Radiol med (2014) 119:135–141 DOI 10.1007/s11547-013-0322-7
ULTRASONOGRAPHY
Ultrasound-guided anterior axilla musculocutaneous nerve block Zinon T. Kokkalis • Andreas F. Mavrogenis • Theodosios Saranteas • Nikolaos A. Stavropoulos Sofia Anagnostopoulou
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Received: 19 April 2012 / Accepted: 28 May 2012 / Published online: 3 December 2013 Ó Italian Society of Medical Radiology 2013
Abstract Purpose This paper presents a technique of ultrasoundguided localisation and block of the musculocutaneous nerve through the anterior wall of the axilla. Materials and methods Twenty patients (7 males and 13 females; mean age, 35 years) had axillary nerve block for upper extremity trauma. With the arm adducted, the ultrasound probe was positioned on the anterior axillary wall; the axillary artery, coracobrachialis and pectoralis major muscles and lateral cord of brachial plexus were visualised in cross section. With continuous imaging of the axillary artery in cross section, the ultrasound probe was slowly moved towards the biceps muscle until the musculocutaneous nerve appeared crossing the coracobrachialis muscle. After ultrasound localisation of the musculocutaneous nerve, the arm was abducted and externally rotated, and the nerve was identified with nerve stimulation and blocked. The quality of sensory and motor nerve block, as well as of ultrasound imaging were evaluated. Results Ultrasound-guided block of the musculocutaneous nerve was excellent and complete in 18 of the 20 Z. T. Kokkalis A. F. Mavrogenis (&) N. A. Stavropoulos First Department of Orthopaedics, Attikon University Hospital, 41 Ventouri Street, 15562 Holargos, Athens, Greece e-mail: [email protected]; [email protected] T. Saranteas Second Department of Anesthesia and Cardiovascular Critical Care, Attikon University Hospital, 41 Ventouri Street, 15562 Holargos, Athens, Greece S. Anagnostopoulou Department of Anatomy, Athens University Medical School, Attikon University Hospital, 41 Ventouri Street, 15562 Holargos, Athens, Greece
patients. In two patients, the musculocutaneous nerve was fused with the median nerve and the nerve block was repeated successfully with the same technique. The quality of ultrasound imaging was excellent in all patients. No patient experienced pain or tourniquet discomfort during surgery, or any other nerve block-related complication. Conclusion The anterior axillary ultrasound view provides for complete nerve block and imaging of the entire course of the musculocutaneous nerve and its relations with adjacent structures with excellent quality. Keywords Musculocutaneous nerve Ultrasound imaging Axillary block Anterior axilla wall
Introduction The axillary block is the most distal block performed on the brachial plexus. It is an excellent choice for hand, wrist, forearm and elbow trauma and for elective surgery. However, because the musculocutaneous nerve leaves the brachial plexus sheath proximal to the site of injection, axillary block often results in inconsistent coverage for tourniquet pain, as well as anaesthesia of the volar aspect of the skin below the elbow that extends to the thenar eminence [1–7]. The musculocutaneous nerve arises from the lateral cord of the brachial plexus, opposite the lower border of the pectoralis major muscle, its fibres being derived from C5, C6 and C7 nerve roots. The median, ulnar and radial nerves all travel with the axillary artery within the axillary sheath [1–4], whereas the musculocutaneous nerve has already left this sheath, crossing the coracobrachialis muscle [5]. Therefore, the musculocutaneous nerve must be blocked separately during an axillary nerve block. However,
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variations and irregularities of the musculocutaneous nerve, such as double, short or absent nerve, adherence or fusion with the median nerve and variable course through or beneath the coracobrachialis and biceps brachii muscle may complicate localisation and blockade of the musculocutaneous nerve in the axilla [1, 2, 6, 7]. Ultrasound-guided nerve block has greatly facilitated nerve localisation and blockade in regional anaesthesia [8– 10], especially for nerves such as the musculocutaneous nerve that do not have predictable relationship to easily identifiable vascular structures [10–14]. Using a standard axillary ultrasound-guided approach to the musculocutaneous nerve, the patient is placed in the supine position with the arm abducted and externally rotated; the ultrasound probe is positioned at the base of the axilla, at the junction of the pectoralis major and biceps muscle [10–12]. The musculocutaneous nerve is found at the juncture between the biceps and coracobrachiales muscle [10–12]. However, anatomical and ultrasound studies have described variations in the exact anatomical location of the musculocutaneous nerve in 0–22 % of cases [7, 15–26]; in these cases, the nerve was outside the coracobrachialis muscle, near the axillary artery, or more frequently near or fused with the median nerve in a common trunk [17, 18]. In addition, using a standard axillary ultrasound-guided approach to the musculocutaneous nerve the position of the nerve outside the coracobrachialis muscle and its course from the lateral cord of the brachial plexus to the biceps brachii muscle could not be detailed [26]. Moreover, the injection needle of the local anaesthetic is brought into the ultrasound beam in the axial section, and could be easily missed as it appears as a small dot in the ultrasound images. To address these problems, we performed this study to present a technique for axillary nerve block of the musculocutaneous nerve using an anterior axillary ultrasoundguided approach.
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Fig. 1 a Position of the ultrasound transducer on the anterior wall of the axilla and b cross-sectional view (PM pectoralis major muscle, Pmi pectoralis minor muscle, CB coracobrachialis muscle, A axillary artery)
Materials and methods Technique Twenty patients had an axillary nerve block for surgical treatment of upper extremity trauma including distal radius fractures (14 patients) and scaphoid fractures (6 patients) from February 2009 to April 2010. There were 7 male and 13 female patients with a mean age of 35 years (range 20–58 years). All axillary nerve blocks were performed using the same technique as described below, by the same anaesthesiologist (T.S.) with an 8-year experience in ultrasound-guided regional anaesthesia. The mean followup was 1 year (range 6 months to 2 years). All patients gave written informed consent to be included in this study. This study was approved by the Institutional Review Board/Ethics Committee of the authors’ institution.
