|Year : 2012 | Volume
| Issue : 2 | Page : 70-77
A study of the formation and branching pattern of brachial plexus and its variations in adult human cadavers of north Karnataka
Sheetal V Pattanshetti, PS Jevoor, VS Shirol, Daksha Dixit, Shilpa Bhimalli
Department of Anatomy, J N Medical College, Belgaum, Karnataka, India
|Date of Web Publication||1-Oct-2012|
Sheetal V Pattanshetti
Department of Anatomy, J N Medical College, Belgaum, Karnataka
Source of Support: None, Conflict of Interest: None
Introduction and Objectives: The brachial plexus is highly variable, in its formation and branching pattern thus, knowledge of its anatomical patterns, may be insufficient for the surgeon operating on or around these nerves or for the regional anesthesiologist working in this area. Therefore, the present study was an attempt to study further about variations of brachial plexus encountered during routine dissection classes. Materials and Methods: The present descriptive study was carried out by dissection of 60 upper limbs of 30 cadavers, in the age group of 18 to 85 years, obtained during a study period of 2 years from the Department of Anatomy. The plexus was studied in its entire course commencing from the formation in cervical region, course through root of the neck and axilla, up to the main terminal branches of the upper extremity. During the dissection, variations of brachial plexus pertaining to its formation from the roots, trunks, divisions and cords and the branching pattern were observed and data was collected. Results: Out of the 60 cadaveric upper limbs studied for the anatomical variations of the brachial plexus, 2 limbs (3.33%) were pre-fixed plexuses. Fusion of adjacent trunks was detected in 2 limbs (3.33%). Variations in branches of lateral cord were detected in 8 limbs (13.33%). Among Posterior cord variations 2-thoracodorsal nerves were detected in 2 limbs (3.33%). All the other branches from brachial plexus had been found to have no anatomical variations. Conclusion: In the present study, an attempt has been made to know the possible variations of the brachial plexus. Though the variations mentioned may not alter the normal functioning of the limb of the individual, but knowledge of the variations is of prime importance to be kept in mind, during anaesthetic and surgical procedures.
Keywords: Axillary artery, brachial plexus, cadaver
|How to cite this article:|
Pattanshetti SV, Jevoor P S, Shirol V S, Dixit D, Bhimalli S. A study of the formation and branching pattern of brachial plexus and its variations in adult human cadavers of north Karnataka. J Sci Soc 2012;39:70-7
|How to cite this URL:|
Pattanshetti SV, Jevoor P S, Shirol V S, Dixit D, Bhimalli S. A study of the formation and branching pattern of brachial plexus and its variations in adult human cadavers of north Karnataka. J Sci Soc [serial online] 2012 [cited 2017 Mar 25];39:70-7. Available from: http://www.jscisociety.com/text.asp?2012/39/2/70/101846
| Introduction|| |
The brachial plexus is a complex network of nerves, which extends from the neck to the axilla and supplies motor, sensory, and sympathetic fibers to the upper extremity. In the brachial plexus, the intricate manner in which anastomotic connections are formed, give rise to the nerves of extensive cutaneous and motor supply with successions of separations and conjunctions, accounts for the numerous variations, which in some instances may be salient.
The brachial plexus literally means arm braid and is situated in the posterior triangle of the cervical region and in the axilla. This plexus is a union of the lower four cervical (C5, C6, C7, and C8) ventral rami and the first thoracic (T1) ventral ramus. At the lateral border of the anterior scalene muscle, the five roots unite to form the upper, middle and lower trunks, each of which splits into anterior and posterior divisions in the floor of the posterior triangle of the neck. At the upper border of the first rib, the divisions join to form lateral, medial and posterior cords. Just distal to the inferior border of the pectoralis minor muscle, near the third part of the axillary artery (AA), the cords give off their terminal branches, including the axillary, musculocutaneous, radial, median and ulnar nerves. ,,,
The frequency of variations found in the arrangement and distribution of the branches in the brachial plexus, make this anatomical region extremely complicated. The medical concerns involved with these variations include anaesthetic blocks, surgical approaches, interpreting nervous compressions caused by tumor or trauma, having unexplained clinical symptoms and the possibility of these structures being sometimes irreversibly damaged.
| Materials and Methods|| |
The present descriptive study was carried out by dissection of 60 (30 Right and 30 Left) upper limbs of 30 human cadavers, in the age group of 18 to 85 years, obtained during a study period of two years from the Department of Anatomy, J. N. Medical College, KLE University, Belgaum. Cadavers with deformed or traumatized cervical, axillary and arm regions of upper limbs were excluded in the study. The study was done with permission of Independent Ethics Committee of J. N. Medical College, Belgaum.Dissection was done of the upper arm, axilla and posterior triangle of the neck on same side successively as per Cunningham's manual of practical Anatomy.
