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Revista Brasileira de Anestesiologia

Print version ISSN 0034-7094

Rev. Bras. Anestesiol. vol.60 no.6 Campinas Nov./Dec. 2010

http://dx.doi.org/10.1590/S0034-70942010000600007 

SCIENTIFIC ARTICLE

 

Brachial plexus cords: a morphological study

 

 

Ijoni CostabeberI; Gustavo Moura de AlmeidaII; Mônica BeckerIII; Aron Ferreira da SilveiraIV; Dorival Terra MartiniV

IPharmacist, Professor at UFSC
IIMedical Student at UFSC
IIIPhysician, Professor at UFSC
IVVeterinarian, Professor at UFSC
VDentist, Professor at UFSC

Correspondence to

 

 


SUMMARY

BACKGROUND AND OBJECTIVES: The brachial plexus represents an important network of nerves, commonly approached in nerve blocks prior to surgical procedures. Therefore, the knowledge of its anatomy is indispensable so those procedures can be carried out accordingly. The objective of the present study was to analyze the morphology of brachial plexus cords with special emphasis to its topographic relationships.
METHODS: This study was undertaken by dissecting the cervical, axillary, and brachial regions of a human cadaver fixed in 10% phormol, from the Human Anatomy Laboratory of the Morphology Department of Universidade Federal de Santa Maria. Access to the cords was obtained by pushing back the pectoralis minor and pectoralis major muscles, clavicular section, and extraction of part of the subclavius muscle.
RESULTS: Cords originated from the anterior and posterior divisions of the trunks (upper, middle, and lower) of the brachial plexus. The lateral fascicle originated from the anterior divisions of the upper and middle trunks; the posterior, from the posterior divisions of the trunks; and the middle fascicle consisted from the continuation of the anterior division of the lower trunk. The cords showed relationships with the axillary artery, and they were located posteriorly to the pectoralis minor muscle, close to its insertion on the coracoid process.
CONCLUSIONS: The results were in concordance with the anatomical descriptions of classical authors. This study allowed the analysis of the morphology of the brachial plexus cords, demonstrating its main topographic relationships.

Keywords: ANATOMY: brachial plexus.


 

 

INTRODUCTION

The brachial plexus represents an important network of nerve fibers that innervate the upper limbs 1. It is a peripheral structure widely approached in clinical and surgical procedures. Thus, the plexus is evaluated for the diagnosis of orthopedic lesions, such as neurovascular compression of the subclavian artery and the brachial plexus caused by the thoracic outlet syndrome 2. Besides, it is the target of anesthetic blockades for surgeries of the proximal upper limbs, such as interscalene and intersternocleidomastoid anesthesia 3.

Due to those implications, studies to increase and define the morphologic knowledge of segments of the brachial plexus are necessary to work as anatomical substrate for safe interventions on this topography. The objective of the present study was to analyze the morphology of brachial plexus cords, with special attention to its topographic relationships.

 

METHODS

Analysis of the brachial plexus cords was undertaken after dissecting the cervical, axillary, and brachial regions of a human female cadaver, approximately 60 years old, fixed in 10% formaldehyde, from the Human Anatomy Laboratory of the Morphology Department, Universidade Federal Santa Maria. Methodologies currently described were adapted for the dissection of the structures 4,5. Thus, the access to the cords was obtained after dislocating the pectoralis major and minor muscles (and corresponding fascias) on the direction of their insertions and through section of the clavicle and extraction of a segment of the subclavius muscle. We tried to preserve the vasculature to demonstrate the vasculonervous relationship. A pair of curved anatomical scissors was used to obtain cleavage planes, scalpels number 24 for skin incisions and section of muscle fibers, and 11 for the dissection of the cords. Images were captured with a digital camera (Canon Power Shot SD450) and later catalogued. This study represents the partial results of a teaching project whose objective is the anatomical investigation of the brachial plexus to aggregate theoretical-practical material for the study of this anatomic segment, approved by the Ethics on Research Committee of the Universidade Federal de Santa Maria, according to the Presentation Certificate for Ethical Appreciation #0207.0.243.000-08.

 

RESULTS

The brachial plexus was shown to be an extensive nervous network that initiated in the cervical spine and extended until the axilla. It was identified that throughout this path this network is organized in five distinct portions: roots, trunks, divisions, cords, and terminal branches (peripheral nerves) (Figure 1). Thus, the original roots of the plexus correspond to the anterior branches of the lower four cervical nerves (C5-C8) and the first thoracic (T1). After leaving the intervertebral foramen the anterior branch of C5 joins the anterior branch of C6 forming the upper trunk. The anterior branch of C7 constitutes isolatedly the middle trunk. The anterior branch of C8 joins that of T1 to form the lower trunk. Throughout this path, the brachial plexus is located between the anterior and middle scalene muscles. After passing the lateral margin of the anterior scalene muscle the trunks become more superficial, and are crossed anteriorly by the omohyoid muscle. From this point on, the nerve fibers get closer to each other, crossing the posterior aspect of the clavicle and subclavius muscle (cervicoaxillary channel), where each trunk forms two divisions, one anterior and one posterior.

