Variant insertion of coracobrachialis muscle-morphological significance, embryological basis and clinical importance

Abstract

The coracobrachialis muscle in the arm is morphologically the sole representative of adductor group muscle in the arm, but such function during the process of evolution became insignificant in man. It is more important morphologically than functionally. Variant insertion of the coracobrachialis muscle was found during routine dissection of an adult male cadaver in the Department of Anatomy, College of Medical Sciences, and Bharatpur, Nepal.Normally the coracobrachialis muscle is inserted into the middle of the medial border of the humerus. In the present case an additional slender tendon passed inferiorly, crossing anterior to the median nerve and brachial artery, before attaching to the medial epicondyle of the humerus. Most of the proximal part of the tendon gave rise to an aponeurotic expansion that inserted into the distal medial border of the humerus. The tendinous insertion and aponeurotic expansion may represent a variant of the coracobrachialis longus (Wood's) muscle and the internal brachial ligament or the ligament of Struthers. The ulnar nerve was found to be traversing below the aponeurotic expansion. This type of anomalous insertion of coracobrachialis muscle may lead to compression of median nerve, brachial artery and ulnar nerve.

The co-occurrence of a four-headed coracobrachialis muscle, split coracoid process and tunnel for the median and musculocutaneous nerves: the potential clinical relevance of a very rare variation

“…In some primates, the CBM is composed of two parts, which is roughly equivalent to the coracobrachialis brevis. In man, it is formed of a single part; this may derive from the coracobrachialis medius of the lower animals, or from the fusion of the two heads observed in apes and prosimians; in the latter case, the MCN would be trapped between them [ 19 , 51 ].…”

A Study of Upper Limb Muscle Anomalies and Their Effects on the Neurovascular Structures

“…Guha et al [20] in his report describes an additional slender tendon which passed inferiorly, crossing anterior to the median nerve and brachial artery, before attaching to the medial epicondyle of the humerus.…”

Nerve Entrapment in the Osseoaponeurotic Tunnel Mimicking Struther’s Ligament Associated With Superficial Brachial Artery: An Embryological Error

“…The muscle primordia within the different layers of the arm at a certain stage of development, fuse to form a single muscle mass, thereafter, some muscle primordial disappear through cell death. Failure of muscle primordial to disappear during embryologic development may account for the presence of the accessory insertion of coracobrachialis muscle [16]. Variations of muscle may be a result of altered molecular interaction between the mesenchymal cells [19,20].…”

“…The lower head is usually suppressed in man, and is sometimes represented by a fibrous band called the "Ligament of Struthers" or "Internal brachial ligament" which extends from supratrochlear spur to medial epicondyle. If this is present, median nerve or brachial artery or both may pass beneath it and might compress them producing vascular spasm or median nerve palsy [6][7][8][9][10][11][12][13][14][15][16][17]. The axillary artery becomes the brachial artery at the lower border of the tendon of the teres major muscle.…”