Clinical significance of the anatomical variations of the brachial plexus

Saraladevi, K V (2006) Clinical significance of the anatomical variations of the brachial plexus. Masters thesis, Stanley Medical College, Chennai.


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INTRODUCTION: The brachial plexus is one of the most complex structure of the peripheral nervous system that supplies the sensory and motor innervation of the upper limb except trapezius muscle. The brachial plexus originates from the ventral rami of fourth to eighth cervical roots and first thoracic root providing motor and sensory innervation. The brachial plexus is formed by the ventral rami of C5, C6, C7, C8 and T1 roots behind the scalenus anterior. Between the scalene anterior and medius in the lower part of posterior triangle, of the five roots the upper two unite to form the upper trunk, the lower two unite to form the lower trunk and the central root continues as the middle trunk. Each trunk divides into anterior and posterior divisions behind the clavicle to supply the flexor and extensor compartments respectively. At the outer border of the first rib, the upper two anterior divisions unite to form the lateral cord, the anterior division of the lower trunk runs as the medial cord, while all the posterior divisions unite to form the posterior cord. These three cords enter the axilla above the first part of the axillary artery, embrace its second part and gives off branches around its third part. The main branches of the cords are; 1. Median nerve - formed by the fusion of a branch from medial cord and a branch from lateral cord (C5, 6, 7, 8, T1). 2. Ulnar nerve - from medial cord (C7, 8, T1). 3. Musculocutaneous nerve - from lateral cord (C5, 6, 7). 4. Radial nerve - from posterior cord (C5, 6, 7, 8, T1). 5. Axillary nerve - from posterior cord (C5, 6). For an anatomist, it is important to facilitate the knowledge of anatomical variations to other allied disciplines. Hence this study focused on the variations of brachial plexus and their impact and chose to disseminate requisite information. MATERIALS OF THE STUDY: 30 embalmed and preserved adult human cadavers. METHOD OF THE STUDY: The study was carried out in 30 embalmed and well preserved human cadavers of both sexes that were kept in for the teaching programme of undergraduate and post graduate medical students at the Department of Anatomy, Stanley Medical College, Chennai by conventional dissection method described in Cunningham’s manual of Practical Anatomy. The incisions were made as per Cunningham’s description figure(10) (incisions 2,3,5). After reflecting skin, superficial fascia and deep fascia in each region the nerves were traced. In the posterior triangle, after removing the fat and fascia of the triangle and also the fascia from the inferior belly of omohyoid, the muscle was turned up; the upper part of the brachial plexus was traced between the scalenus medius and anterior backwards to its roots. The supra scapular nerve and dorsal scapular nerve piercing the scalenus medius were traced deep to omohyoid and trapezius respectively. The long thoracic nerve was dissected from its origin from the back of roots of brachial plexus towards the axilla. The roots of brachial plexus were dissected after reflecting or detaching the scalenus anterior. The dissection was proceeded down after cutting the middle third of clavicle. The clavicular head of pectoralis major was cut, then reflected to observe the lateral pectoral nerve where it pierced the clavipectoral fascia. The medial pectoral nerve was dissected as it entered the pectoralis major after piercing through the pectoralis minor. OBSERVATION: The brachial plexus in 60 human cadaveric specimens were observed from the level of origin to the level of termination in the following aspects: • The formation of the trunks, divisions and cords. • Their relation with the nearby structures viz., muscles, vessels. • The various branches from supraclavicular and infraclavicular parts. • The communication between the nerves. • The course of the branches. • The level of distribution. • The number of branches. Of these above mentioned parameters, only the median nerve showed 19 variations in seventeen specimens out of 60 specimens. The rest of the brachial plexus showed the classical normal anatomical descriptions. These variations of the median nerve were also not of the same, but different on various parameters. Even a single variant is not of the same character in different specimens. Hence every variant specimen of both right and left sides was photographed, labeled and described individually. The specimens showing the variations include Sp.No.1, 2, 8, 9, 13, 18, 24, 27, 30, 38, 41, 43, 45, 46, 48, 51, 55. CONCLUSION: The knowledge of Anatomy in defining the normal structure as well as the variation in each region based on various parameters is always valuable for clinical application. From my study, I noted the variations of brachial plexus especially the median nerve in most of the specimens on different aspects consisting of 1. The high level as well as low level formation of the median nerve. 2. The median nerve was having a communication with the musculocutaneous nerve. 3. The median nerve was passing behind or between the branches of the brachial artery. 4. The median nerve was passing deep to the anomalous fibrous arch in the arm. 5.the median nerve was supplying anterior compartment muscles of the arm. 6. The median nerve was associated with the persistent median artery and terminated in the forearm. 7. The median nerve was showing a communication with the ulnar nerve in the palm. 8. The median nerve was supplying only the radial 2½ fingers. These variations were also reported in the previous studies as a common entity, but the incidence might be different. The previous experts had done these studies in large number of specimens and I am yet to do in more number of specimens. Anyhow the common variation what I found was also noted as a common variant by the experts. So the knowledge of these variations should be kept in mind during surgeries because these are the regions which are approached quiet frequently by the general surgeons, plastic surgeons, oncologists and anaesthesiologist. I conclude by saying that “Among the brachial plexus, the median nerve shows variations frequently on various aspects. So as an Anatomist, it is my duty to stress upon the knowledge of this to the surgeons while performing surgeries and also to the physicians while interpretating unusual clinical presentations”.

Item Type: Thesis (Masters)
Uncontrolled Keywords: Clinical significance, anatomical variations, brachial plexus.
Subjects: MEDICAL > Anatomy
Depositing User: Subramani R
Date Deposited: 05 Oct 2019 05:04
Last Modified: 05 Oct 2019 05:04

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