Hypoglossal-facial nerve “side”-to-side neurorrhaphy for persistent incomplete facial palsy

Abstract

Object Hypoglossal-facial nerve neurorrhaphy is a widely used method for treating complete facial palsy. However, the classic surgical procedure using a “side”-to-end neurorrhaphy is not suitable for incomplete facial palsy (IFP), because sectioning of the facial nerve for neurorrhaphy compromises remnant axons and potential spontaneous reinnervation. For the treatment of persistent IFP, the authors investigated in rats a modified method using hypoglossal-facial nerve “side”-to-side neurorrhaphy. Methods An IFP model was created by crushing the facial nerve and then ligating the injury site to limit axonal regeneration. After 9 weeks, rats with IFP were submitted to hypoglossal-facial nerve “side”-to-side neurorrhaphy: The gap between the 2 nerves was bridged with a predegenerated peroneal nerve graft, which was sutured to only one-half of the hypoglossal nerve and to the remnant facial nerve through a small window created by removing the epineurium, thus preserving regenerating facial axons. Results Four months after repair surgery, double innervation of the target whisker pad by hypoglossal and facial motor neurons was supported by the recording of muscle action potentials and their retrograde labeling. Regenerated hypoglossal and facial motor neurons effectively participated in the reinnervation of the whisker pad, significantly improving facial symmetry without evident synkinesis, compared with rats that underwent IFP without hypoglossal-facial nerve neurorrhaphy. Conclusions This study demonstrates that hypoglossal-facial nerve “side”-to-side neurorrhaphy with a predegenerated nerve graft can lead to rapid functional benefits for persistent IFP without compromising the remnants of facial axons, thus providing a proof-of-feasibility for further studies in humans.

Electromyography as an intraoperative test to assess the quality of nerve anastomosis – experimental study on rats

“…In two cases, a follow-up EMG after 4 weeks showed nerve conduction. This phenomenon was described previously by other authors who described the ingrowth of nerve fibers in the end-to-side [2,[4][5][6][7][8][9] or the side-toside anastomosis [3,10]. In the aforementioned studies, a nerve sheath was cut at the site before the anastomosis was made to ensure direct contact of nerve fibers between the end and the side of the fused nerves.…”

Protective distal side-to-side neurorrhaphy in proximal nerve injury—an experimental study with rats

“…However, a prerequisite for this technique is the appropriate anatomical structure that allows the approximation of two parallel nerve trunks. For cases not allowing this, various other techniques have been developed to connect parallel nerves to the side-to-side bridge technique with nerve grafts [14, 20, 36] or synthetic conduits [26]. The obvious weaknesses of the present study are the differences in the regeneration capacity as well as the differences of the nerves between rodents and humans.…”

Hypoglossal–facial nerve ‘side’-to-side neurorrhaphy using a predegenerated nerve autograft for facial palsy after removal of acoustic tumours at the cerebellopontine angle

“…In a rat model of persistent incomplete facial paralysis, we have recently demonstrated that rapid reinnervation of the whisker pad can be achieved by the HN–FN ‘side’-to-side neurorrhaphy using an interpositional nerve autograft with preservation of the injured FN 8. Thus, this method may be rapidly performed on patients without compromising the spontaneous reinnervation by the remaining FN axons.…”

“…Most importantly, we used predegenerated nerve grafts (PNG) in our experiments to provide a supportive environment for axonal regeneration. The nerve graft was prepared by sectioning the peroneal nerve and using its distal segment 1 week later 8 9. This procedure is based on the concept that Schwann cells transdifferentiate into repair cells distal to the nerve injury site, thus providing a permissive environment for axon regrowth 10–12.…”