Nerve transfers in facial palsy

For acute facial nerve repair, best outcomes can be expected when primary tension free nerve coaptation is feasible or nerve grafting when a nerve gap precludes primary neurorrhaphy but a proximal nerve stump exists. When a proximal nerve stump is not available, yet the injury is either acute or subacute (motor end plates are still viable) then nerve transfers are a viable option. By definition, a nerve transfer in the setting of facial palsy means that a nerve in the region of the injured facial nerve is cut distally (preferably a branch, rather than the entire nerve) and transferred and coapted to the proximal distal ends of the cut facial nerve. Thus, the donor nerve is not the facial nerve but rather another nerve. These may be masseter nerve, hemihypoglossal nerve, or spinal accessory nerve. By performing the nerve transfer, an attempt is made at utilizing the intact motor end plates of the target mimetic muscles. This allows axonal growth from the donor nerve and potentially salvaging the mimetic muscles. A caveat is that although function may be achieved utilizing the existing mimetic muscles, spontaneity (or an emotional smile) should not be expected (although may be seen in some individuals) since the donor nerve is not “programed” for emotion but rather other purposes. These include moving the tongue (hypoglossal), chewing (masseter nerve), or raising the shoulder (spinal accessory). Over time, some patients have been reported to develop spontaneity likely to the previously described theory of cortical brain plasticity. In order to attempt overcoming the lack of spontaneity, several cross facial nerve grafts can be added from the contralateral intact facial nerve after accurate mapping of the nerve branches at the time of the nerve transfer. Traditionally these may be coapted to the contralateral facial nerve in an end-to-end fashion after 8-12 months when a positive Tinel sign demonstrates growth to the contralateral side or some authors recently advocate immediate coaptation to the facial nerve distal branches on the paralyzed side. This combination of procedures has been termed “The Baby Sitter Procedure” since the non-facial nerve is maintaining the viability of the neuromuscular units until growth is seen in the cross facial nerve graft and the latter is then coapted to the distal facial nerve branches on the paralyzed side. This “Baby Sitter Procedure” as a whole has been suggested to be more successful if performed in the first 6 months of the injury but has shown inconsistent results in older patients. Still one must recognize that the nerve transfer portion of the surgery is very effective at any age in producing excursion. However, the contribution of the cross facial nerve graft is possibly to add spontaneity. This chapter describes the nerve transfers as a treatment option for facial paralysis, either as a singular procedure or as part of a baby sitter procedure, for patients with facial palsy in the acute or subacute period of up to 12 months, when viable neuromuscular units are still available for recruitment on the paralyzed side.