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With the patient in the supine position and the arm adducted (Fig. 1), the ultrasound probe (L12–5, 5–12 MHz, Vivid I and Vivid S6 GE, Waukesha, USA and L9–3, 3–9 MHz, Philips XD 11, Inc., Bothell, WA) was placed on the anterior wall of the axilla; the axillary artery, the coracobrachialis and pectoralis major muscles and the lateral cord of the brachial plexus were visualised in cross section. With continuous imaging of the axillary artery in cross section, the operator slowly moved the ultrasound probe towards the biceps brachii muscle, until the musculocutaneous nerve appeared crossing the coracobrachialis muscle (Fig. 2). After ultrasound localisation
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Fig. 2 a Origin of the musculocutaneous nerve at the lateral cord of the brachial plexus. b The musculocutaneous nerve piercing the coracobrachialis muscle. c The musculocutaneous nerve passing between the coracobrachialis and biceps brachii muscle (PM pectoralis major muscle, CB coracobrachialis muscle, M musculocutaneous nerve, B biceps brachii muscle, L lateral cord, P posterior cord, A axillary artery, V axillary vein)
of the musculocutaneous nerve, the arm was abducted and externally rotated and the nerve was identified with nerve stimulation (eliciting maximal biceps brachii muscle contraction with a 0.5 mA current). A 22-gauge injection needle was advanced in the longitudinal plane of the ultrasound beam, so that the operator could see the entire needle and make adjustments as needed; nerve block was achieved with injection of 8 ml of lidocaine 0.5 %. In the same position of the arm, under ultrasound guidance, the median, ulnar and radial nerves were identified with nerve stimulation and blocked with 25–35 ml of lidocaine 0.5 %.
The quality of sensory and motor block of the musculocutaneous nerve was evaluated 30 min after the anaesthesiologist had performed the axillary block. Motor and sensory block was graded as normal motion/sensation or incomplete block, decreased block and complete block. Inability to move the ipsilateral biceps brachii muscle against gravity was considered the motor block endpoint. Complete absence of pinprick sensation to the lateral aspect of the forearm (lateral antebrachial cutaneous nerve) was considered the sensory block endpoint. The quality of ultrasound imaging of the entire course of the musculocutaneous nerve in the axilla, the axillary artery and vein,
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and the coracobrachialis, pectoralis major and biceps brachii muscles was graded as excellent, difficult or unfeasible. Any complications were recorded.
Results Ultrasound-guided block of the musculocutaneous nerve was complete in 18 of the 20 patients. In these patients, complete sensory and motor block was achieved 30 min after local anaesthetic injection. Ultrasound-guided block of the musculocutaneous nerve was unfeasible and incomplete, respectively, in 2 of the 20 patients. In one patient, the musculocutaneous nerve was fused with the median nerve. In the second patient, the musculocutaneous nerve was not found, and was probably fused with the median nerve. In both these patients, the nerve block was repeated successfully with the same technique. The quality of ultrasound imaging of the musculocutaneous nerve, the axillary artery and vein, the coracobrachialis, biceps brachii and pectoralis major muscles was excellent in all patients, without any difference between the two ultrasound scanners and probes with different resolution used in this series. The musculocutaneous nerve was clearly seen along its entire course from the lateral cord of the brachial plexus, crossing coracobrachialis muscle, to the junction with the biceps brachii muscle. A constellation of hypoechoic grape-like structures with hyperechoic ring was seen on ultrasound images. Fusion of the musculocutaneous with the median nerve was observed in one patient, while in another patient the nerve was not found and was probably also fused with the median nerve. A duplicated axillary vein was observed in one patient. In this patient, the cords of the brachial plexus were irregularly located between the axillary artery and the two axillary veins (Fig. 3). No patient experienced pain or tourniquet discomfort during the surgery. In addition, the next day no patient reported paraesthesia, dysaesthesia, residual anaesthesia, or any other nerve block related complication.
Discussion Traditionally, anatomical landmarks have been used to identify needle insertion sites for nerve blockade [5]. However, the degree to which these landmarks are appreciated depends on multiple variables, such as body habitus, distortion of anatomy from prior surgical operations, ability to position the patient and vascular disease. Therefore, alternative techniques for nerve localisation, such as ultrasound-guided techniques for regional anaesthesia in both the upper and lower extremities have evolved [12, 14, 27, 28]. The advantage of ultrasound-guided nerve block is
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Fig. 3 Brachial plexus between the axillary artery and a duplicated axillary vein. The musculocutaneous and median nerve were fused and pierced by one of the two axillary veins. Inset pulse wave Doppler used for the identification of the axillary vessels (V axillary vein, A axillary artery, M-MCM musculocutaneous-median nerve, P posterior cord, L lateral cord)
that it affords the anaesthesiologist the real-time ability to visualise the target nerve of interest, direct the needle and witness local anaesthetic spread [27]. The musculocutaneous nerve does not have predictable relationship to adjacent structures in the axilla [10–14]; localisation of the nerve is atypical in up to 22 % of axillary blocks [7]. In addition, it is unpredictable based on simple anthropomorphic data [7]. As opposed to a stimulation technique, blockade of the musculocutaneous nerve under ultrasound guidance is more precise. We performed this study to present a technique for axillary block of the musculocutaneous nerve through an anterior approach. Our results showed that this technique provides for excellent localisation of the musculoskeletal nerve and its entire course from the lateral cord of the brachial plexus to the biceps muscle, and complete motor and sensory nerve block. At the axilla, the lateral, medial and posterior cords of the brachial plexus are divided into their terminal nerve branches. Two major nerves originate from each cord. The lateral cord divides into the musculocutaneous nerve and