The plexus was studied in its entire course from the formation in cervical region, course through root of the neck, axilla and up to the terminal branches into the major nerves of the upper extremity. During the dissection, variations of brachial plexus pertaining to its formation from the roots, trunks, divisions and cords and the branching pattern were observed and data was collected. Photographs were taken under good lighting, using zoom digital camera. Rough schematic diagrams were drawn and photographs were labeled. The data collected in the present study was recorded, tabulated, analyzed and also compared with previous studies.
The following parameters were looked for in the present study of formation and branching patterns of brachial plexus,
- Type of plexus depending upon number of roots
- Number of branches from the roots
- Branches from upper trunk
- Number of divisions from each trunk
- Number of branches from the lateral cord
Number of branches from the medial cord
- Number of branches from the posterior cord
- Formation of median nerve
- Number of roots contributing to median nerve (MN) formation
- Relationship with axillary artery
- Relationship with brachial artery
- Other main terminal branches
- Musculocutaneous nerve (MCN)
- Axillary nerve (AN)
- Radial nerve (RN)
- Ulnar nerve (UN)
- Communicating branches between nerves
| Results and Discussion|| |
The data obtained on different parameters were tabulated and recorded as follows [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12], [Table 13].
|Table 1: Roots (ventral rami of spinal nerves) contributing to formation of brachial plexus|
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Three of the cases in which absence of MCN was detected, also had extra lateral root of median nerve. So the total number of variations detected in branches from lateral cord was in 8 out of 60.
Branch encountered as connection between MCN and MN in axilla or upper 1/3 was considered as second lateral root and in the middle 1/3 or lower 1/3 of arm as a communication.
In absence of MCN, median nerve supplied the muscles of anterior compartment of forearm in 4 specimens
The knowledge of variations in brachial plexus anatomy is important particularly to anatomists, radiologists, anesthesiologists and surgeons and has gained much importance due to the wide use and reliance on computer imaging in diagnostic medicine.  Also, the presence of anatomic variations of the peripheral nervous system is often used to explain unexpected clinical signs and symptoms. Descriptions of nerve variations are useful in clinical/surgical practice since an anatomical variation can be the cause of a nerve palsy syndrome due to different relation of a nerve and a related muscle. In most of these cases, surgery can lead to a rapid recovery of nerve function.  Although a brachial plexus injury during neck surgery is a rare condition, especially due to its protection by a dense layer of deep cervical fascia surrounding the scalenus muscles and also the protection of its roots between the scalenus anterior and scalenus medius muscle, anatomical variations of the brachial plexus may render it vulnerable to injury during routine surgical neck dissection. 
Roots (ventral rami of spinal nerves) contributing to formation of brachial plexus
In the present study out of the 60 cadaveric upper limbs studied for the anatomical variations of the brachial plexus, two limbs (3.33%) were pre-fixed plexuses [Figure 1], 58 limbs (96.67%) were normal and no post-fixed plexus was detected. In a similar study by Uysal I et al. the brachial plexuses were composed mostly of the C5, C6, C7, and C8 nerves and the T1 nerve (71.5%). A prefixed plexus was observed in 25.5% of cases, and a postfixed plexus was observed in 2.5% of cases. In one case (0.5%), the C4 and T2 nerves joined the formation. 
