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The brachioradialis muscle (BR) belongs to the lateral forearm muscle. Typically, the radial nerve innervates it. BR morphological variability, such as split muscular belly, split tendon, or accessory BR (ABR), has been described in the current literature. A 68-year-old female donated cadaver was routinely dissected for research and educational purposes. A variant muscle was identified extending at the right arm's lateral and forearm compartments. It originated from the humerus lateral surface between the deltoid and the triceps brachii lateral head, joined the second muscular head from the brachialis muscle, and inserted into the radius styloid process. According to its origin, course, and insertion, the variant muscle probably corresponded to the BR accessory form. However, in the current literature, the ABR morphology corresponds to an accessory muscle originating adjacent to the typical BR and inserted into the radial tuberosity. At the same time, it was defined as "brachioradialis brevis." In the current case, the variant muscle differed significantly from the current literature due to the origin, insertion, length, and relationship with the typical BR; therefore, the term "brachioradialis longus" seemed adequate to describe this variant muscle. [ABSTRACT FROM AUTHOR]

Objective: 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. Methods: 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). Conclusion: 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. [ABSTRACT FROM AUTHOR]