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the lateral portion of the median nerve, the medial cord divides into the ulnar nerve and the medial portion of the median nerve, and the posterior cord divides into the radial nerve and axillary nerve. The course of the musculocutaneous nerve through coracobrachialis muscle is short. In most arms, the nerve pierces the coracobrachialis muscle and then passes between the biceps brachii and brachialis muscle, supplying each of these muscles [7, 29, 30]. However, in 8–30 % of arms, the musculocutaneous nerve may accompany or fuse with the median nerve, as occurred in 2 of the 20 patients in this series, without entering the coracobrachialis muscle [13]. Because the musculocutaneous nerve travels separately within the belly of the coracobrachialis muscle, it must be blocked separately during an axillary nerve block. In addition, the musculocutaneous nerve presents frequent irregularities; it may be doubled, unusually short or even absent [1, 2, 6]. It may adhere for some distance to the median nerve and then pass outwards, beneath the biceps brachii, instead of through the coracobrachialis muscle, or it may pass under the coracobrachialis or through the biceps brachii muscle [1, 2, 6]. These variations may complicate localisation and blockade of the musculocutaneous nerve in the axilla [7]. Currently, multiple techniques are used to localise the musculocutaneous nerve for local anaesthetic nerve block. These techniques include direct injection into the coracobrachialis muscle, injection along the humerus, paraesthesia seeking, generation of a biceps contraction by use of nerve stimulation, ultrasound, perivascular and transarterial techniques [5, 31]. Historically, practitioners have utilised direct muscle injection with or without the application of either paraesthesias or nerve stimulation [12, 32]. With the paraesthesia-seeking and nerve-stimulating approaches, all four nerves (median, ulnar, radial and musculocutaneous) can be individually identified and anaesthetised in the axilla; both these methods seem to be equally successful. However, in procedures using the nerve-stimulation technique, actual stimulation of the musculocutaneous nerve leads to a more successful outcome than a simple injection into the coracobrachialis muscle. Moreover, the aforementioned techniques rely on anatomical assumptions of normal neural anatomy and on palpation of internal anatomy, such as the coracobrachialis muscle, biceps muscle and axillary artery to guide needle placement [12, 32]. The degree to which these landmarks are appreciated depends on multiple variables, such as body habitus, prior surgical distortion of anatomy, ability to position the patient and vascular disease [12]. Ultrasound guidance is an attractive option for neural structures, such as the musculocutaneous nerve, that do not have predictable relationships to easily identifiable vascular structures [12]. Data are rapidly emerging regarding the improved success rates of ultrasound-guided regional
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anaesthesia in comparison to traditional approaches [33– 36]. Ultrasound allows for the real-time evaluation of neural anatomy, needle position and spread of local anaesthesia. Real-time imaging is important to diagnose an intravascular or an intra-neuronal injection [37]. Ultrasound is conducted in two dimensions: this means that structures can be imaged either in their short-axis or longaxis [12]. The axillary artery is identified as a hypoechoic palatial circle and the transducer is then moved towards the biceps muscle. The nerve is usually targeted in its shortaxis as it lies between the coracobrachialis and biceps muscles. This hyperechoic nerve is extremely easy to visualise because of the surrounding hypoechoic muscle, generating a distinct interface effect. Needle insertion can be done with the in-plane approach (the needle itself is imaged in its long-axis; complete needle visualisation), or the out-of-plane approach (the needle is imaged in its short-axis; limited view, the operator cannot be assured that the needle tip is being imaged in contrast to part of the shaft). The main downside to the in-plane technique is that the ultrasound beam is very thin and it can be frustrating and difficult to continuously maintain needle imaging [32]. The frequency of the ultrasound system is directly related to the resolution of the system [7]. Resolution generally refers to the ability to image structure detail and to distinguish one object from another. Higher the frequency of the ultrasound, the better the resolution [12]. However, higher frequency systems do not penetrate deeply into the body, thus preventing effective imaging of deep structures because of ultrasound attenuation; higher frequency ultrasound attenuates at more superficial depths than lower frequency ultrasound [7]. Since the initial report of a high-resolution ultrasound technique to visualise and block the musculocutaneous nerve [12], no large clinical study on musculocutaneous nerve localisation in the axillary area has been available. In that study [12], the authors identified the musculocutaneous nerve by placing the transducer over the base of the axillary pyramid where the musculocutaneous nerve seems to exit the axillary cavity by piercing the coracobrachialis muscle. An ultrasound study in healthy volunteers described median, ulnar and radial nerve localisations around the axillary artery, but their limited ultrasound resolution rate precluded any musculocutaneous nerve localisation [26]. Other authors described the ultrasound appearance of the musculocutaneous nerve in the axilla to suggest potential areas to target neural block [13]. Currently, musculocutaneous nerves are routinely located during ultrasound-guided axillary blocks [13, 14] using the above standard technique [12]. However, placing the ultrasound probe at the base of the axilla, as per the standard ultrasoundguidance techniques, often makes it difficult to accurately visualise the origin of the musculocutaneous nerve from