|Figure 1: Left-sided Pre- fixed brachial plexus 1. Ventral ramus of C4. 2) Ventral ramus of C5. 3) Ventral ramus of C6. 4) Upper trunk 5) Ventral ramus of C7. 6) Middle trunk 7) Ventral ramus of C8. 8) Ventral ramus of C8 9) Lower trunk|
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Fusion of adjacent trunks
In our study fusion of adjacent trunks was detected in two limbs (3.33%), where middle and lower trunks were fused which gave common anterior and posterior division and this anterior division split into two parts. The smaller contribution from the first part, joined with anterior division of upper trunk to form lateral cord and larger contribution acted as the medial root of median nerve. Branch to coracobrachialis was also given from first part of common anterior division of fused middle and lower trunks. The second part of anterior division acted as medial cord and gave the ulnar nerve and medial cutaneous nerve of arm and forearm [Figure 2] and [Figure 3]. The posterior division of upper trunk united with the common posterior division of the fused middle and lower trunks to form posterior cord. In one of these cases the axillary nerve, upper subscapular nerve and lower subscapular nerve were formed from posterior division of upper trunk and radial nerve and thoracodorsal nerves from the posterior cord.
|Figure 2: Left-sided brachial plexus showing fusion of middle and lower trunks giving common anterior and posterior divisions|
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|Figure 3: Left-side brachial plexus: Fusion of middle and Lower trunks 1). Upper trunk 2) Middle trunk 3) Lower trunk 4) Fused middle and lower trunk 5) Median nerve 6) Musculocutanneous nerve 7a) and 7b) 1st anterior division and 2nd anterior division from fused middle and lower trunks 8) Posterior cord 9) Axillary nerve 10) Radial nerve 11) Medial cutaneous nerve of forearm 12) Ulnar nerve 13) Anterior division of upper trunk receiving fibres from 7a to form lateral cord|
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Kocabiyik N et al. reported that the anterior divisions of upper and middle trunks united to form the lateral cord lateral to the axillary artery. The anterior division of the lower trunk ran as the medial cord, medial to the axillary artery. Suprascapular nerve did not arise from the superior trunk instead; it arose from the C5 nerve root. Superior subscapular, thoracodorsal and inferior subscapular nerves arose from the posterior division of the upper trunk. Afterwards, the posterior cord continued as axillary and radial nerves. 
Variations in branches from cords
In present study variations in branches of lateral cord were detected in eight limbs, in which extra lateral root of median nerve [Figure 4] was detected in seven limbs (11.67%) and four limbs (6.67%) had absence of musculocutaneous nerve [Figure 5]. Medial cord variation was seen in two limbs (3.33%) both of which did not give the medial root of median nerve but other branches were given normally. The medial root of median nerve was given from the first part of anterior division of fused middle and lower trunks and the second part of the anterior division acted as the medial cord and gave rest of its branches normally. Among Posterior cord variations, two-thoracodorsal nerves were detected in two limbs (3.33%). Both of these nerves arose as direct branches of posterior cord supplying latissimus dorsi. In one limb (1.67%) the posterior cord divided into two branches/roots, which subsequently united to form the radial nerve.
|Figure 4: Right-sided median nerve formation by three roots 1' Brachial artery 2) Medial root of median nerve 3) 1st lateral root of median nerve 4) 2nd lateral root of median nerve 5) Ulnar nerve 6) Median nerve 7) Musculocutaneous nerve 8) Axillary nerve 9) Radial nerve 10) Brachial artery|
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Das S et al. reported anomalous branches of lateral cord crossing the artery anteriorly, which are liable to cause compression symptoms producing ischemia. Such variations are likely to confuse the operating surgeons who usually operate in this region with the standard anatomical knowledge. 
Gupta M et al. observed in his study that anterior division of middle trunk also gave rise to the nerve to coracobrachialis and an additional lateral root of median nerve. 
In the present study of 60 upper limbs musculocutaneous nerve was present in 56 (93.33%) and all of which originated from lateral cord and were lateral to 3 rd part of axillary artery. After the formation of musculocutaneous nerve, it descended down to pierce coracobrachialis in all the cases where it was present. Out of 56 limbs where it was present, in seven limbs (12.5%) there was a communication with the median nerve. In three (5.36%) the communication was before musculocutaneous nerve pierced coracobrachialis and in four (7.14%) after piercing coracobrachilis. Absence of musculocutaneous nerve was detected in 4(6.67%). Several workers have already reported these variations.
