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. 2020 Feb 26;17(1):50–54. doi: 10.1177/1558944720906510

The 2-Dimensional and 3-Dimensional Anatomy of the Adult Brachial Plexus Divisions and Cords

Junot H S Neto 1,2,✉, Bernardo C Neto 3,4, Andre B D Eiras 1, Renato H S Botelho 1, Jose M de M Carmo 1,3, Marco Aurélio R F Passos 3
PMCID: PMC8721799  PMID: 32100569

Abstract

Background: The objective of this work was to perform a critical review of the 2-dimensional and 3-dimensional anatomy of the adult brachial plexus divisions and cords. Methods: Twelve adult brachial plexuses from fresh cadavers were dissected. All were male and aged between 30 and 50 years. Only corpses without brachial plexus injuries were selected. The purpose of the dissections was to identify the origin of the anterior and posterior divisions of the adult brachial plexus in their respective trunks, as well as the positioning of the posterior, lateral, and medial cords. Results: The posterior division of all trunks had a cranial and dorsal origin, while the anterior division of all trunks had a caudal and ventral origin. The posterior cord was the most cranial of all, the lateral cord was central, and the medial cord was the most caudal of all cords. The posterior division of the superior trunk was always between the suprascapular nerve and the anterior division. Conclusions: Brachial plexus diagrams in most textbooks and papers are different from what was found in our dissections. Contrary to the known diagram, the posterior divisions always had a cranial origin in the superior, middle, and inferior trunks.

Keywords: anatomy, brachial plexus, adult, divisions, cords

Introduction

The brachial plexus is formed by the ventral rami of the spinal nerves of C5, C6, C7, C8, and T1. It is divided into 5 anatomical sessions known as roots, trunks, divisions, cords, and terminal branches. The superior trunk is formed by the union of C5 and C6 roots, C7 root continues as the middle trunk, and the inferior trunk is formed by the union between C8 and T1 roots. Each trunk will give rise to a posterior and anterior division. The posterior division of all trunks forms the posterior cord, the anterior division of the superior and middle trunk forms the lateral cord, and the anterior division of the inferior trunk continues as the medial cord. 1 The brachial plexus can receive contributions from other roots as C4 in 22% of cases 2 or T2 in 1% of cases. 3

Wilfred Harris 4 dissected the brachial plexuses of 60 adults and stated that the posterior division of the superior trunk always had a cranial origin. It always lies between the suprascapular nerve and the anterior division. In 1904, he warned the scientific community that the illustrations of the brachial plexus in most books and articles with the anterior division between the suprascapular nerve and the posterior division were incorrect. In contrast to Wilfred Harris, 4 Uysal et al 5 dissected 200 fetal brachial plexuses and demonstrated that the posterior divisions of the superior and middle trunk had a caudal origin. So, for them, the anterior division of the superior trunk will be situated between the suprascapular nerve and the posterior division. Kirik et al, 6 and Albertoni et al 7 also dissected fetal brachial plexus and reached the same conclusions as Uysal et al. 5

It was a surprise when we realized that a reference book for hand surgery specialists 8 had 2 different illustrations to describe the brachial plexus. The illustration of children’s brachial plexus had similarities with the brachial plexus described by Wilfred Harris, 4 while the adult brachial plexus illustration had similarities to the brachial plexus described by Uysal et al, 5 Kirik et al, 6 and Albertoni et al. 7 This disagreement in the literature led the authors to conduct this research.

Material and Methods

Twelve adult brachial plexuses from donated fresh cadavers were dissected. All were male and aged between 30 and 50 years. Only corpses without brachial plexus injuries were selected. The purpose of the dissections was to identify the origin of the anterior and posterior divisions of the brachial plexus in their respective trunks (superior, middle, and inferior trunks), as well as the positioning of the posterior, lateral, and medial cords.

The bodies were placed in a supine position; the arm was adducted and traction applied in an inferior direction to allow the posterior triangle to open out. We used the extended access to the brachial plexus with a longitudinal supraclavicular incision over the sternocleidomastoid border, a transverse supraclavicular incision over the clavicle followed inferiorly by the deltopectoral groove. The supraclavicular plexus was approached first, to visualize the roots of the plexus. The incision was made just deep to the skin to divide the platysma. Immediately deep to the platysma, the supraclavicular nerves were encountered. The deep fascia was divided along the line of the incision, and a few fibers of the clavicular head of the sternomastoid muscle were divided distally. Below this muscle, the omohyoid was also divided. The fascial layer lying on top of the scaleni was incised, allowing the plexus to come into view. The infraclavicular incision was made through the skin, subcutaneous tissue, and clavipectoral fascia up to the clavicle. The tendon of the pectoralis minor was then identified, lifted, and divided to immediately exposing the entire length of the infraclavicular plexus. In all cases, we performed clavicle osteotomy.