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the lateral cord of the brachial plexus, and its relationship with the coracobrachialis muscle [12, 26, 38]. This is due to the fact that the shape of the axilla resembles a truncated pyramid with a broad base and narrow apex [30]. By sliding the ultrasound probe at the base of the axilla and trying to follow the musculocutaneous nerve to the apex, the axillary cavity further narrows; hence, it is almost unfeasible to depict the entire anatomical course of the musculocutaneous nerve from the lateral cord of the brachial plexus to the biceps brachii muscle without having to angulate the ultrasound probe considerably. In this setting, altering the position or angulation of the probe complicates the procedure and obscures the depiction of the anatomical relationships in the axilla. In addition, the relation of the musculocutaneous nerve with the axillary artery depends on the position of the lateral cord of the brachial plexus to the axillary vessels. Placing the probe at the base of the axilla, also makes it difficult to visualise the lateral cord of the plexus, the exit of the musculocutaneous nerve from the lateral cord, the coracobrachialis muscle and the axillary artery because these structures are located deep in the axillary fossa [7, 12, 29, 30, 38]. Last, during injection of the local anaesthetic, if the needle is brought into the ultrasound beam in the axial section, the needle shaft appears as a small dot which can be easily missed. In the present study and our practice, positioning the ultrasound probe on the anterior wall of the axilla provides for crosssection visualisation of the lateral cord of the brachial plexus, the musculocutaneous nerve, the axillary artery and vein and the coracobrachialis muscle. The major advantage of this approach is that the musculocutaneous nerve can be followed throughout its course in the axillary cavity, thus identifying possible variations and abnormalities. Although the probe is slowly brought towards the biceps brachii muscle, the entire course of the musculocutaneous nerve from the brachial plexus cords, crossing the coracobrachialis muscle to its terminal branches, its relationship with the anatomical structures of the axilla, and any anatomical variations can be clearly recognised. Finally, the injection needle is advanced in the longitudinal plane of the ultrasound beam (in-plane technique); therefore, the operator can see the entire needle and make adjustments as needed. We see three limitations in this study: first, this study did not include a control group of patients, and has not been compared with anatomical dissection. We acknowledge that anatomical dissections may be more accurate than ultrasound localisation. However, ultrasound studies are more advantageous by avoiding modifications of the nerve position due to postmortem muscle rigidity or vessel flattening [14, 26]. In addition, we believe that electrical stimulation and blockade of the musculocutaneous nerve confirmed our findings. Second, the resolution of our ultrasound device may have not allowed us to explore the
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thin connections between musculocutaneous and median nerves, which could be observed in up to 46 % of arms in cadavers [23, 25]. However, such connections are usually observed more distal from the axilla [7]. Furthermore, by increasing the resolution of the system (higher MHz), the depth of penetration would have been reduced [23, 25]. Third, we used two different ultrasound scanners and probes with different resolution. However, with the probes used in the present series, no difference was observed regarding imaging quality during the procedure; both ultrasound probes are new generation ones and of the same frequency bandwidth. In conclusion, the technique presented uses an anterior ultrasound axillary view of the musculocutaneous nerve. The advantages of this approach are (1) the musculocutaneous nerve can be followed throughout its course in the axilla, from the cords to the terminal branches, thus identifying possible variations and abnormalities, (2) it allows cross-section visualisation of the lateral cord of the plexus, the musculocutaneous nerve, the axillary artery and vein, and the coracobrachialis muscle and (3) the injection needle is advanced in the longitudinal plane of the ultrasound beam, so the operator can see the entire needle and make adjustments as needed. The quality of ultrasound imaging is excellent, which provides for complete nerve block in most patients. Conflict of interest Zinon T. Kokkalis1, Andreas F. Mavrogenis1, Theodosios Saranteas2, Nikolaos A. Stavropoulos1, Sofia Anagnostopoulou declare no conflict of interest.
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Radiol med (2014) 119:135–141 9. Ivani G, Mosseti V (2009) Pediatric regional anesthesia. Minerva Anestesiol 75:577–583 10. Marhofer P, Harrop-Griffiths W et al (2010) Fifteen years of ultrasound guidance in regional anaesthesia: Part 2-recentdevelopments in block techniques. Br J Anaesth 104:673–683 11. Christophe JL, Berthier F, Boillot A et al (2009) Assessment of topographic brachial plexus nerves variations at the axilla using ultrasonography. Br J Anaesth 103:606–612 12. Spence BC, Sites BD, Beach ML (2005) Ultrasound-guided musculocutaneous nerve block: a description of a novel technique. Reg Anesth Pain Med 30:198–201 13. Schafhalter-Zoppoth I, Gray AT (2005) The musculocutaneous nerve: ultrasound appearance for peripheral nerve block. Reg Anesth Pain Med 30:385–390 14. Perlas A, Chan VW, Simons M (2003) Brachial plexus examination and localization using ultrasound and electrical stimulation: a volunteer study. Anesthesiology 99:429–435 15. Orebaugh SL, Pennington S (2006) Variant localization of the musculocutaneous nerve during axillary nerve block. J Clin Anesth 18:541–544 16. Nakatani T, Tanaka S, Mizukami S (1997) Absence of the musculocutaneous nerve with innervation of coracobrachialis, biceps brachii, brachialis and the lateral border of the forearm by branches from the lateral cord of the brachial plexus. J Anat 191(pt 3):459–460 17. Gumusburun E, Adiguzel E (2000) A variation of the brachial plexus characterized by the absence of the musculocutaneous nerve: a case report. Surg Radiol Anat 22:63–65 18. Aydin ME, Kale A, Edizer M et al (2006) Absence of the musculocutaneous nerve together with unusual innervation of the median nerve. Folia Morphol (Warsz) 65:228–231 19. el-Naggar MM (2001) A study on the morphology of the coracobrachialis muscle and its relationship with the musculocutaneous nerve. Folia Morphol (Warsz) 60:217–224 20. Flatow EL, Bigliani LU, April EW (1989) An anatomic study of the musculocutaneous nerve and its relationship to the coracoid process. Clin Orthop Relat Res 244:166–171 21. Krishnamurthy A, Nayak SR, Venkatraya Prabhu L et al (2007) The branching pattern and communications of the musculocutaneous nerve. J Hand Surg Eur 32:560–562 22. Beheiry EE (2004) Anatomical variations of the median nerve distribution and communication in the arm. Folia Morphol (Warsz) 63:313–318 23. Choi D, Rodriguez-Niedenfuhr M, Vazquez T et al (2002) Patterns of connections between the musculocutaneous and median nerves in the axilla and arm. Clin Anat 15:11–17 24. Venieratos D, Anagnostopoulou S (1998) Classification of communications between the musculocutaneous and median nerves. Clin Anat 11:327–331
