American Society for Peripheral Nerve

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Cervical Branch Nerve Transfer for Restoring Marginal Mandibular Nerve Function
Andres Rodriguez, MD, PhD1; David Jensson, MD1; Wolfgang J. Weninger, MD2; Stefan Meng, MD2; Chieh-Han John Tzou, MD, PhD2
1Uppsala University Hospital, Uppsala, Sweden, 2Medical University Vienna, , Vienna, Austria

Background: Injuries of the marginal mandibular branch (MM) of the facial nerve results in paralysis of lower lip muscle depressors and asymmetrical smile. Nerve reconstruction when possible is the method of choice, however in the presence of long nerve gaps or delayed nerve reconstruction, conventional nerve repairs maybe difficult to perform or provide suboptimal outcomes. Herein we investigate the anatomical technical feasibility of the nerve transfer of the cervical branch of the facial nerve (CB) to the MM for restoration of lower lip function. In addition we present a clinical case where this nerve transfer was successfully performed.

Methods: Ten adult fresh cadavers were dissected. Measurements included the number of MM and CB branches, maximal length of dissection of the CB from the parotid and the distance from anterior border of parotid to the facial artery. CB reach for direct coaptation to the MM at the level of the crossing with the facial artery was assessed. We also performed histomorphometric analysis of the MM and CB branches. We present a clinical case of a 66 years-old man with a soft tissue sarcoma in the face that needed resection of skin, submandibular gland and sacrifice of the MM, reconstructed with CB to MM nerve transfer and a free flap for soft tissue coverage.

Results: The anatomy of the MM and CB was consistent in all dissections, with an average number of sub branches of 1.5 for the MM and 1.2 for the CB. The average maximal length of dissection of the CB was of 46.5 mm and in every case tension-free coaptation with the MM was possible at the level of crossing with the facial artery. The histomorphometric analysis demonstrated that the MM nerve contained an average of 3856 myelinated fiber counts per mm and of 5015 for the CB . After 3-years follow-up of the clinical case, complete recovery of MM function was observed without need of central relearning and without functional or aesthetic impairment resulting from the denervation of the platysma muscle.

Conclusion: The CB to the MM nerve transfer is an anatomically feasible procedure for reconstruction of isolated MM nerve injuries being a valid alternative to conventional nerve grafts. In our patient, by direct nerve coaptation fully recovery of lower lip muscle depressors was achieved without the need of central relearning due to the synergistic functions of the CB and MM functions and with minimal donor site morbidity.

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