Results

The posterior division of all trunks had a cranial and dorsal origin, while the anterior division of all trunks had a caudal and ventral origin. The posterior cord was the most cranial of all; the lateral cord was central, and the medial cord was the most caudal of all cords. The posterior division of the superior trunk was always between the suprascapular nerve and the anterior division (Figures 1-3).

Figure 1.

Figure 1.

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Adult brachial plexus dissection. Red arrows: superior trunk; yellow arrows: middle trunk; pink arrows: inferior trunk; black arrows: posterior divisions; black circles: posterior cord; orange circles: lateral cord; white circles: medial cord.

Figure 2.

Figure 2.

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Two-dimensional illustration of the adult brachial plexus.

Figure 3.

Figure 3.

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Three-dimensional illustration of the superior trunk. Blue: superior trunk; green: suprascapular nerve; orange: posterior division; yellow: anterior division.

Discussion

Leonardo di Ser Piero da Vinci (Leonardo Da Vinci) was one of the first to represent in modern illustrations the anatomy of the brachial plexus. In his illustrations, the posterior divisions of all trunks had a cranial origin, while all anterior divisions had a caudal origin. The posterior cord was the most cranial, the lateral cord was central, and the medial cord was caudal.9,10 Leonardo da Vinci’s drawings had the same anatomy as those found in our dissections.

There is significant confusion in the literature regarding the anterior and posterior divisions of the superior trunk. Part of this confusion can be caused by the way we draw and teach anatomy, perhaps because of the convenience of always drawing or representing the brachial plexus in the same way as we see in most textbooks and papers.6,11-26 This confusion probably dates from the time of Vesalius (1555), his illustration of the brachial plexus has the same anatomy as published in most books and articles to date. 27 There were differences in brachial plexus illustrations described by Wilfred Harris 4 and Uysal et al, 5 Kirik et al, 6 and Albertoni et al. 7 However, it is essential to emphasize that while Wilfred Harris 4 dissected adult brachial plexuses; Uysal et al, 5 Kirik et al, 6 and Albertoni et al. 7 dissected fetal brachial plexuses. Possibly there are anatomical differences between the adult and fetal brachial plexus that justify 2 different illustrations. However, more studies need to be done to determine if there are anatomical differences between the adult and child brachial plexus.

We were not the first to realize that brachial plexus designs do not correctly represent the origin of the posterior division of the superior trunk. An example of this was Wilfred Harris 4 who alone fought against all the other thinkers of his day to change this knowledge but was unsuccessful. Several authors described the posterior division of the superior trunk with a cranial origin like us.4,9,10,27-31 Some authors were radical in their conclusions; Hanna, 31 for example, stated that the illustrations of the brachial plexus urgently need to be corrected because the posterior division of the superior trunk is always situated between the suprascapular nerve and the anterior division. We share this same opinion; however, it was possible to identify in our dissections that not only the posterior division of the superior trunk had a cranial origin, but all posterior divisions of the adult brachial plexus had a cranial origin concerning their respective trunks (Figure 4).

Figure 4.

Figure 4.

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Three-dimensional illustration of trunks, divisions and cords of adult brachial plexus. Black: superior trunk; blue: middle trunk; white: inferior trunk; green: suprascapular nerve; orange: posterior divisions; yellow: anterior divisions; red: posterior cord; brown: lateral cord; pink: inferior cord.

Through personal communication with several surgeons familiar with the brachial plexus anatomy, we conclude that none of them follow the known illustration of the brachial plexus as the basis for surgery. They do not believe that the illustrations represent the real anatomy, because they all know that the posterior division of the superior trunk arises between the suprascapular nerve and the anterior division. We also share the opinion that brachial plexus illustrations do not represent the correct anatomy found in the surgical field. We always found the origin of the posterior division of the superior trunk between the suprascapular nerve and the anterior division (Figure 5). Moreover, we always found all the posterior divisions of the adult brachial plexus with a cranial origin concerning their respective trunks.

Figure 5.

Figure 5.

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Surgical image of the superior trunk. Blue: superior trunk; green: suprascapular nerve; orange: posterior division; yellow: anterior division. Confirmed by electrical stimulation.

Conclusion

Brachial plexus diagrams in most textbooks and papers are different from what was found in our dissections. In our series of 12 adult brachial plexus dissections, the posterior division of all the trunks always had a cranial and dorsal origin, while the anterior division had a caudal and ventral origin. The posterior cord was always superior, the lateral cord was always central, and the medial cord was always inferior.

Footnotes

Ethical Approval: This study was approved by our institutional review board.

Statement of Human and Animal Rights: All procedures followed were in accordance with the ethical standards of the committee responsible for (institutional and national) human experimentation and with the Helsinki Declaration of 1975, revised in 2008.

Statement of Informed Consent: No consent was required. The medical ethics committee did not request the use of statement of informed consent because it is a study without personal information or experiments.

Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

ORCID iD: Junot H. S. Neto Inline graphic https://orcid.org/0000-0001-9258-0708

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