The accessory brachioradialis muscle (brachioradialis accessorius): Prevalence of a rare variant with possible implications for radial nerve compression

Abstract Purpose The brachioradialis muscle (BR) belongs to the radial forearm muscles and contributes to the elbow flexion. Accessory brachioradialis muscle (ABR) or brachioradialis “accessorius” represents an uncommon BR variant, not been enough studied. The present study investigates the incidence of the ABR variant, along with its origin, insertion, and innervation. Materials: Eighty-three (83) upper limbs were meticulously dissected at the arm, forearm, and cubital fossa to investigate the ABR presence. When the variant muscle was identified, morphometric measurements were obtained. Results The ABR was identified in two upper limbs (2/83, 2.4%), in a male cadaver, bilaterally. Its origin was located along with the typical BR, and its insertion was identified into the anterior surface of the radius. The radial nerve supplied the ABR, having a course posteriorly to it (in a deeper layer). Conclusions In the current study, the variant muscle was observed in 2.4%, while the ABR reported incidence is recorded between 0.5–2.8%. Radial nerve compression, at the forearm, is not an uncommon entrapment neuropathy. The relationship between the radial nerve and the ABR could precipitate radial neuropathy.