Prasad Rao PV and Chaudhary SC observed two cases of absent musculocutaneous nerve in 24 upper limbs. Median nerve took over the area of supply of the musculocutaneous nerve by giving both muscular and sensory branches. 
Venieratos and Anagnostopoulou  classified the communication between two nerves into 3 types.
Type I - Communication between musculocutaneous nerve and median nerve is proximal to the entrance of musculocutaneous nerve into the coracobrachialis
Type II - Communication is distal to the muscle.
Type III - The nerve or communicating branch did not pierce the muscle.
The variation in our study in comparison to Venieratos and Anagnostopoulou classification includes out of 56, Type I-3 (5.36%), Type II-4 (7.14%) and Type III-nil.
After supplying muscles of front of the arm, it continued below as lateral cutaneous nerve of forearm.
Number of roots and level of formation of median nerve
In the present study, the median nerve (MN) was formed from two roots in 53 (88.33%) specimens, of which, level of formation was also recorded. In 41 (68.33%) MN was formed in axilla, in 8 (13.33%) MN was formed in upper third of arm, in 4 (6.67%) MN was formed in middle third of arm. The formation of MN by three roots was detected in seven (11.66%) out of which, in five (8.33%) MN was formed in axilla and in two (3.33%) MN was formed in upper third of arm. Pandey and Shukla  reported in their study of 344 specimens median nerve formation at lower level in 6 (1.7%) limbs. The exact level of formation however has not mentioned.
Formation of median nerve in relation to axillary artery
In our study median nerve was formed lateral to axillary artery (AA) in 46 (76.67%), anterior to AA in 12 (20%) and medial to AA in 2 (3.33%). None of the limbs showed formation of median nerve to be posterior to AA. Pandey and Shukla  reported in their study of 344 axillae have reported formation of median nerve medial to axillary artery in 8 (2.3%) cases.
Course of median nerve in relation to brachial artery
In our study the median nerve coursed lateral to brachial artery in 58 (96.67%) and medial to brachial artery in two (3.33%). The course of MN posterior to brachial artery in was detected in none of the specimens. Nayak S et al. have reported the median nerve to descend medial to brachial artery. 
Innervation of muscles of anterior compartment of arm
In our study musculocutaneous nerve (MCN) was present in 56 (93.33%) and supplied muscles of anterior compartment and in four (6.67%) MCN was found to be absent [Figure 5] and in three out of the 4 specimens where absence of MCN was detected, median nerve was formed by three roots the extra lateral root joined the main nerve at different levels. In one of the cadavers absence of MCN was bilateral and on one of the sides median nerve was formed from three roots. The branches either from lateral roots of median nerve or directly from MN itself innervated biceps brachii, coracobrachialis and brachilis. Guttenberg et al. in their study of 56 upper limbs have noticed absence of musculocutaneus nerve in two (3.6%) upper limbs. 
Communication between MN and MCN
In the present study communicating branches between MN and MCN were in seven cases (11.67%) out of which communication was in the upper third of arm in three (5%) and in middle third of arm in four (6.67%). Our study was confined to the arm region only.
In our study ulnar nerve arose from medial cord of brachial plexus. Many workers described variation in the origin of this nerve. In our study in 58 (96.67%) limbs the nerve arose from medial cord of brachial plexus.
The ulnar nerve was lying medial to third part of axillary artery in all the 60 upper limbs. No variation was observed in this regard. It ran distally through the axilla between axillary artery and vein and was lying medial to brachial artery as far as midarm in all the limbs.
In our study fusion of adjacent trunks was detected in two limbs (3.33%), where middle and lower trunks were fused which gave common anterior and posterior division and this anterior division split into two parts. The first part smaller contribution joined with anterior division of upper trunk to form lateral cord and larger one acted as the medial root of median nerve. The second part of anterior division acted as medial cord and gave the ulnar nerve and medial cutaneous nerve of arm and forearm. The medial pectoral nerve was cut and could not be traced to its origin.
In one of the limb (1.67%) where middle trunk and lower trunk was fused, the ulnar nerve received an abnormal communicating branch from radial nerve. This variation is not well documented from previous investigators. In the middle of the arm the nerve pierced the medial intermuscluar septa. It descended to the forearm by passing posterior to medial epicondyle of humerus.
