adjustment of the needle tip, turning the bevel, the biceps flexion weakened, and pronation became more prominent, with palpable muscle contraction in the proximal forearm. Local anesthetic solution of 10 mL was then injected and was noted to spread about the structures noted. Given this unusual pattern of peripheral nerve stimulation, we believe that the musculocutaneous and median nerves were fused into one structure or were running together along the lateral aspect of the brachial artery, at the axillary level (Fig. 2). Scanning the coracobrachialis muscle,
S.L. Orebaugh, S. Pennington
Fig. 3 Transverse sonographic image of high humeral region, with transducer position distal to that seen in Fig. 1. Here, the musculocutaneous nerve (MC) appears to proceed laterally, because it courses to innervate the elbow flexors. M = median nerve; A = brachial artery.
lateral and superior to the artery and the sheath (which were at this time well-delineated by the bolus of injected local anesthetic), revealed no apparent neural structures that could represent the musculocutaneous nerve. The apparent median nerve was traced distally with the ultrasound probe and appeared to release a large branch laterally, approximately 5 cm below the axillary level (Fig. 3). Ultrasonography was used to confirm that a local anesthetic bhaloQ surrounded each of the three nerves of interest. The two structures considered to be the musculocutaneous and median nerves remained together after injection of local anesthetic, although they became separated from the artery (Fig. 2). Over the next 30 minutes, the radial, ulnar, and musculocutaneous nerves were completely anesthetized, whereas the median nerve was slower to achieve full block. By 45 minutes, the block was complete. Arthroscopy was carried out with two portals on the distal aspect of the wrist, with complete surgical anesthesia. The nerve territories affected by the surgical procedure included those of the radial, ulnar, and musculocutaneous nerves. No further sedation was necessary during surgery.
3. Discussion
Fig. 2 Transverse sonographic image of axillary region. After injection of local anesthetic solution, the large irregular structure thought to be the median nerve appears to consist of two separate structures, most likely the musculocutaneous nerve (MC) and median nerve (M) lying together, according to the nerve stimulation patterns. A = brachial artery; CB = coracobrachialis muscle.
Axillary nerve block may be carried out by paresthesia technique, transarterial technique, peripheral nerve stimulation, or real-time ultrasound guidance. No clear benefit has been established incontrovertibly for any one of these techniques, but it appears that specifically blocking the terminal nerves improves success [1]. Ultrasonography at the axillary level delineates the terminal nerves of the brachial plexus, the brachial artery, and one or more veins. The nerves at this level appear to be round or oval hypoechoic structures, with punctuated
Variant musculocutaneous nerve location internal echoes [2]. The radial, ulnar, and median nerve are usually well visualized by ultrasound within the neurovascular bundle, though their positions next to the artery can be quite variable and may change with even light pressure placed on them [3]. The musculocutaneous nerve, unlike the other terminal nerves of the upper extremity, lies outside the neurovascular bundle and fascial confines at this level in most patients [4]. It is typically visualized in the substance of the coracobrachialis muscle [5]. Anatomical variants from expected patterns of peripheral nerve location can create challenges for the regional anesthesiologist. In the arm, variations of the nerves innervating the ventral compartment (musculocutaneous, median, and ulnar nerves) are much more common than those of the dorsal compartment (radial) [4]. The most commonly noted aberration of peripheral nerve organization in the upper extremity is communication of the musculocutaneous with the median nerve, occurring in up to 20% of patients [6]. In 138 cadaver specimens, Choi et al [7] described variations in connections between the musculocutaneous and median nerves in 26% of the dissected arms. They organized these variations into three classifications: complete fusion of both nerves (19% of variants), one supplementary branch between the two nerves (72%), or two supplementary branches between them (7%). Venieratos and Anagnostopoulou [8] investigated 79 cadaver specimens and reported variable communications between the musculocutaneous and median nerves in 16 specimens (20%), with 6 being bilateral. In