Radial nerve contribution to brachialis in the UK Caucasian population: Position is predictable based on surface landmarks

The midline of the brachialis muscle is now regarded by many surgeons as an internervous plane, between the musculocutaneous nerve supply to the medial portion and a radial nerve contribution to the lateral portion, a principle applied in anterior approaches to the humerus. The radial nerve to brachialis has been described previously in East Asian specimens (Ip and Chang, 1968, Anat Rec 162:363-371; Mahakkanukrauh and Somsarp, 2002, Clin Anat 15:206-209). We sought to investigate the occurrence and character of this nerve in the UK Caucasian population. Dissection of the musculocutaneous nerve and radial nerve was carried out in Caucasian cadaveric arms (n = 42). The radial nerve was dissected from the spiral groove to the lateral epicondyle. Where a branch to brachialis was encountered, its course and level of origin relative to the length of the arm were noted. The musculocutaneous nerve innervated the brachialis in all specimens. Upon investigation 67% of specimens were found to have a radial nerve branch to brachialis. Sixty-one percent of these branches went straight into the muscle, 13% descended, and 26% recurred. The level of origin of the radial nerve branch to brachialis was at a mean of 23% of the distance between the lateral epicondyle and the acromion (n = 31, range 17-37%, SD = 5.3). In three specimens, two branches were observed. A radial nerve contribution to the innervation of the brachialis was present in 67% of UK Caucasian cadavers, which is less than that noted by others in East Asian specimens. The level of the origin of these branches is predictable based on surface landmarks. This fact may be of use during humeral surgery.