Triceps brachii muscle with interconnected accessory heads: A cadaveric case report with implications to the radial, axillary, and ulnar nerves

The triceps brachii muscle is a three-headed muscle in the posterior brachium that chiefly extends the antebrachium. Its neurovascular supply comes from the radial nerve and profunda brachii artery, and its anatomy is intricately associated with the axillary nerve, posterior humeral circumflex artery, and ulnar nerve. While triceps brachii accessory heads (TBAHs) are uncommon, they can impinge contiguous neurovasculature and instigate serious clinical sequelae. The objective of this study is to report a unique case of interconnected TBAHs and discuss its implications to the radial, axillary, and ulnar nerves. Two interconnected TBAHs were discovered during routine dissection of an adult human cadaver. The muscles, their attachments, and the adjacent neurovasculature were cleaned of extraneous fascia and photographed in situ with scale. Literature-based meta-analyses were conducted to situate the variant anatomy within the context of other TBAH cases and convey the associated clinical significances. The 13.79 cm distal accessory head (TBAH dist ) attached to the medial side of the common triceps tendon and converged to a 12.22 cm tendon that coursed over the radial nerve, impeded the axillary nerve in the quadrangular space, and attached to the posteromedial side of the surgical neck of the humerus. The 8.49 cm proximal accessory head (TBAH prox ) exhibited parallel fibers between the triceps brachii medial head and the tendon of TBAH dist , and the TBAH dist tendon displayed a slender tendinous interconnection to the medial epicondyle that confined the ulnar nerve. The interconnection of TBAH dist and TBAH prox distinguishes this case among others and contributes to its clinical relevance. With the ability to provoke concurrent compressive neuropathies of the radial, axillary, and ulnar nerves in three distinctly different anatomical landmark areas, the case holds translational clinical significance. The gross imaging and literature-based meta-analyses from this study may serve as useful resources for clinicians and medical educators deliberating related patient cases. • Review of triceps brachii accessory heads reported in the literature • Description and gross imaging of interconnected triceps brachii accessory heads • Concurrent triceps brachii variations involving three main upper limb nerves • Clinical discussion about neurovascular compression from triceps muscle variations • Clinical narrative about radial, axillary, and ulnar neuropathies