In our study radial nerve was present in all 60 limbs (100%) originated from posterior cord and was posterior to 3 rd part of axillary artery. Only in one limb (1.67%) thoracodorsal and radial nerve originated from posterior cord, whereas axillary, upper subscapular and lower subscapular originated from posterior division of upper trunk. Posterior division of upper trunk joined common posterior division of fused middle trunk and lower trunk to form posterior cord. The communication between radial and ulnar nerve is not well documented.
In one case (1.67%), there was high division of radial nerve in the arm before passing through the lower triangular space, to enter the spiral groove. In only one limb (1.67%) communication was formed between radial to ulnar. In another case (1.67%) radial nerve was formed from two roots, formed by splitting of the posterior cord, which subsequently united to form radial nerve.
The nerve then descended behind the brachial artery and entered the spiral groove by passing through lower triangular space. On reaching the lateral side of humerus it pierced the lateral intermuscular septum and came to lie in front of lateral epicondyle of humerus. Atkan et al.  reported a case in which radial nerve arose from the union of posterior divisions of inferior trunk and middle trunk in the left upper extremity.
The axillary nerve divided into two branches-anterior and posterior. The anterior branch supplied anterior part of deltoid and posterior branch supplied posterior part of deltoid and teres minor in all the limbs of our study.
In our study, axillary nerve existed in all 60 limbs (100%), which originated in 59 (98.3%) from posterior cord and in one case (1.67%) from posterior division of upper trunk. In all the cases axillary nerve was formed postero-lateral to 3 rd part of axillary artery and there was no communication with any other nerves. The nerve along with posterior circumflex humeral artery traveled in quadrangular space.
Communicating branches between nerves
In our study, seven limbs (11.67%) had communicating branch was encountered between musculocutaneous and median nerve out of which 3 (5%) were in upper third of arm and 4 (6.67%) in middle third of arm. In one limb (1.67%) there was a communicating branch from radial nerve to ulnar nerve. In 3 (5%) limbs there was communicating branch between MPN and LPN. There was no communicating branch between UN and MN.
Choi D et al reported variations in connections between the musculocutaneous and median nerves in the arm. These variations were seen in 64 cadavers (46.4%). 
| Conclusion|| |
A thorough knowledge of variations of brachial plexus is mandatory in cases like, surgical exploration of axilla and arm, during cervical rib correction, which is a cause for thoracic outlet syndrome, anesthetic block either through, cervical or axillary approach, internal fixation of humeral fracture from common anterior approach and even during orthopedic and neurosurgical procedures on cervical spine and prosthetic implant placements.
The brachial plexus lesions may follow trauma, compression of nerves, shoulder dislocation, iatrogenic damage, and traumatic delivery in infants or malpositioning of patient during anaesthesia.
The neurovascular relations of the Brachial plexus and axillary artery and its branches are intricate and intimate. It is a known fact that the normal and anomalous positions of arteries and veins may be determined pre-operatively by angiographic studies, but in case of nerves it is not possible to detect such an anomaly. It is only at the time of surgery that the surgeon is exposed to such variations. Therefore, as anatomists, we believe, that prior anatomical knowledge of such anomalies may provide great help to neurologists, traumatologists and surgeons.
Injuries could be due to avulsion of the nerve roots from spinal cord, rupture of the nerve (neurotmesis), neuroma by a scar tissue during regeneration of an injured nerve or just compression or stretching (neuropraxia). All of these cause varying degrees of paresthesias, paresis or paralysis which in addition to compromising muscle function and movements hampering activities of the affected limb and can also affect physical appearance as in Erb-Duchenne's and Klumpke's palsy, etc. The importance of having experienced medical experts to treat brachial plexus injuries is thus rightfully emphasized.
In the present study, an attempt has been made to know the possible variations of the brachial plexus. Though the variations mentioned may not alter the normal functioning of the limb of the individual, but knowledge of the variations is of prime importance to be kept in mind, during anesthetic and surgical procedures. We agree that the restricted sample size was a limitation in our study. Yet an earnest effort in the study has opened new avenues for further research. Thus, we would have better guidelines for successful surgical interventions.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12], [Table 13]