Variation of the brachial plexus roots in the interscalene groove: relevance in interscalene blocks

Abstract

Objectives: The interscalene block is utilized for regional anesthesia of the upper limb, targeting the roots and trunks of the brachial plexus in the interscalene groove. The prevalence of variation, which may affect the success of this block, has not been documented in detail with respect to side and sex, nor has a classification system been proposed.

Methods: Seventy-nine embalmed bodies were dissected bilaterally. The position of the roots and the subclavian artery relative to the anterior scalene muscle was documented and variations were classified according to prevalence. Differences in the prevalence of variation between left and right sides and between males and females were investigated.

Results: The standard position of the nerves and subclavian artery in the interscalene groove (Type 1) was present in 31.6%. Variant positions included the following passing through the belly of the anterior scalene: C5 and C6 roots (Type 2) (46.8%), C5 root (Type 3) (15.2%), C5 and C6 roots as well as the subclavian artery (Type 4) (3.8%), and lastly, C5, C6 and C7 roots (Type 5) (2.5%). Variant anatomy was statistically more prevalent in females on the right side only.

Conclusion: Variant locations of the roots and subclavian artery external to the interscalene groove were common, suggesting that ultrasound should be used to visualize variations prior to performing interscalene blocks. A classification type of variant positions has been developed for standardization. 

Keywords

• anatomical variation; anterior scalene muscle; brachial plexus; brachial plexus roots; interscalene block

References

1. 1. Bruce BG, Green A, Blaine TA, Wesner LV. Brachial plexus blocks for upper extremity orthopaedic surgery. J Am Acad Orthop Surg 2012;20:38–47. 2. Mian A, Chaudhry I, Huang R, Rizk E, Tubbs RS, Loukas M. Brachial plexus anesthesia: a review of the relevant anatomy, complications and anatomical variations. Clin Anat 2014;27:210–21. 3. Jeng C, Rosenblatt M (2010) Upper extremity nerve blocks: techniques. [Internet].[Cited May 9, 2019]. Available from: [https://www. uptodate.com/contents/upper-extremity-nerve-blocks-techniques]. 4. Long TR, Wass CT, Burkle CM. Perioperative interscalene blockade: an overview of its history and current clinical use. J Clin Anesth 2002;14:546–56. 5. Chin KJ, Niazi A, Chan V. Anomalous brachial plexus anatomy in the supraclavicular region detected by ultrasound. Anesth Analg 2008;107: 729–31. 6. Gutton C, Choquet O, Antonini F, Grossi P. Ultrasound-guided interscalene block: influence of anatomic variations in clinical practice. Ann Fr Anesth Reanim 2010;29:770–5. 7. Harry WG, Bennett JDC, Guha SC. Scalene muscles and the brachial plexus: anatomical variations and their clinical significance. Clin Anat 1997;10:250–2. 8. Loukas M, Tubbs RS, Stewart D. An abnormal variation of the brachial plexus with potential clinical significance. West Indian Med J 2008;57:403–5. 9. Matejcik V. Variations of nerve roots of the brachial plexus. Bratisl Lek Listy 2005;106:34–6. 10. Natsis K, Totlis T, Tsikaras P, Anastasopoulos N, Skandalakis P, Koebke J. Variations of the course of the upper trunk of the brachial plexus and their clinical significance for the thoracic outlet syndrome: a study on 93 cadavers. Am Surg 2006;72:188–92. 11. Yadav N. Anatomical variations of the interscalene brachial plexus block: do they really matter? Saudi J Anesth 2014;8:142–3. 12. Inuzuka N. A case of the scalenus anterior muscle passing behind the left subclavian artery. Okajimas Folia Anat Jpn 1989;66:229–40. 13. Halaszynski TM. Ultrasound brachial plexus anesthesia and analgesia for upper extremity surgery: essentials of our current understanding. Curr Opin Anesthesiol 2011;24:581–91. 14. Redman L, Robbs J. Neurogenic thoracic outlet syndrome: are anatomical anomalies significant? S Afr J Surg 2015;53:22–5. 15. Nair AS, Sahoo RK. Implications of pass-over brachial plexus. Anesth Essays Res 2017;11:536–7. 16. Adachi B. Das arterien System der Japaner. Bd 1. Kyoto: Verlag der Kaiserlich-Japanischen Universität zu Tokyo; 1928. p. 506. 17. Kessler JK, Gray AT. Sonography of scalene muscle anomalies for brachial plexus block. Reg Anesth Pain Med 2007;32:172–3. 18. Leonhard V, Landreth R, Caldwell G, Coleman M, Smith H. A new anatomical variation in the brachial plexus roots and its implications for neurogenic thoracic outlet syndrome. FASEB J 2015;29:S1. 19. Chauhan R, Roy TS. Communication between the median and musculocutaneous nerve – a case report. J Anat Soc India 2002;51:72–5. 20. Yang HJ, Gil YC, Lee HY. Intersegmental origin of the axillary artery and accompanying variation in the brachial plexus. Clin Anat 2009;22:586–94. 21. Klaastad O, Sauter AR, Dodgson MS. Brachial plexus block with or without ultrasound guidance. Curr Opin in Anesthesiol 2009;22: 655–60. 22. Roos DB. Thoracic outlet nerve compression. In: Rutherford RB, editor. Vascular surgery. Philadelphia (PA): Saunders; 1989. p. 858– 75.