The co-occurrence of a four-headed coracobrachialis muscle, split coracoid process and tunnel for the median and musculo
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ANATOMIC VARIATIONS
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 Łukasz Olewnik1 · Nicol Zielinska1 · Piotr Karauda1 · Fabrice Duparc3 · Georgi P. Georgiev4 · Michał Polguj2 Received: 15 April 2020 / Accepted: 15 September 2020 © The Author(s) 2020
Abstract The coracobrachialis muscle (CBM) originates from the apex of the coracoid process, in common with the short head of the biceps brachii muscle, and from the intermuscular septum. Both the proximal and distal attachment of the CBM, as well as its relationship with the musculocutaneus nerve demonstrate morphological variability, some of which can lead to many diseases. The present case study presents a new description of a complex origin type (four-headed CBM), as well as the fusion of both the short biceps brachii head, brachialis muscle and medial head of the triceps brachii. In addition, the first and second heads formed a tunnel for the musculocutaneus and median nerves. This case report has clear clinical value due to the split mature of the coracoid process, and is a significant indicator of the development of interest in this overlooked muscle. Keywords Anatomical variations · Coracobrachialis muscle · Median nerve · Musculocutaneus nerve · Split coracoid
Introduction
* Łukasz Olewnik [email protected] Nicol Zielinska [email protected] Piotr Karauda [email protected] Fabrice Duparc fabrice.duparc@univ‑rouen.fr Georgi P. Georgiev [email protected] Michał Polguj [email protected] 1
Department of Anatomical Dissection and Donation, Medical University of Lodz, Lodz, Poland
2
Department of Normal and Clinical Anatomy, Medical University of Lodz, Lodz, Poland
3
Laboratory of Anatomy, Faculty of Medicine, Rouen University, Mont‑Saint‑Aignan, France
4
Department of Orthopaedics and Traumatology, Medical University of Sofia, Sofia, Bulgaria
The flexor compartment of the arm contains the biceps brachii, brachialis and coracobrachialis (CBM) muscles. The CBM originates from the apex of the coracoid process, in common with the short head of the biceps brachii muscle (BBM), and from the intermuscular septum. It inserts by means of a flat tendon into an impression at the middle of the medial surface and border of the body of the humerus, between the origins of the triceps brachii and brachialis muscles [32]. The CBM is innervated by the musculocutaneous nerve (MCN) [32]. The role of the CBM is twofold: it flexes and adducts the arm at the glenohumeral joint, and prevents the arm from being deviated from the frontal plane during abduction. Therefore, during contraction, the CBM causes shoulder flexion by drawing the humerus forward, and shoulder adduction by drawing it toward the torso. It also turns the humerus slightly inwards, thus causing internal rotation. The CBM also stabilizes the humeral head within the shoulder joint, especially when the arm ha
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