 

 

In its lower course, posteriorly to the pectoralis major muscle and close to the upper border of the pectoralis minor muscle, the trunk divisions form the cords of the brachial plexus (Figure 2). The three posterior divisions join to form the posterior cord that is formed by the fibers from the three trunks (upper, middle, and lower). The anterior divisions of the upper and middle trunks join to form the lateral cord. The anterior division of the lower trunk remains independent and forms the middle cord.

 

 

The cords are located posteriorly to the pectoralis minor muscle, close to its insertion in the coracoid process of the scapula (Figure 2). They have a significant topographic posterior, lateral, and medial relationship with the axillary artery, determining the anatomical designation of the cords (Figure 3). The axillary vein is located anterior to the artery, being similarly covered by the pectoralis major and minor and subclavius muscles. The brachial plexus and axillary vessels are surrounded by a fascial sheath that originates from the fascias of the anterior and middle scalene muscles and extends up to the proximal third of the arm. Peripheral nerves that innervate the muscles of the upper limb and the thoracic wall are the products of the formation of the plexus.

 

 

DISCUSSION

The present study demonstrated that brachial plexus cords originate from the anterior and posterior divisions of the trunks (upper, middle, and lower), in agreement with classical anatomical descriptions 6,7.

Anatomical investigations are elaborated to elucidate the topographical relationships of brachial plexus cords. Thus, the cords represent a reorganization of the trunks when they cross the axilla, inferior to the clavicle and superior to the first rib 8. This area, known as infraclavicular or plexus expansion sector, is delimited below the skin by the pectoralis major and minor muscles, posteriorly to the vasculo nervous bundle by the anterior serratus muscle, and posteriorly by the pleura 9. The findings of the present study confirmed those observations.

Additionally, the cords have relationships (posteriorly, laterally, and medially) with the axillary artery 1. Complementarily, one study with volunteers using MRI images showed that the cords are located 2.5 cm from the center of the axillary artery 9. However, those results are discordant with another description 10 that considered this same relationship with the subclavian artery. Those differences could be explained by the fact that it was not taken into consideration the fact that the subclavian artery is called axillary artery when it crosses the external surface of the first rib 11.

In the present study, it was possible to demonstrate the topographical situation of the cords posteriorly to the pectoralis minor muscle, close to its insertion in the coracoid process 11. This proximity could be due to the position of abduction of the upper limb used to gain access to the cords, allowing the movement of those nervous structures towards the coracoid process. This analysis can be rectified by the fact that the axillary artery and vein, as well as the brachial plexus cords, are surrounded by adipose tissue, which obeys the movements of the upper limb in relation to the thorax 7. This finding could justify the compression of the cords between the tendon of the pectoralis minor muscle and the coracoid process in situations that promote prolonged hyperabduction of the upper limb 1,2.

The present study, therefore, allowed the analysis of the morphology of the brachial plexus cords demonstrating its main topographical relationships, an indispensable knowledge to the judicious use of clinical-surgical techniques on this nervous network.

 

ACKNOWLEDGEMENTS

Gustavo Moura de Almeida acknowledges the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the grant received through the Programa Institucional de Bolsas de Iniciação Científica, and to Professor Ijoni Costabeber, for the Bolsa Produtividade em Pesquisa. The authors would like to extend their special thanks to the Veterinary Medicine student, Émerson Salvagni, for the drawing of Figure 1.

 

REFERENCES

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09. Orebaugh SL, Williams BA - Brachial plexus anatomy: normal and variant. Scient World J, 2009;9:300-312.         [ Links ]

10. Vieira JL - Bloqueio do plexo braquial. Rev Bras Anestesiol, 1995; 45 (n. especial): 106-115 - Atlas de Técnicas de Bloqueios Regionais.         [ Links ]

11. Goffi FS - Técnica Cirúrgica: Bases Anatômicas, Fisiopatológicas e Técnicas da Cirurgia. 4ª Ed, São Paulo, Atheneu, 2004;822.         [ Links ]

 

 

 

Correspondence to:
Profa. Dra. Ijoni Costabeber
Setor de Anatomia Humana, Departamento de Morfologia, Centro de Ciências da Saúde, Universidade Federal de Santa Maria - UFSM
Av. Roraima, nº 1000
97105-900 - Santa Maria, RS
E-mail: ijonicostabeber@gmail.com

Submitted on June 23, 2010.
Approved on June 25, 2010.

 

 

Received from the Universidade Federal de Santa Maria, UFSC, RS, Brasil.