a study of 30 cadavers, Beheiry [9] also described the nature of the musculocutaneous-median nerve communication, finding them in 8.4% of the arms dissected. Schafhalter-Zoppoth and Gray [10] characterized the appearance of the musculocutaneous nerve on ultrasound. They noted that if this nerve was not visible in the coracobrachialis muscle, it was likely fused with the median nerve, later to separate from it. In a dissection of 129 cadavers, Loukas and Aqueelah [11] described 4 different types of communication between the musculocutaneous and median nerves: those that occur proximal to the musculocutaneous nerve entry into coracobrachialis, those that occur distal to entry into this muscle, those in which there is no entry of the musculocutaneous nerve into the coracobrachialis at all, and those with multiple connections both proximal and distal to the entry of the musculocutaneous nerve into the coracobrachialis muscle. In a study of 54 dissected cadaver arms, Eglseder and Goldman [12] reported a 36% incidence of interconnections between the median and musculocutaneous nerves. Another variation is complete absence of the musculocutaneous nerve. This variation is less common than the patterns described above. One of the specimens in Beheiry’s series was noted to have complete fusion of the median and musculocutaneous nerves, with branches to the coracobrachialis, biceps brachii, and brachialis, and with a distinct distal branch continuing as the lateral cutaneous nerve of the
543 forearm [9]. Rao and Chaudhary [13] similarly identified this phenomenon in two of 24 cadavers dissected. In these cases, the innervation of arm flexors occurred via direct branches from the median nerve. The dimensions of the presumed median and musculocutaneous nerves are comparable with the published measurements from ultrasound studies of peripheral nerves. The dimensions of the nerve presumed to be the median nerve (Fig. 2) are 4.2 mm in width and 2.4 mm in anteroposterior diameter. Heinemeyer and Reimers [14] reported a transverse diameter of the median nerve at mid– forearm levels of 2.9 to 4.1 mm and an anteroposterior diameter of 2.9 to 3.5 mm. Gray et al reported that the musculocutaneous nerve dimensions at its entrance into the coracobrachialis muscle were 3.5 F 1.0 mm in transverse diameter and 1.9 F 0.6 mm in anteroposterior diameter [10], whereas the measurements of the structure presumed to be the musculocutaneous nerve in this report were 3.0 and 2.5 mm, respectively (Fig. 2). In the case reported herein, the brisk strong biceps contraction in response to stimulation of the enlarged complex median nerve in the axillary neurovascular bundle (Fig. 2) suggested one of two possibilities. Either the musculocutaneous nerve was adjoined to the median nerve, only to separate from it more distally, or it was completely fused to the median nerve. When this large structure was followed with the transducer distally in the arm, it appeared to bifurcate or to release a large branch in the lateral direction (Fig. 3). This finding suggested that the musculocutaneous nerve was running together with the median nerve in the axilla and then became separated from it at the midhumeral level. The inability to identify the musculocutaneous nerve in the coracobrachialis muscle with ultrasonography and the complete block of both the median and musculocutaneous nerves after injection of local anesthetic around this one structure appeared to confirm this variant anatomy. Anesthesia occurred more slowly in the median nerve. Because the musculocutaneous and median nerves appear to have been fused at this level, fascicles of the former may have been closest to the site of local anesthetic injection. Another explanation is that connective tissue separating the two structures may have limited the diffusion of local anesthetic solution to the median nerve. Appreciation of variations in anatomy is an important regional anesthesia. Failure to understand that the musculocutaneous nerve may run with the median nerve may lead to physician frustration and patient discomfort or injury. In this case, real-time sonographic guidance of axillary block was of benefit in understanding this common anatomical variation and sparing the patient repeated attempts at blocking of the musculocutaneous nerve within the coracobrachialis muscle. If the axillary block had been performed with either nerve stimulation or by transarterial technique, the unusual pattern might not have been appreciated, because injection of local anesthetic within the confines of
544 the neurovascular bundle likely would have produced a successful block.
