A neuroanatomical analysis of the link between muscle variants and innervation patterns: The accessory head of the biceps brachii muscle as a case example

Anatomical variations of skeletal muscles have been frequently documented in the anatomical literature. Early anatomists, including Albinus, Macalister, and many other researchers of the 18th, 19th, and 20th centuries, conducted detailed studies on muscle morphology and its variability. Contemporary approaches, however, increasingly emphasize the analysis of anatomical variants within the broader context of systems rather than as isolated organs or structures. This report presents a case of an accessory head of the biceps brachii muscle, along with an analysis of the associated neural pattern. The aim is to provide an integrative anatomical description that highlights the interrelationship between muscular and neural variations in the upper limb. During a routine dissection of an isolated left upper limb, a muscular variation of the biceps brachii muscle was observed, consisting of an accessory head. This additional muscular slip was located deep (posterior) to the short head of the biceps brachii and originated from the anteromedial surface of the humeral shaft, just below the insertion of the coracobrachialis muscle. The accessory head of the biceps brachii received its innervation from a slender muscular branch of the musculocutaneous nerve. The biceps brachii is one of the muscles most prone to anatomical variations. Muscular anomalies may correlate with neural variations, either in the course of the nerve or, as in the present case, through additional communicating branches. The clinical relevance of such variations extends beyond altered muscle biomechanics; they should also be considered during surgical procedures, as they may pose a risk of compression of adjacent neurovascular structures. • An accessory head of the biceps brachii was identified during a routine upper limb dissection. • Muscular anomalies may correlate with variations in neural anatomy. • Muscular variants can alter neurovascular topography and potential compression sites. • Muscular and neural variations may coexist, with clinical and surgical implications.