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Journal of the Anatomical Society of India

Variation of the Lateral Cord of Brachial Plexus Piercing Coracobrachialis Muscle

Author(s): Abhaya, A; Khanna J. and Prakash R.

Vol. 52, No. 2 (2003-07 - 2003-12)

Department of Anatomy, University College of Medical Sciences & G.T.B. Hospital, Shahdara, Delhi. INDIA


Anomalies in the formation of lateral cord of brachial plexus and the communication between its branches are being observed commonly but the variation of the course of lateral cord is not much reported in the literature. The present report describes a unilateral rare course of the lateral cord piercing the coracobrachialis muscle, observed in the infraclavicular part of brachial plexus during routine gross anatomy dissection of right axilla and arm region of an 80 years old Indian male cadaver. The frequency of anomalies found in the arrangement and distribution of lateral cord and its branches makes this anatomic region complicated with regard to surgical approaches. The clinical importance of the variation in light of its development is discussed.

Key words: Lateral cord, brachial plexus, coracobrachialis muscle.


Variations of the lateral cord of brachial plexus regarding composition of fibre bundle and absence or communication between its branches are common and being reported by several authors (Kerr, 1918, Linell, 1921; Miller, 1934; Hollinshead, 1966; Tsikaras et al. 1983; Iwamoto et al. 1990; Sargon et al. 1995; Nakatani et al, 1997; Sud and Sharma, 2000; Chouhan and Roy, 2002; Choi et al. 2002). The fibres from the median nerve may accompany the musculocutaneous as it transits the coracobrachialis muscle (Kaus and Wotowicz, 1995; Williams et al, 1995; Venieratos and Anagnostopoulou, 1998; Sevki et al, 2001), but very rarely the lateral cord pierces the coracobrachialis and then divide into musculocutaneous and the lateral root of median nerve (Le Minor, 1990).

Normally the union of the ventral rami of the fifth, sixth, seventh and eighth cervical nerves and first thoracic nerve form the brachial plexus. These rami unit, divide and unit again to form the trunks, anterior and posterior divisions and the cords of brachial plexus and ultimately these cords and their branches appear in the axilla grouped around the axillary artery (Hollinshead, 1979).

The lateral cord gives its first branch the lateral pectoral nerve to the pectoralis major muscle and then divides into musculocutaneous and lateral root of median nerve. The musculocutaneous nerve pierces the coracobrachialis muscle and passes obliquely to the lateral side of the arm between the biceps brachii and the brachialis muscle, also supplying their musculature. Later it pierces the deep facia above elbow lateral to the tendon of the biceps brachii and continues as the lateral cutaneous nerve of the forearm. Median nerve is formed anterior or anterolateral to axillary artery by the union of its two roots. The lateral root of median nerve is the largest branch of the lateral cord of brachial plexus while the medial root arises from the medial cord and crosses in front of the axillary artery to join the lateral root. After joining of both roots the median nerve descends anterior to the axillary artery and upper part of brachial artery to reach the medial aspect of brachial artery in the distal half of the arm (Williams et al, 1995).

The variations of the lateral cord of brachial plexus should be kept in consideration while performing surgical exploration of the axilla and arm region to avoid damage to these important nerves.

Case Report:

During educational gross anatomy dissection of embalmed cadaver in the department of Anatomy, University College of Medical Sciences, Delhi it was observed in the infraclavicular part of brachial plexus of right upper limb of an 80 years old Indian male, that the lateral cord pierced the coracobrachialis muscle from its medial side, lateral to axillary artery at 92mm from the tip of coracoid process. The first branch of the lateral cord, the lateral pectoral nerve was arising normally just below the outer border of the first rib. It passed anterior to axillary artery and vein and supplied the deep surface of pectoralis major muscle. The other two branches of the normal diameter emerged out from the coracobrachialis muscle at different places. The lateral root of median nerve emerged from the anterior aspect of the coracobrachialis muscle at 102mm from the tip of coracoid process and joined the medial root of median nerve arising from the medial cord of brachial plexus at 155mm to form the main trunk of median nerve while the musculocutaneous nerve emerged from the lateral side of coracobrachialis muscle, lateral to the exit of lateral root of median nerve at 110 mm from the tip of coracoid process.

