A bilateral four-headed brachialis muscle with variant innervation: a cadaveric report with possible clinical implications

Abstract

Purpose: Anterior compartment muscles of the arm present high morphological variability, with possible clinical significance. The current cadaveric report aims to describe a bilateral four-headed brachialis muscle (BM) with aberrant innervation. Analysis of the embryological background and possible clinical significance of the BM variant is also provided. Methods: Classical dissection of the upper limb was performed on an 84-year-old donated male cadaver. The cadaver belonged to the Anatomy Department of the National and Kapodistrian University of Athens. Results: On the left upper limb, the four-headed BM was supplied by the musculocutaneous and the median nerves after their interconnection. On the right upper limb, the four-headed BM received its innervation from the median nerve due to the musculocutaneous nerve absence. A bilateral muscular tunnel for the radial nerve passage was identified, between the BM accessory heads and the brachioradialis muscle. Conclusion: BM has clinical significance, due to its proximity to important neurovascular structures and frequent surgeries at the humerus. Hence, knowledge of these variants should keep orthopedic surgeons alert when intervening in this area.