References [1] Neal JM, Hebl JR, Gerancher JC, et al. Brachial plexus anesthesia: essentials of our current understanding. Reg Anesth Pain Med 2002; 27:402 - 28. [2] Perlas A, Chan VW, Simons M. Brachial plexus examination and localization using ultrasound and electrical stimulation. Anesthesiology 2003;99:429 - 35. [3] Retzl G, Kapral S, Greher M, et al. Ultrasonographic findings of the axillary part of the brachial plexus. Anesth Analg 2001;92:1271 - 5. [4] Delaunay L, Jochum D. Anatomy of the brachial plexus. In: Chelly JE, editor. Peripheral nerve blocks: a color atlas, 2nd ed Philadelphia7 Lippincott Williams and Wilkins; 2004. p. 28 - 38. [5] Spence BC, Sites BD, Beach ML. Ultrasound-guided musculocutaneous nerve block: a description of a novel technique. Reg Anesth Pain Med 2005;30:198 - 201. [6] Bergmann RA, Thompson SA, Afifi AK. Compendium of human anatomic variation. Baltimore7 Urban and Schwarzenberg; 1988.
S.L. Orebaugh, S. Pennington [7] Choi D, Rodriguez-Niedenfuhr M, Vazquez T, et al. Patterns of connections between the musculocutaneous and median nerves in the axilla and arm. Clin Anat 2002;15:11 - 7. [8] Venieratos D, Anagnostopoulou S. Classification of communications between the musculocutaneous and median nerves. Clin Anat 1998; 11:327 - 31. [9] Beheiry EE. Anatomical variations of the median nerve distribution and communication in the arm. Folia Morphol 2004;63: 313 - 8. [10] Schafhalter-Zoppoth I, Gray AT. The musculocutaneous nerve: ultrasound appearance for peripheral nerve block. Reg Anesth Pain Med 2005;30:385 - 90. [11] Loukas M, Aqueelah H. Musculocutaneous and median nerve connections within, proximal and distal to the coracobrachialis muscle. Folia Morphol 2005;64:101 - 8. [12] Eglseder WA Jr, Goldman M. Anatomic variations of the musculocutaneous nerve in the arm. Am J Orthop 1997;26:777 - 80. [13] Rao PV, Chaudhary SC. Absence of musculocutaneous nerve: two case reports. Clin Anat 2001;14:31 - 5. [14] Heinemeyer O, Reimers CD. Ultrasound of radial, ulnar, median and sciatic nerves in healthy subjects and patients with hereditary motor and sensory neuropathies. Ultrasound Med Biol 1999;25: 481 - 5.
Case report
Variant location of the musculocutaneous nerve during axillary nerve block Steven L. Orebaugh MD (Assistant Professor)a,b,*, Scott Pennington DO (CA-3 Resident)b a
Department of Anesthesiology, University of Pittsburgh Medical Center-Southside, Pittsburgh, PA 15203, USA Division of Anesthesia, Naval Medical Center, Portsmouth, VA, USA
b
Received 30 October 2005; revised 18 March 2006; accepted 26 March 2006
Keywords: Musculocutaneous nerve; Anatomy; Variation; Axillary block
Abstract We present the case of a 56-year-old man who underwent axillary nerve block for a wrist arthroscopy procedure, with real-time ultrasound and peripheral nerve stimulator guidance. The ulnar nerve and radial nerve were located medial and posterior to the brachial artery, respectively. A large complex structure was noted in the position typically occupied by the median nerve. Contact of this structure with the stimulating needle produced strong biceps contraction, and slight adjustment of the needle resulted in forearm pronation. After injection of 10 mL of local anesthetic near this structure, it appeared to consist of two separate components on ultrasound. We believe that these components represented the median and musculocutaneous nerves lying together, lateral to the artery. Radial, median, ulnar, and musculocutaneous nerve block ensued, and wrist arthroscopy was carried out uneventfully. Knowledge of this anatomical variation may improve anesthesiologists’ ability to provide effective axillary block. D 2006 Elsevier Inc. All rights reserved.
1. Introduction Understanding peripheral nerve anatomy is essential for effective nerve block. Variation from standard anatomic organization is not uncommon. In this case, real-time ultrasound needle guidance helped illustrate a case of the musculocutaneous nerve running with the median nerve, giving rise to an unusual nerve stimulation pattern.