141 25. Loukas M, Aqueelah H (2005) Musculocutaneous and median nerve connections within, proximal and distal to the coracobrachialis muscle. Folia Morphol (Warsz) 64:101–108 26. Retzl G, Kapral S, Greher M, Mauritz W (2001) Ultrasonographic findings of the axillary part of the brachial plexus. Anesth Analg 92:1271–1275 27. Marhofer P, Greher M, Kapral S (2005) Ultrasound guidance in regional anesthesia. Br J Anaesth 94:7–17 28. Marhofer P, Schrogendorfer K, Koinig H et al (1997) Ultrasonographic guidance improves sensory block and onset time of three-in-one blocks. Anesth Analg 85:854–857 29. Johnson EO, Vekris M, Demesticha T, Soucacos PN (2010) Neuroanatomy of the brachial plexus: normal and variant anatomy of its formation. Surg Radiol Anat 32:291–297 30. Gosling JA, Harris PF, Whitmore I, Willan P (2002) Axilla. In: Gosling JA, Harris PF, Whitmore I, Willan P (eds) Human anatomy, 4th edn. Mosby, Inc., Edinburgh, pp 70–80 31. Gaertner E, Kern O, Mahoudeau G et al (1999) Block of the brachial plexus by the humeral route. A prospective study in 503 ambulatory patients. Proposal of a nerve-blocking sequence. Acta Anaesth Scand 43:609–613 32. Buckenmaier C, Bleckner L (eds) (2012) Axillary block. In: Military advanced regional anesthesia and analgesia (MARAA) handbook, Chap10. Available at http://www.arapmi.org/maraabook-project/Chapt10.pdf. Accessed May 20 33. Kapral S, Greher M, Huber G et al (2008) Ultrasonographic guidance improves the success rate of interscalene brachial plexus blockade. Reg Anesth Pain Med 33:253–258 34. Perlas A, Brull R, Chan VW et al (2008) Ultrasound guidance improves the success of sciatic nerve block at the popliteal fossa. Reg Anesth Pain Med 33:259–265 35. Chan VW, Perlas A, McCartney J et al (2007) Ultrasound guidance improves success rate of axillary brachial plexus block. Anesthesiology 106:992–996 36. Williams SR, Chovinard P, Arcand G et al (2003) Ultrasound guidance speeds execution and improves the quality of supraclavicular block. Anesth Analg 97:1518–1523 37. Sites BD, Chan VW, Neal JM et al (2010) The American Society of Regional Anesthesia and Pain Medicine and the European Society of Regional Anaesthesia and Pain Therapy joint committee recommendations for education and training in ultrasoundguided regional anesthesia. Reg Anesth Pain Med 35(2 Suppl): S74–S80 38. Bargallo´ X, Carrera A, Sala-Blanch X et al (2010) Ultrasoundanatomic correlation of the peripheral nerves of the upper limb. Surg Radiol Anat 32:305–314
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ULTRASONOGRAPHY
Ultrasound-guided anterior axilla musculocutaneous nerve block Zinon T. Kokkalis • Andreas F. Mavrogenis • Theodosios Saranteas • Nikolaos A. Stavropoulos Sofia Anagnostopoulou
•
Received: 19 April 2012 / Accepted: 28 May 2012 / Published online: 3 December 2013 Ó Italian Society of Medical Radiology 2013
Abstract Purpose This paper presents a technique of ultrasoundguided localisation and block of the musculocutaneous nerve through the anterior wall of the axilla. Materials and methods Twenty patients (7 males and 13 females; mean age, 35 years) had axillary nerve block for upper extremity trauma. With the arm adducted, the ultrasound probe was positioned on the anterior axillary wall; the axillary artery, coracobrachialis and pectoralis major muscles and lateral cord of brachial plexus were visualised in cross section. With continuous imaging of the axillary artery in cross section, the ultrasound probe was slowly moved towards the biceps muscle until the musculocutaneous nerve appeared crossing the coracobrachialis muscle. After ultrasound localisation of the musculocutaneous nerve, the arm was abducted and externally rotated, and the nerve was identified with nerve stimulation and blocked. The quality of sensory and motor nerve block, as well as of ultrasound imaging were evaluated. Results Ultrasound-guided block of the musculocutaneous nerve was excellent and complete in 18 of the 20 Z. T. Kokkalis A. F. Mavrogenis (&) N. A. Stavropoulos First Department of Orthopaedics, Attikon University Hospital, 41 Ventouri Street, 15562 Holargos, Athens, Greece e-mail: [email protected]; [email protected] T. Saranteas Second Department of Anesthesia and Cardiovascular Critical Care, Attikon University Hospital, 41 Ventouri Street, 15562 Holargos, Athens, Greece S. Anagnostopoulou Department of Anatomy, Athens University Medical School, Attikon University Hospital, 41 Ventouri Street, 15562 Holargos, Athens, Greece
patients. In two patients, the musculocutaneous nerve was fused with the median nerve and the nerve block was repeated successfully with the same technique. The quality of ultrasound imaging was excellent in all patients. No patient experienced pain or tourniquet discomfort during surgery, or any other nerve block-related complication. Conclusion The anterior axillary ultrasound view provides for complete nerve block and imaging of the entire course of the musculocutaneous nerve and its relations with adjacent structures with excellent quality. Keywords Musculocutaneous nerve Ultrasound imaging Axillary block Anterior axilla wall
