Supernumerary Head of the Biceps Brachii Muscle: An Anatomic Variant With Clinical Implications

Abstract

Objective: The purpose of this anatomic case report is to describe a variation of the biceps brachii muscle identified in an adult male cadaveric specimen and its potential clinical relevance.

Methods: A cadaveric specimen with a left supernumerary biceps brachii muscle was dissected. Adjacent neurovascular structures were isolated, and their pathways were observed for possible areas of compression.

Results: A tricipital supernumerary head of the biceps brachii muscle was noted on the left upper extremity in an embalmed human cadaveric specimen. The median nerve and brachial artery maintained their common neurovascular path. The musculocutaneous nerve passed deep to the third head of the anatomic variant before distributing its cutaneous branches as the lateral antebrachial cutaneous nerve.

Conclusion: The presence of a supernumerary biceps brachii muscle may cause neurovascular compression of the median nerve, musculocutaneous nerve, or brachial artery, resulting in peripheral nerve deficits. When patient conditions are refractory to care, they may warrant careful evaluation of the anterior compartment of the arm for potential anomalous muscle variations.

Keywords: Anatomic Variation; Forearm; Median Nerve; Musculocutaneous Nerve.

Fig 1

Photo and illustration of dissection demonstrating the long head (A), short head (B), and supernumerary head (C) of the biceps brachii muscle. Illustration by Christina Pecora.

Fig 2

Illustration of a 3-headed biceps brachii muscle demonstrating the long head (A), short head (B), and supernumerary head (C). The musculocutaneous nerve (yellow), with its lateral antebrachial branches of the forearm, and the median nerve (purple) are common sites for neurovascular compromise. The single black arrowhead signifies where the musculocutaneous nerve passed deep to the tendon of the supernumerary biceps tendon. This may be a site of compression, as typically this nerve passes in the middle to distal third of the brachium. The common insertion point of the brachialis and biceps brachii is shown at the asterisk (*). Illustration by Frank Scali; used with permission.