|OJHAS Vol. 21, Issue 2:
A Rare Variation in the Course of C5 Root of Brachial Plexus
Satheesha B Nayak, Department of Basic Medical Sciences, Manipal Academy of Higher Education, Madhav Nagar, Manipal, Karnataka State, India,
Soumya Kodimajalu Vasudeva, Department of Mathematics, Manipal Institute of Technology, Manipal Academy of Higher Education, Madhav Nagar, Manipal, Karnataka State, India.
Address for Correspondence
Dr. Soumya KV,
Assistant Professor (Senior Scale),
Department of Mathematics,
Manipal Institute of Technology,
Manipal Academy of Higher Education,
Madhav Nagar, Manipal,
Karnataka State, India - 576104
Nayak SB, Soumya KV. A Rare Variation in the Course of C5 Root of Brachial Plexus. Online J Health Allied Scs.
2022;21(2):16. Available at URL:
Submitted: Jun 2,
2022; Accepted: Jul 2, 2022; Published: Jul 30, 2022
Abstract: Variations in the formation of the upper trunk of the brachial plexus are relatively rare. Knowledge of its possible variation is useful to orthopedic surgeons dealing with the problems of cervical spine, anesthesiologists performing brachial plexus blocks and general surgeons performing lower neck surgeries. In this report, we present a variation in the formation of the upper trunk of the brachial plexus. The upper trunk was formed by the union of ventral rami of fifth and sixth cervical spinal nerves. The fifth cervical ventral ramus passed ventral to the scalanus anterior muscle, while the sixth cervical ventral ramus passed between the scalanus anterior and medius muscles. The upper trunk was formed at the lateral border of the scalenus anterior muscle.
Key Words: Brachial plexus, upper trunk, scalenus anterior, variation, Erb’s point
Brachial plexus is formed by the union of ventral primary rami of fifth, sixth, seventh, eighth cervical spinal nerves and the ventral ramus of the first thoracic spinal nerve. The upper trunk of brachial plexus is formed by the union of ventral rami of fifth and sixth cervical spinal nerves; the middle trunk by continuation of the ventral ramus of seventh cervical spinal nerve and the lower trunk by the union of ventral rami of eighth cervical and first thoracic spinal nerves. The trunks of brachial plexus are situated between the scalenus anterior and medius muscles along with the subclavian artery, which is the lowermost in position. After emerging out from the scalene muscles, the trunks divide in to anterior and posterior divisions and the divisions reunite to form lateral, medial and posterior cords of brachial plexus. Trunks of brachial plexus seldom show variations. Upper trunk may not be formed in a few cases. In a study by Uysal et al. (2003), upper trunk was not formed in 1% of cases . Absence of upper trunk has also been reported by Adam et al. (2011). . In some cases, formation of the upper trunk by the sixth and seventh cervical ventral rami has been reported . Nayak et al. (2005) have reported a rare variation of formation of upper trunk by union of ventral rami of fifth, sixth and seventh cervical spinal nerves . Reports are also available on two and four trunked brachial plexuses [5, 6]. We report a rare pattern of course of roots of upper trunk. This report could be of interest to anatomists, neurologists, orthopedic surgeons and anesthesiologists.
During routine dissection classes for undergraduate medical students, we observed a variation in the course of the roots that form the upper trunk of brachial plexus. The variation was found in the left side of the neck of a male cadaver aged approximately 65 years. The variation was unilateral. After emerging out of the intervertebral foramen, the fifth cervical ventral ramus passed downward and laterally, anterior to the scalenus anterior muscle. The sixth cervical ventral ramus passed between scalenus anterior and medius muscles. The two roots joined to form the upper trunk at the lateral border of the scalenus anterior muscle (Figure 1). Further, the upper trunk gave its two branches; suprascapular nerve and nerve to subclavius in front of the scalenus medius muscle and then divided into its anterior and posterior divisions. Thus only the middle and lower trunks were situated between the scalene muscles. There were no other observable variations in the neck.
Figure 1. Dissection of the lower part of the left side of the neck, showing the variation in the formation of the brachial plexus.
(EJV – external jugular vein; IJV – internal jugular vein; PN – phrenic nerve; CL – clavicle; OH – inferior belly of omohyoid; SA – scalenus anterior; SM – scalenus medius; UT – upper trunk of brachial plexus; MT – middle trunk of brachial plexus; C5 – C5 root of upper trunk; C6 – C6 root of upper trunk; NS – nerve to subclavius; SSN – suprascapular nerve; CP – cervical plexus)
Upper trunk of brachial plexus is also known as Erb’s point. Upper trunk injuries can happen when the person falls on shoulder or stab injuries of lower neck. Iatrogenic injuries of the roots of the upper trunk are possible when it presents variations in the course of the rootlets or variations in the contributions to its formation. C5 palsy is one of the common complications after cervical decompression. Presence of a variation like the one being reported here, might increase the chances of injury . Ultrasound guided brachial plexus blocks are usually performed during the upper limb surgeries. A variation like the current one might lead to improper anesthesia as te upper trunk is formed at the outer border of scalenus anterior and its C5 root passed in front of the scalenus anterior muscles . C5 root has been reported to pass through scalenus anterior in about 6% of cases . and anterior to the scalenus anterior in less than 3% cases . Location of C5 root anterior to scalenus anterior might prompt iatrogenic injuries during orthopedic fixation of the lower cervical spine or in administration of anesthesia to the brachial plexus. The knowledge of this variation could be useful for general surgeons while clearing deep cervical lymph nodes. C5 root might also get involved in therapeutic blockage of the phrenic nerve as the root is anterior to scalenus anterior, along with the phrenic nerve.
The passage of C5 root of brachial plexus anterior to scalenus anterior is very rare. It is liable to injury during orthopedic procedure and cervical lymph node clearance. This variation might lead to ineffective brachial plexus anesthesia also.
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