2. Case report A 56-year-old man presented for left wrist arthroscopy to evaluate chronic pain. After consent was obtained to * Corresponding author. UPMC-Southside Anesthesia, Pittsburgh, PA 15203, USA. Tel.: +1 412 488 5799; fax: +1 412 488 5796. E-mail address: [email protected] (S.L. Orebaugh). 0952-8180/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jclinane.2006.03.010
administer regional anesthesia, monitors were placed and the patient received 1 mg of midazolam and 50 lg of fentanyl for sedation. He remained alert and responsive throughout the block. The axillary approach to brachial plexus block was elected, and it was carried out with realtime ultrasound guidance (5-10 MHz transducer; SonoSite Titan, Bothell, WA) in concert with peripheral nerve stimulation. The nerve stimulator was set at 0.4 mA and 2-Hz stimulating frequency. Medial and posterior to the brachial artery, the ulnar and radial nerves, respectively, were located and stimulated with the 50-mm 22-gauge needle tip (Stimuplex; B Braun, Melsungen, Germany) with ultrasound guidance, confirming their identities. Fifteen milliliters of an equal mixture of 0.5% ropivacaine and 1.5% mepivacaine was injected around the radial nerve and 10 mL around the ulnar nerve. The neurovascular bundle was then approached from the lateral side, and the needle was
542
Fig. 1 Transverse ultrasonographic image of axillary region. The stimulating needle is shown contacting the large complex structure initially believed to be the median nerve.
directed toward a comparatively large complex structure thought to be the median nerve (Fig. 1). As the needle contacted this structure, strong biceps flexion was noted, in concert with pronation of the forearm. With slight adjustment of the needle tip, turning the bevel, the biceps flexion weakened, and pronation became more prominent, with palpable muscle contraction in the proximal forearm. Local anesthetic solution of 10 mL was then injected and was noted to spread about the structures noted. Given this unusual pattern of peripheral nerve stimulation, we believe that the musculocutaneous and median nerves were fused into one structure or were running together along the lateral aspect of the brachial artery, at the axillary level (Fig. 2). Scanning the coracobrachialis muscle,
S.L. Orebaugh, S. Pennington
Fig. 3 Transverse sonographic image of high humeral region, with transducer position distal to that seen in Fig. 1. Here, the musculocutaneous nerve (MC) appears to proceed laterally, because it courses to innervate the elbow flexors. M = median nerve; A = brachial artery.
lateral and superior to the artery and the sheath (which were at this time well-delineated by the bolus of injected local anesthetic), revealed no apparent neural structures that could represent the musculocutaneous nerve. The apparent median nerve was traced distally with the ultrasound probe and appeared to release a large branch laterally, approximately 5 cm below the axillary level (Fig. 3). Ultrasonography was used to confirm that a local anesthetic bhaloQ surrounded each of the three nerves of interest. The two structures considered to be the musculocutaneous and median nerves remained together after injection of local anesthetic, although they became separated from the artery (Fig. 2). Over the next 30 minutes, the radial, ulnar, and musculocutaneous nerves were completely anesthetized, whereas the median nerve was slower to achieve full block. By 45 minutes, the block was complete. Arthroscopy was carried out with two portals on the distal aspect of the wrist, with complete surgical anesthesia. The nerve territories affected by the surgical procedure included those of the radial, ulnar, and musculocutaneous nerves. No further sedation was necessary during surgery.
3. Discussion
Fig. 2 Transverse sonographic image of axillary region. After injection of local anesthetic solution, the large irregular structure thought to be the median nerve appears to consist of two separate structures, most likely the musculocutaneous nerve (MC) and median nerve (M) lying together, according to the nerve stimulation patterns. A = brachial artery; CB = coracobrachialis muscle.
