Incidence of accessory brachialis muscle, variations in its insertion and relation with surrounding neurovascular structures

Background. Accessory brachialis (AcBr) muscle can compromise the surrounding neurovascular structures due its variable insertion. In this context, the objective of the present study was to determine the incidence of AcBr muscle, variation of its insertion and relation with surrounding neurovascular structures. Methods. The study was performed in 84 formalin fixed human cadaveric upper limb specimens, which were available in the department of anatomy. The insertion pattern of the AcBr muscle was divided into 5 types (type 1, type 2, type 3a, type 3b and type 4). Results. It was observed that, AcBr muscle was present in 46 (54.8%) cases. In 31 cases (67.4%), this muscle inserted into the main tendon of brachialis muscle (type 1). It joined the tendon of biceps brachii (type 2) in 6 cases (13%). In 7 cases (15.2%), it gave a slip which joined the supinator muscle after passing deep to the radial recurrent vessels (type 3a). In a single case (2.2%), the slip merged with the supinator after passing superficial to the radial recurrent vessels (type 3b). In one case (2.2%), it gave muscular fibres which crossed the radial nerve and merged with the brachioradialis muscle (type 4). Conclusions. The present study observed higher frequency of incidence of AcBr muscle, however, the limitation of this study is that the small number of specimens studied. The findings will be more accurate with a larger sample size. The gender-based comparison was not performed, since the study involved disarticulated upper extremities.