Anatomical study of the masseteric and obturator nerves: application to face transplant and reanimation procedures

Abstract

The masseteric nerve (MN) and the anterior branch of the obturator nerve (ON) that innervate the transferred gracilis muscle have proved highly efficient for reanimating paralyzed facial muscles when muscle transfer is required. Previous researchers have published the total axonal load for myelinated fibers in both nerves. However, the real motor axonal load has not been established. We performed the study on 20 MN and 13 ON. The segments of the MN and the ON were embedded in paraffin, sectioned at 10 μm, and stained following a standard immunohistochemical procedure using anti-choline acetyltransferase to visualize the motor fibers. The MN has a higher axonal load than the ON. There were statistically significant differences between the axonal load of the proximal segment of the MN and the ON. These findings confirm that end-to-end anastomoses between the MN and the ON should preferably use the proximal segment. However, MN neurotomy should ideally be performed between the proximal and distal segments, preserving innervation to the deep fascicles. Our results show that the MN is ideal as a donor motor nerve for reinnervating transplanted muscle for dynamic reanimation of the paralyzed face. The neurotomy should ideally be performed between the first and second collateral branches of the MN.

Conclusion: These findings confirm that end-to-end anastomoses between the MN and the ON should preferably use the proximal and middle segments and the first branch itself and reveal that the MN is ideal as a donor motor nerve for reinnervating transplanted muscle for dynamic reanimation of the paralyzed face. However, the masseteric neurotomy should ideally be performed on the middle segment, preserving the innervation to the deep fascicles.