Rare Muscular Variations Identified in a Single Cadaveric Upper Limb: A Four‐headed Biceps Brachii and Coracobrachialis Brevis Muscle Variant

Introduction Supernumerary, or accessory, heads of the biceps brachii are variations associated with the biceps brachii and can vary in number and location in the arm. Variations in other arm muscles, such as the coracobrachialis, can accompany variations in supernumerary biceps brachii musculature. Testut (1899) described two classes of anatomical variations associated with the coracobrachialis muscle: the coracobrachialis longus and coracobrachialis brevis. While they share a common origin at the coracoid process, the coracobrachialis longus and brevis are differentiated by their insertions at the medial epicondyle, and the surgical neck of the humerus, respectively. The objective of this study is to provide a comprehensive description of two rare variant muscles identified in a single cadaveric upper limb: a four‐headed biceps brachii and the tendinous elevator of the latissimus dorsi, a rare coracobrachialis brevis variant. Methods The anatomical variations were identified during routine dissection of the brachial plexus of a left upper limb from an 83‐year old male cadaver. Use of cadaveric material for research purposes was approved by the local research ethics council in the Department of Anatomy & Cell Biology at the University of Western Ontario (REF#: 21082015). Results We observed a four‐headed biceps brachii muscle consisting of both an infero‐medial and infero‐lateral head both originating from the humeral surface. The humeral heads shared a common insertion with the biceps brachii tendon. The tendinous elevator of the latissimus dorsi originated from the coracoid process and inserted on the anterior surface of the latissimus dorsi tendon. A thick fascial structure, considered to be an ancestral remnant of the dorsal epitrochlearis muscle, extended from the latissimus dorsi tendon to the fascia covering the long head of the biceps brachii. Furthermore, an accessory brachialis muscle was also identified in this cadaveric specimen. A variant innervation pattern consisting of a communicating branch between the median and musculocutaneous nerves was also observed. Conclusion These anatomical variations are clinically relevant to surgeons and radiologists as they have potential to compress neurovasculature in the shoulder and arm. Supernumerary heads of the biceps brachii could complicate bone fracture injuries and, subsequent, surgical interventions by causing unusual fracture patterns of the humerus due to their size, orientation and forces produced by these muscles. Furthermore, coracobrachialis brevis variants have been associated with chronic shoulder pain in some individuals. The variants identified here are considered rare, and their co‐occurrence in a single upper limb has not been documented in the literature to our knowledge. Support or Funding Information Supported by NSERC

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.