A proposal for a new classification of coracobrachialis muscle morphology

Bartłomiej Szewczyk,Michał Podgórski,Fabrice Duparc,Michał Polguj,Friedrich Paulsen,Łukasz Olewnik,Piotr Karauda

doi:10.1007/s00276-021-02700-1

Abstract

IntroductionThe coracobrachialis muscle (CRM) originates from the apex of the coracoid process, in common with the short head of the biceps brachii muscle, and from the intermuscular septum. It inserts to the medial part of the humerus between the attachment of the medial head of the triceps brachii and the brachial muscle. Both the proximal and distal attachments of the CRM, as well as its relationship with the musculocutaneus nerve, demonstrate morphological variability.Material and methodsOne hundred and one upper limbs (52 left, and 49 right) fixed in 10% formalin solution were examined.ResultsThree main types, with subtypes, were identified. The most common was Type I (49.5), characterized by a single muscle belly with a classical origin from the coracoid process, medially and posteriorly to the tendon of the biceps brachii. Type II (42.6%), characterized by two heads, was divided into two subtypes (A-B) depending on its origin: Type IIA, where one head originated from the coracoid process posteriorly to the tendon of the biceps brachii and the second head from the short head of the biceps brachii, and Type IIB, in which both heads originated from the coracoid process; however, the superficial head fused with the insertion of a short head of the biceps brachii, while the deep head was directly originating. Finally, Type III (7.9%) was characterized by three heads: two originated from the coracoid process (superficial and deep), and the third from a short head of the biceps brachii. Two types of insertion and two types of musculocutaneous nerve (MCN) relative to CRM could be distinguished.ConclusionAn adapted classification is needed for all clinicians working in this area, as well as for anatomists. The CRM demonstrates morphological variability in both its proximal and distal attachments, as well as the variable course of the MCN relative to the CRM.What is known about this subject "and" What this study adds to existing knowledgeNot much is known about the variability of coracobrachialis muscle. The present paper introduces a completely new classification, both clinical and anatomical.

Highlights

The coracobrachialis muscle (CRM) originates from the apex of the coracoid process, in common with the short head of the biceps brachii muscle, and from the intermuscular septum
– Type I (49.5%)—single belly originating from the coracoid process, medially and posteriorly to the tendon of the short head of the biceps brachii muscles (shBB) (50 cases: 30 female and 20 male; 22 right and 28 left)—Figs. 1, 4a
Type IIa—one head originating from the coracoid process posteriorly to the tendon of the biceps brachii and a second head originating from the shBB (22 cases: 13 females and 9 males; 11 right and 11 left)—Figs. 2a, 4b

Summary

Introduction

The coracobrachialis muscle (CRM) originates from the apex of the coracoid process, in common with the short head of the biceps brachii muscle, and from the intermuscular septum. It inserts to the medial part of the humerus between the attachment of the medial head of the triceps brachii and the brachial muscle. The coracoid process serves as an important anchor for several tendinous and ligamentous structures These include, medially to laterally, the tendons of the pectoralis minor, coracobrachialis (CRM), and the short head of the biceps brachii muscles (shBB), and, laterally to medially, the coracohumeral, coracoacromial, coracoclavicular, and superior transverse scapular ligaments. The MCN passes through the CRM and descends between the biceps brachii and brachialis muscles, innervating both of them [1]

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