Arm adduction reinnervation utilizing contralateral C7 root in brachial plexus injuries: An anatomical study and case illustration

Background: Brachial plexus injuries (BPI) cause severe upper limb motor and sensory deficits, with functional and psychosocial consequences. In complete BPI, restoration of the thoraco-brachial pinch through arm adduction has rarely been addressed. This study aimed to evaluate the anatomical relationship between the lateral pectoral nerve (LPN) and the contralateral C7 (CC7) root and to assess pectoralis major reinnervation outcomes. Methods: Ten brachial plexuses and 10 LPNs were dissected in five cadavers at the Anatomy Program of McMaster University. The brachial plexus and C7 root were exposed through a supraclavicular approach, and the LPN through an infraclavicular approach. After bilateral identification, a sural nerve graft was tunneled in the presternal subcutaneous plane to measure the distance between them. One patient with total BPI underwent partial CC7 transfer to the LPN using an interposed sural nerve graft. Results: All C7 roots and LPNs were identified in every specimen. The mean distance between the LPN and the CC7 root was 17.5 cm (range, 16.0–19.4). Mean diameters were 4.4 mm (3.9–5.2) for the C7 root and 1.9 mm (1.7–2.2) for the LPN. In the clinical case, the reinnervated pectoralis major achieved a British Medical Research Council grade of 4/5, with no donor-site morbidity. Conclusion: This study demonstrates an accessible, reproducible method for identifying the LPN and supports the anatomical feasibility of CC7 transfer for its reinnervation, providing anatomical and clinical data relevant to reconstructive strategies in complex BPI.