Axillary nerve block may be carried out by paresthesia technique, transarterial technique, peripheral nerve stimulation, or real-time ultrasound guidance. No clear benefit has been established incontrovertibly for any one of these techniques, but it appears that specifically blocking the terminal nerves improves success [1]. Ultrasonography at the axillary level delineates the terminal nerves of the brachial plexus, the brachial artery, and one or more veins. The nerves at this level appear to be round or oval hypoechoic structures, with punctuated
Variant musculocutaneous nerve location internal echoes [2]. The radial, ulnar, and median nerve are usually well visualized by ultrasound within the neurovascular bundle, though their positions next to the artery can be quite variable and may change with even light pressure placed on them [3]. The musculocutaneous nerve, unlike the other terminal nerves of the upper extremity, lies outside the neurovascular bundle and fascial confines at this level in most patients [4]. It is typically visualized in the substance of the coracobrachialis muscle [5]. Anatomical variants from expected patterns of peripheral nerve location can create challenges for the regional anesthesiologist. In the arm, variations of the nerves innervating the ventral compartment (musculocutaneous, median, and ulnar nerves) are much more common than those of the dorsal compartment (radial) [4]. The most commonly noted aberration of peripheral nerve organization in the upper extremity is communication of the musculocutaneous with the median nerve, occurring in up to 20% of patients [6]. In 138 cadaver specimens, Choi et al [7] described variations in connections between the musculocutaneous and median nerves in 26% of the dissected arms. They organized these variations into three classifications: complete fusion of both nerves (19% of variants), one supplementary branch between the two nerves (72%), or two supplementary branches between them (7%). Venieratos and Anagnostopoulou [8] investigated 79 cadaver specimens and reported variable communications between the musculocutaneous and median nerves in 16 specimens (20%), with 6 being bilateral. In a study of 30 cadavers, Beheiry [9] also described the nature of the musculocutaneous-median nerve communication, finding them in 8.4% of the arms dissected. Schafhalter-Zoppoth and Gray [10] characterized the appearance of the musculocutaneous nerve on ultrasound. They noted that if this nerve was not visible in the coracobrachialis muscle, it was likely fused with the median nerve, later to separate from it. In a dissection of 129 cadavers, Loukas and Aqueelah [11] described 4 different types of communication between the musculocutaneous and median nerves: those that occur proximal to the musculocutaneous nerve entry into coracobrachialis, those that occur distal to entry into this muscle, those in which there is no entry of the musculocutaneous nerve into the coracobrachialis at all, and those with multiple connections both proximal and distal to the entry of the musculocutaneous nerve into the coracobrachialis muscle. In a study of 54 dissected cadaver arms, Eglseder and Goldman [12] reported a 36% incidence of interconnections between the median and musculocutaneous nerves. Another variation is complete absence of the musculocutaneous nerve. This variation is less common than the patterns described above. One of the specimens in Beheiry’s series was noted to have complete fusion of the median and musculocutaneous nerves, with branches to the coracobrachialis, biceps brachii, and brachialis, and with a distinct distal branch continuing as the lateral cutaneous nerve of the
543 forearm [9]. Rao and Chaudhary [13] similarly identified this phenomenon in two of 24 cadavers dissected. In these cases, the innervation of arm flexors occurred via direct branches from the median nerve. The dimensions of the presumed median and musculocutaneous nerves are comparable with the published measurements from ultrasound studies of peripheral nerves. The dimensions of the nerve presumed to be the median nerve (Fig. 2) are 4.2 mm in width and 2.4 mm in anteroposterior diameter. Heinemeyer and Reimers [14] reported a transverse diameter of the median nerve at mid– forearm levels of 2.9 to 4.1 mm and an anteroposterior diameter of 2.9 to 3.5 mm. Gray et al reported that the musculocutaneous nerve dimensions at its entrance into the coracobrachialis muscle were 3.5 F 1.0 mm in transverse