Background: Triceps function as an elbow extensor and stabilizer is an increasingly recognized goal of brachial plexus reconstruction. Intercostal nerve transfer to the triceps brachii is employed to this end, especially in double-free muscle transfer. However, the particular triceps branch to which intercostals are coapted has not been characterized and the anatomy of the triceps branches relevant to nerve transfers has not been described.

Methods: The anatomy of nerves innervating the triceps brachii was defined in ten cadaveric limbs to evaluate these motor branches as recipients in intercostal nerve transfers. Length, diameter, and branching patterns of triceps motor branches as well as their location relative to relevant anatomic landmarks were recorded. Intercostal nerve transfers (T3 and T4) to triceps branches were simulated.

Results: Only two triceps branches consistently originated in the axilla, allowing relatively simple exposure via the anterior or axillary approach – long head nerve and ulnar collateral nerve. The long head nerve was the most proximal branch of the radial nerve and provided the sole innervation to the long head in all but one specimen. On average, the long head nerve had a diameter of 1.2 mm and traveled 76 mm before penetrating the long head. The ulnar collateral nerve originated from the radial nerve 12.2 mm distal to the origin of the long head nerve, had a diameter of 0.9 mm and traveled 100 mm before penetrating the medial head. Direct intercostal nerve transfer to the long head nerve and ulnar collateral nerve was anatomically feasible in all specimens.

Discussion: Anatomically, the long head nerve is the preferred recipient for intercostal nerve transfer for several reasons. First, this branch is most accessible at surgery either through a deltopectoral or axillary incision. Second, as the shortest of triceps branches, nerve transfer to the long head nerve would minimize muscle denervation time. Third, the long head nerve is the sole source of innervation to its head, while the ulnar collateral nerve supplies only part of the medial head (along with the nerve to the anconeous/medial head). Fourth, the cross-sectional area of the long head nerve is greater than the ulnar collateral nerve. Fifth, recovery of long head action as an arm adductor would potentially stabilize the shoulder.

Conclusions: This study confirms the anatomic feasibility of direct intercostal nerve transfer to the long head nerve and demonstrates anatomic factors that make it the superior triceps branch recipient in nerve transfers.