Triceps Motor Branch Transfers to the Infraspinatus and Teres Minor Motor Branches for Restoration of Shoulder External Rotation: A Cadaver Study.

BACKGROUND: Recovery of shoulder external rotation after upper brachial plexus injury remains limited. This study investigated the anatomical feasibility of selective neurotizations using radial nerve branches to the triceps brachii as donors for the motor branches to the infraspinatus (bIS) and teres minor (bTm) muscles, aiming to enhance external rotation outcomes. METHODS: Twenty fresh adult cadavers underwent posterior dissections to expose the suprascapular, axillary, and radial nerves. Radial nerve branches to the triceps were identified, measured, and mobilized to simulate transfers to bIS and bTm. Donor-recipient lengths, diameters, and feasibility of coaptation were analyzed. In 10 cadavers, histomorphometric evaluation quantified myelinated axons to assess compatibility. RESULTS: The most frequent branching pattern of the radial nerve included one branch to the long head of the triceps (bLoHT), two branches to the medial head (bMHT1 and bMHT2), and one or two branches to the lateral head (bLaHT1 and bLaHT2). bMHT2 was the longest branch (93.0 ± 8.0 mm, p < 0.05), showed the highest axon count (3646 ± 2333 axons, p < 0.05), and had the best reach to bIS. bLoHT and bMHT2 were the thickest branches (1.99 ± 0.49 mm and 2.07 ± 0.58 mm, respectively; p < 0.05). The most feasible transfers were bMHT2 to bIS and bMHT1 to bTm, both demonstrating 100% feasibility, with diameter and axon count measurements also supporting these neurotizations. CONCLUSIONS: Selective transfers from triceps branches to bIS and bTm are anatomically feasible. Medial head branches combine favorable length, diameter, and axon load, supporting their use as preferred donors to restore external rotation.