Introduction The axillary block is the most distal block performed on the brachial plexus. It is an excellent choice for hand, wrist, forearm and elbow trauma and for elective surgery. However, because the musculocutaneous nerve leaves the brachial plexus sheath proximal to the site of injection, axillary block often results in inconsistent coverage for tourniquet pain, as well as anaesthesia of the volar aspect of the skin below the elbow that extends to the thenar eminence [1–7]. The musculocutaneous nerve arises from the lateral cord of the brachial plexus, opposite the lower border of the pectoralis major muscle, its fibres being derived from C5, C6 and C7 nerve roots. The median, ulnar and radial nerves all travel with the axillary artery within the axillary sheath [1–4], whereas the musculocutaneous nerve has already left this sheath, crossing the coracobrachialis muscle [5]. Therefore, the musculocutaneous nerve must be blocked separately during an axillary nerve block. However,
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variations and irregularities of the musculocutaneous nerve, such as double, short or absent nerve, adherence or fusion with the median nerve and variable course through or beneath the coracobrachialis and biceps brachii muscle may complicate localisation and blockade of the musculocutaneous nerve in the axilla [1, 2, 6, 7]. Ultrasound-guided nerve block has greatly facilitated nerve localisation and blockade in regional anaesthesia [8– 10], especially for nerves such as the musculocutaneous nerve that do not have predictable relationship to easily identifiable vascular structures [10–14]. Using a standard axillary ultrasound-guided approach to the musculocutaneous nerve, the patient is placed in the supine position with the arm abducted and externally rotated; the ultrasound probe is positioned at the base of the axilla, at the junction of the pectoralis major and biceps muscle [10–12]. The musculocutaneous nerve is found at the juncture between the biceps and coracobrachiales muscle [10–12]. However, anatomical and ultrasound studies have described variations in the exact anatomical location of the musculocutaneous nerve in 0–22 % of cases [7, 15–26]; in these cases, the nerve was outside the coracobrachialis muscle, near the axillary artery, or more frequently near or fused with the median nerve in a common trunk [17, 18]. In addition, using a standard axillary ultrasound-guided approach to the musculocutaneous nerve the position of the nerve outside the coracobrachialis muscle and its course from the lateral cord of the brachial plexus to the biceps brachii muscle could not be detailed [26]. Moreover, the injection needle of the local anaesthetic is brought into the ultrasound beam in the axial section, and could be easily missed as it appears as a small dot in the ultrasound images. To address these problems, we performed this study to present a technique for axillary nerve block of the musculocutaneous nerve using an anterior axillary ultrasoundguided approach.
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Fig. 1 a Position of the ultrasound transducer on the anterior wall of the axilla and b cross-sectional view (PM pectoralis major muscle, Pmi pectoralis minor muscle, CB coracobrachialis muscle, A axillary artery)
Materials and methods Technique Twenty patients had an axillary nerve block for surgical treatment of upper extremity trauma including distal radius fractures (14 patients) and scaphoid fractures (6 patients) from February 2009 to April 2010. There were 7 male and 13 female patients with a mean age of 35 years (range 20–58 years). All axillary nerve blocks were performed using the same technique as described below, by the same anaesthesiologist (T.S.) with an 8-year experience in ultrasound-guided regional anaesthesia. The mean followup was 1 year (range 6 months to 2 years). All patients gave written informed consent to be included in this study. This study was approved by the Institutional Review Board/Ethics Committee of the authors’ institution.
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With the patient in the supine position and the arm adducted (Fig. 1), the ultrasound probe (L12–5, 5–12 MHz, Vivid I and Vivid S6 GE, Waukesha, USA and L9–3, 3–9 MHz, Philips XD 11, Inc., Bothell, WA) was placed on the anterior wall of the axilla; the axillary artery, the coracobrachialis and pectoralis major muscles and the lateral cord of the brachial plexus were visualised in cross section. With continuous imaging of the axillary artery in cross section, the operator slowly moved the ultrasound probe towards the biceps brachii muscle, until the musculocutaneous nerve appeared crossing the coracobrachialis muscle (Fig. 2). After ultrasound localisation
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Fig. 2 a Origin of the musculocutaneous nerve at the lateral cord of the brachial plexus. b The musculocutaneous nerve piercing the coracobrachialis muscle. c The musculocutaneous nerve passing between the coracobrachialis and biceps brachii muscle (PM pectoralis major muscle, CB coracobrachialis muscle, M musculocutaneous nerve, B biceps brachii muscle, L lateral cord, P posterior cord, A axillary artery, V axillary vein)
of the musculocutaneous nerve, the arm was abducted and externally rotated and the nerve was identified with nerve stimulation (eliciting maximal biceps brachii muscle contraction with a 0.5 mA current). A 22-gauge injection needle was advanced in the longitudinal plane of the ultrasound beam, so that the operator could see the entire needle and make adjustments as needed; nerve block was achieved with injection of 8 ml of lidocaine 0.5 %. In the same position of the arm, under ultrasound guidance, the median, ulnar and radial nerves were identified with nerve stimulation and blocked with 25–35 ml of lidocaine 0.5 %.
The quality of sensory and motor block of the musculocutaneous nerve was evaluated 30 min after the anaesthesiologist had performed the axillary block. Motor and sensory block was graded as normal motion/sensation or incomplete block, decreased block and complete block. Inability to move the ipsilateral biceps brachii muscle against gravity was considered the motor block endpoint. Complete absence of pinprick sensation to the lateral aspect of the forearm (lateral antebrachial cutaneous nerve) was considered the sensory block endpoint. The quality of ultrasound imaging of the entire course of the musculocutaneous nerve in the axilla, the axillary artery and vein,
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and the coracobrachialis, pectoralis major and biceps brachii muscles was graded as excellent, difficult or unfeasible. Any complications were recorded.