On exploring of the passage of lateral cord within the coracobrachialis muscle it was found that it split into musculocutaneous and lateral root of median nerve at 96mm from coracoid process and the branch to the coracobrachialis muscle arose from musculocutaneous nerve at 98 mm from the tip of the coracoid process. The lateral root of median nerve did not give any branch within the muscle and no communication was observed between musculocutaneous and lateral root of median nerve within the coracobrachialis muscle or in the later course of these two nerves. The relations of all the three cords of brachial plexus with the second part of axillary artery and the further course, branching and termination of musculocutanous and median nerver in arm, forearm and hand followed the normal pattern. The other limb of the cadaver did not show any such variation of the lateral cord and was absolutely normal in relation, formation and branching pattern of brachial plexus. No other arterial or muscular variation was observed in either of the limbs.


Coracobrachialis is a flexor muscle of the arm and is vulnerable to the injury from the retractors placed under the coracoid muscles as required during shoulder reconstructive surgery. The operative management by coracoid graft transfers in the recurrent dislocations of shoulder and shoulder arthroscopies could be the source of lesions to the structures piercing the muscle. (Flatow et al, 1989; Laburthe-Tolra, 1994-95). The muscle has been suggested for possible use as flap for coverage in infraclavicular defects of exposed axillary vessels, especially in postmastecomy reconstructive surgery (Hober et al, 1990).

The interpretation of the anomaly of the atypical course of lateral cord requires consideration of the development and innervation of upper limb musculature. Muscles of the limbs are derived from somatic precursor muscle cells from the ventrolateral edges of the somites opposite the developing limbs, which lie lateral to the neural tube and causes bulge in the overlying ectoderm. Somites have a specific effect on the position of the developing spinal nerves, which preferentially grow through the cranial half of sclerotome. Spinal nerves are derived from two sources, the motor nerve from the neural tube and the sensory nerves from the neural crest (Williams et al, 1995). The nerve cords from the spinal nerves that correspond to the early extent of limb buds grow distally to establish an intimate contact with the differentiating mesodermal condensations into intermuscular spaces and end in a premuscle mass. As suggested by Sannes et al (2000) that the guidance of the developing axons is regulated by expression of chemoattractants and chemorepulsants in a highly coordinated site specific fashion. Any alterations in signaling between mesenchymal cells and neuronal growth cones can lead to significant variations and probably in this case causes the lateral cord to pass through the coracobrachialis muscle. Once formed,any developmental differences would persist postnatally. (Brown et al. 1991; Arey, 1966).

The knowledge of the course and distribution of the lateral cord of brachial plexus, keeping in mind the variations in anatomy and the level of penetration are important while performing neurotization of the brachial plexus lesions, shoulder arthroscopy by anterior glenohumeral portal and shoulder reconstructive surgery.


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Missing Image


Photograph of the dissected right axilla and upper arm showing the branches of brachial plexus. Note the entry of lateral cord (LC) of brachial plexus into coracobrachialis muscle (CB) and their different exits, the lateral root of median nerve (LR) emerges out from the anterior aspect (Black arrow) while the musculocutaneous (MC) from the lateral side of the coracobrachialis to supply biceps brachii (BB) and brachialis muscle (BR).


Missing Image


Schematic diagram of figure. 1, Note the nerve to biceps brachii (NBB) and brachialis (NBR) from the musculocutaneous nerve (MC). AA-axillary artery, MR and LR = medial root and lateral root of median nerve (MN). UN- ulnar nerve and MCN-medial cutaneous nerve of forearm.

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