diameter and 1.9 F 0.6 mm in anteroposterior diameter [10], whereas the measurements of the structure presumed to be the musculocutaneous nerve in this report were 3.0 and 2.5 mm, respectively (Fig. 2). In the case reported herein, the brisk strong biceps contraction in response to stimulation of the enlarged complex median nerve in the axillary neurovascular bundle (Fig. 2) suggested one of two possibilities. Either the musculocutaneous nerve was adjoined to the median nerve, only to separate from it more distally, or it was completely fused to the median nerve. When this large structure was followed with the transducer distally in the arm, it appeared to bifurcate or to release a large branch in the lateral direction (Fig. 3). This finding suggested that the musculocutaneous nerve was running together with the median nerve in the axilla and then became separated from it at the midhumeral level. The inability to identify the musculocutaneous nerve in the coracobrachialis muscle with ultrasonography and the complete block of both the median and musculocutaneous nerves after injection of local anesthetic around this one structure appeared to confirm this variant anatomy. Anesthesia occurred more slowly in the median nerve. Because the musculocutaneous and median nerves appear to have been fused at this level, fascicles of the former may have been closest to the site of local anesthetic injection. Another explanation is that connective tissue separating the two structures may have limited the diffusion of local anesthetic solution to the median nerve. Appreciation of variations in anatomy is an important regional anesthesia. Failure to understand that the musculocutaneous nerve may run with the median nerve may lead to physician frustration and patient discomfort or injury. In this case, real-time sonographic guidance of axillary block was of benefit in understanding this common anatomical variation and sparing the patient repeated attempts at blocking of the musculocutaneous nerve within the coracobrachialis muscle. If the axillary block had been performed with either nerve stimulation or by transarterial technique, the unusual pattern might not have been appreciated, because injection of local anesthetic within the confines of
544 the neurovascular bundle likely would have produced a successful block.
References [1] Neal JM, Hebl JR, Gerancher JC, et al. Brachial plexus anesthesia: essentials of our current understanding. Reg Anesth Pain Med 2002; 27:402 - 28. [2] Perlas A, Chan VW, Simons M. Brachial plexus examination and localization using ultrasound and electrical stimulation. Anesthesiology 2003;99:429 - 35. [3] Retzl G, Kapral S, Greher M, et al. Ultrasonographic findings of the axillary part of the brachial plexus. Anesth Analg 2001;92:1271 - 5. [4] Delaunay L, Jochum D. Anatomy of the brachial plexus. In: Chelly JE, editor. Peripheral nerve blocks: a color atlas, 2nd ed Philadelphia7 Lippincott Williams and Wilkins; 2004. p. 28 - 38. [5] Spence BC, Sites BD, Beach ML. Ultrasound-guided musculocutaneous nerve block: a description of a novel technique. Reg Anesth Pain Med 2005;30:198 - 201. [6] Bergmann RA, Thompson SA, Afifi AK. Compendium of human anatomic variation. Baltimore7 Urban and Schwarzenberg; 1988.
S.L. Orebaugh, S. Pennington [7] Choi D, Rodriguez-Niedenfuhr M, Vazquez T, et al. Patterns of connections between the musculocutaneous and median nerves in the axilla and arm. Clin Anat 2002;15:11 - 7. [8] Venieratos D, Anagnostopoulou S. Classification of communications between the musculocutaneous and median nerves. Clin Anat 1998; 11:327 - 31. [9] Beheiry EE. Anatomical variations of the median nerve distribution and communication in the arm. Folia Morphol 2004;63: 313 - 8. [10] Schafhalter-Zoppoth I, Gray AT. The musculocutaneous nerve: ultrasound appearance for peripheral nerve block. Reg Anesth Pain Med 2005;30:385 - 90. [11] Loukas M, Aqueelah H. Musculocutaneous and median nerve connections within, proximal and distal to the coracobrachialis muscle. Folia Morphol 2005;64:101 - 8. [12] Eglseder WA Jr, Goldman M. Anatomic variations of the musculocutaneous nerve in the arm. Am J Orthop 1997;26:777 - 80. [13] Rao PV, Chaudhary SC. Absence of musculocutaneous nerve: two case reports. Clin Anat 2001;14:31 - 5. [14] Heinemeyer O, Reimers CD. Ultrasound of radial, ulnar, median and sciatic nerves in healthy subjects and patients with hereditary motor and sensory neuropathies. Ultrasound Med Biol 1999;25: 481 - 5.