Results Ultrasound-guided block of the musculocutaneous nerve was complete in 18 of the 20 patients. In these patients, complete sensory and motor block was achieved 30 min after local anaesthetic injection. Ultrasound-guided block of the musculocutaneous nerve was unfeasible and incomplete, respectively, in 2 of the 20 patients. In one patient, the musculocutaneous nerve was fused with the median nerve. In the second patient, the musculocutaneous nerve was not found, and was probably fused with the median nerve. In both these patients, the nerve block was repeated successfully with the same technique. The quality of ultrasound imaging of the musculocutaneous nerve, the axillary artery and vein, the coracobrachialis, biceps brachii and pectoralis major muscles was excellent in all patients, without any difference between the two ultrasound scanners and probes with different resolution used in this series. The musculocutaneous nerve was clearly seen along its entire course from the lateral cord of the brachial plexus, crossing coracobrachialis muscle, to the junction with the biceps brachii muscle. A constellation of hypoechoic grape-like structures with hyperechoic ring was seen on ultrasound images. Fusion of the musculocutaneous with the median nerve was observed in one patient, while in another patient the nerve was not found and was probably also fused with the median nerve. A duplicated axillary vein was observed in one patient. In this patient, the cords of the brachial plexus were irregularly located between the axillary artery and the two axillary veins (Fig. 3). No patient experienced pain or tourniquet discomfort during the surgery. In addition, the next day no patient reported paraesthesia, dysaesthesia, residual anaesthesia, or any other nerve block related complication.
Discussion Traditionally, anatomical landmarks have been used to identify needle insertion sites for nerve blockade [5]. However, the degree to which these landmarks are appreciated depends on multiple variables, such as body habitus, distortion of anatomy from prior surgical operations, ability to position the patient and vascular disease. Therefore, alternative techniques for nerve localisation, such as ultrasound-guided techniques for regional anaesthesia in both the upper and lower extremities have evolved [12, 14, 27, 28]. The advantage of ultrasound-guided nerve block is
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Fig. 3 Brachial plexus between the axillary artery and a duplicated axillary vein. The musculocutaneous and median nerve were fused and pierced by one of the two axillary veins. Inset pulse wave Doppler used for the identification of the axillary vessels (V axillary vein, A axillary artery, M-MCM musculocutaneous-median nerve, P posterior cord, L lateral cord)
that it affords the anaesthesiologist the real-time ability to visualise the target nerve of interest, direct the needle and witness local anaesthetic spread [27]. The musculocutaneous nerve does not have predictable relationship to adjacent structures in the axilla [10–14]; localisation of the nerve is atypical in up to 22 % of axillary blocks [7]. In addition, it is unpredictable based on simple anthropomorphic data [7]. As opposed to a stimulation technique, blockade of the musculocutaneous nerve under ultrasound guidance is more precise. We performed this study to present a technique for axillary block of the musculocutaneous nerve through an anterior approach. Our results showed that this technique provides for excellent localisation of the musculoskeletal nerve and its entire course from the lateral cord of the brachial plexus to the biceps muscle, and complete motor and sensory nerve block. At the axilla, the lateral, medial and posterior cords of the brachial plexus are divided into their terminal nerve branches. Two major nerves originate from each cord. The lateral cord divides into the musculocutaneous nerve and
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the lateral portion of the median nerve, the medial cord divides into the ulnar nerve and the medial portion of the median nerve, and the posterior cord divides into the radial nerve and axillary nerve. The course of the musculocutaneous nerve through coracobrachialis muscle is short. In most arms, the nerve pierces the coracobrachialis muscle and then passes between the biceps brachii and brachialis muscle, supplying each of these muscles [7, 29, 30]. However, in 8–30 % of arms, the musculocutaneous nerve may accompany or fuse with the median nerve, as occurred in 2 of the 20 patients in this series, without entering the coracobrachialis muscle [13]. Because the musculocutaneous nerve travels separately within the belly of the coracobrachialis muscle, it must be blocked separately during an axillary nerve block. In addition, the musculocutaneous nerve presents frequent irregularities; it may be doubled, unusually short or even absent [1, 2, 6]. It may adhere for some distance to the median nerve and then pass outwards, beneath the biceps brachii, instead of through the coracobrachialis muscle, or it may pass under the coracobrachialis or through the biceps brachii muscle [1, 2, 6]. These variations may complicate localisation and blockade of the musculocutaneous nerve in the axilla [7]. Currently, multiple techniques are used to localise the musculocutaneous nerve for local anaesthetic nerve block. These techniques include direct injection into the coracobrachialis muscle, injection along the humerus, paraesthesia seeking, generation of a biceps contraction by use of nerve stimulation, ultrasound, perivascular and transarterial techniques [5, 31]. Historically, practitioners have utilised direct muscle injection with or without the application of either paraesthesias or nerve stimulation [12, 32]. With the paraesthesia-seeking and nerve-stimulating approaches, all four nerves (median, ulnar, radial and musculocutaneous) can be individually identified and anaesthetised in the axilla; both these methods seem to be equally successful. However, in procedures using the nerve-stimulation technique, actual stimulation of the musculocutaneous nerve leads to a more successful outcome than a simple injection into the coracobrachialis muscle. Moreover, the aforementioned techniques rely on anatomical assumptions of normal neural anatomy and on palpation of internal anatomy, such as the coracobrachialis muscle, biceps muscle and axillary artery to guide needle placement [12, 32]. The degree to which these landmarks are appreciated depends on multiple variables, such as body habitus, prior surgical distortion of anatomy, ability to position the patient and vascular disease [12]. Ultrasound guidance is an attractive option for neural structures, such as the musculocutaneous nerve, that do not have predictable relationships to easily identifiable vascular structures [12]. Data are rapidly emerging regarding the improved success rates of ultrasound-guided regional
