An Anatomical Feasibility Study on the Use of the Hypoglossal and Hemi–Hypoglossal Nerve as a Donor Motor Nerve for Free Functioning Muscle Transfer in Upper Extremity Reconstruction

Abstract

Objective/Hypothesis: Reconstruction of adult brachial plexus injuries remains a clinical challenge. The advent of nerve transfers and free functioning muscle transfers has increased the available reconstructive options in particular when there have been root avulsions. The accessory, intercostals, and phrenic nerves have been the most common donor nerves used to reanimate free muscle transfers. However, it is not uncommon for these patients to have sustained multiple rib fractures or a phrenic nerve avulsion precluding the use of either nerve as a donor. The paucity of currently available donor motor nerves for transfer led us to investigate the hypoglossal and hemi–hypoglossal nerve as a potential donor nerve for a free functioning muscle transfer. The hypoglossal and hemi–hypoglossal nerve have been used successfully as a nerve transfer for the facial nerve and with some success as a nerve transfer with nerve grafts to the musculocutaneous nerve in obstetrical brachial plexus palsy. We postulated that the hypoglossal and hemi–hypoglossal nerve could be used for nerve transfer without nerve grafts for innervation of a gracilis or latissimus dorsi muscle for elbow flexion in upper extremity reconstruction. To our knowledge, this has not been studied before. Materials and Methods: In 12 formalin-embalmed cadavers (6 males and 6 females), the hypoglossal, thoracodorsal, and obturator nerve branch to gracilis was dissected bilaterally and their respective lengths from their origin to the muscle measured. The distance from the lowest point of the hypoglossal nerve in the neck to the lateral third of the clavicle was measured. Results: The average distance from the lowest point of the hypoglossal to the lateral clavicle was 8.4 ± 1.3 cm in males and 7.7 ± 0.8 cm in females. When the hypoglossal was transected distally and brought down, the average distance to the clavicle was 4.5 ± 1.6 cm in males and 3.8 ± 1.5 cm in females. The average length of the nerve to the gracilis was 13.1 ± 1.6 cm in males and 12.4 ± 11 cm in females and of the thoracodorsal nerve 14.9 ± 1.5 cm in males and 14.0 ± 1.0 cm in females. Conclusion: This cadaveric study demonstrates that the hypoglossal and hemi–hypoglossal nerves may be used as potential motor donor nerves by direct nerve transfer without the need for nerve grafting to innervate a free functioning gracilis or latissimus dorsi muscle for upper extremity reconstruction.