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anaesthesia in comparison to traditional approaches [33– 36]. Ultrasound allows for the real-time evaluation of neural anatomy, needle position and spread of local anaesthesia. Real-time imaging is important to diagnose an intravascular or an intra-neuronal injection [37]. Ultrasound is conducted in two dimensions: this means that structures can be imaged either in their short-axis or longaxis [12]. The axillary artery is identified as a hypoechoic palatial circle and the transducer is then moved towards the biceps muscle. The nerve is usually targeted in its shortaxis as it lies between the coracobrachialis and biceps muscles. This hyperechoic nerve is extremely easy to visualise because of the surrounding hypoechoic muscle, generating a distinct interface effect. Needle insertion can be done with the in-plane approach (the needle itself is imaged in its long-axis; complete needle visualisation), or the out-of-plane approach (the needle is imaged in its short-axis; limited view, the operator cannot be assured that the needle tip is being imaged in contrast to part of the shaft). The main downside to the in-plane technique is that the ultrasound beam is very thin and it can be frustrating and difficult to continuously maintain needle imaging [32]. The frequency of the ultrasound system is directly related to the resolution of the system [7]. Resolution generally refers to the ability to image structure detail and to distinguish one object from another. Higher the frequency of the ultrasound, the better the resolution [12]. However, higher frequency systems do not penetrate deeply into the body, thus preventing effective imaging of deep structures because of ultrasound attenuation; higher frequency ultrasound attenuates at more superficial depths than lower frequency ultrasound [7]. Since the initial report of a high-resolution ultrasound technique to visualise and block the musculocutaneous nerve [12], no large clinical study on musculocutaneous nerve localisation in the axillary area has been available. In that study [12], the authors identified the musculocutaneous nerve by placing the transducer over the base of the axillary pyramid where the musculocutaneous nerve seems to exit the axillary cavity by piercing the coracobrachialis muscle. An ultrasound study in healthy volunteers described median, ulnar and radial nerve localisations around the axillary artery, but their limited ultrasound resolution rate precluded any musculocutaneous nerve localisation [26]. Other authors described the ultrasound appearance of the musculocutaneous nerve in the axilla to suggest potential areas to target neural block [13]. Currently, musculocutaneous nerves are routinely located during ultrasound-guided axillary blocks [13, 14] using the above standard technique [12]. However, placing the ultrasound probe at the base of the axilla, as per the standard ultrasoundguidance techniques, often makes it difficult to accurately visualise the origin of the musculocutaneous nerve from
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the lateral cord of the brachial plexus, and its relationship with the coracobrachialis muscle [12, 26, 38]. This is due to the fact that the shape of the axilla resembles a truncated pyramid with a broad base and narrow apex [30]. By sliding the ultrasound probe at the base of the axilla and trying to follow the musculocutaneous nerve to the apex, the axillary cavity further narrows; hence, it is almost unfeasible to depict the entire anatomical course of the musculocutaneous nerve from the lateral cord of the brachial plexus to the biceps brachii muscle without having to angulate the ultrasound probe considerably. In this setting, altering the position or angulation of the probe complicates the procedure and obscures the depiction of the anatomical relationships in the axilla. In addition, the relation of the musculocutaneous nerve with the axillary artery depends on the position of the lateral cord of the brachial plexus to the axillary vessels. Placing the probe at the base of the axilla, also makes it difficult to visualise the lateral cord of the plexus, the exit of the musculocutaneous nerve from the lateral cord, the coracobrachialis muscle and the axillary artery because these structures are located deep in the axillary fossa [7, 12, 29, 30, 38]. Last, during injection of the local anaesthetic, if the needle is brought into the ultrasound beam in the axial section, the needle shaft appears as a small dot which can be easily missed. In the present study and our practice, positioning the ultrasound probe on the anterior wall of the axilla provides for crosssection visualisation of the lateral cord of the brachial plexus, the musculocutaneous nerve, the axillary artery and vein and the coracobrachialis muscle. The major advantage of this approach is that the musculocutaneous nerve can be followed throughout its course in the axillary cavity, thus identifying possible variations and abnormalities. Although the probe is slowly brought towards the biceps brachii muscle, the entire course of the musculocutaneous nerve from the brachial plexus cords, crossing the coracobrachialis muscle to its terminal branches, its relationship with the anatomical structures of the axilla, and any anatomical variations can be clearly recognised. Finally, the injection needle is advanced in the longitudinal plane of the ultrasound beam (in-plane technique); therefore, the operator can see the entire needle and make adjustments as needed. We see three limitations in this study: first, this study did not include a control group of patients, and has not been compared with anatomical dissection. We acknowledge that anatomical dissections may be more accurate than ultrasound localisation. However, ultrasound studies are more advantageous by avoiding modifications of the nerve position due to postmortem muscle rigidity or vessel flattening [14, 26]. In addition, we believe that electrical stimulation and blockade of the musculocutaneous nerve confirmed our findings. Second, the resolution of our ultrasound device may have not allowed us to explore the
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thin connections between musculocutaneous and median nerves, which could be observed in up to 46 % of arms in cadavers [23, 25]. However, such connections are usually observed more distal from the axilla [7]. Furthermore, by increasing the resolution of the system (higher MHz), the depth of penetration would have been reduced [23, 25]. Third, we used two different ultrasound scanners and probes with different resolution. However, with the probes used in the present series, no difference was observed regarding imaging quality during the procedure; both ultrasound probes are new generation ones and of the same frequency bandwidth. In conclusion, the technique presented uses an anterior ultrasound axillary view of the musculocutaneous nerve. The advantages of this approach are (1) the musculocutaneous nerve can be followed throughout its course in the axilla, from the cords to the terminal branches, thus identifying possible variations and abnormalities, (2) it allows cross-section visualisation of the lateral cord of the plexus, the musculocutaneous nerve, the axillary artery and vein, and the coracobrachialis muscle and (3) the injection needle is advanced in the longitudinal plane of the ultrasound beam, so the operator can see the entire needle and make adjustments as needed. The quality of ultrasound imaging is excellent, which provides for complete nerve block in most patients. Conflict of interest Zinon T. Kokkalis1, Andreas F. Mavrogenis1, Theodosios Saranteas2, Nikolaos A. Stavropoulos1, Sofia Anagnostopoulou declare no conflict of interest.
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