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Gossett et al. Plast Aesthet Res 2021;8:60 https://dx.doi.org/10.20517/2347-9264.2021.69 Page 7 of 14

COMBINATION OF DONOR NERVES
Dual-innervation for GFMT is a promising avenue for the future of dynamic smile reanimation, potentially
taking advantage of the strengths of different donor nerve sources while also compensating for their
weaknesses. The most common combination of dual-innervation is the use of the masseteric nerve plus
CFNG [Figure 3], which could provide increased excursion from the masseteric nerve and spontaneity from
[16]
the CFNG . However, while dual-innervation continues to gain popularity, it also remains difficult to
determine the success of each donor nerve in innervating the GFMT.

[39]
In 2009, Watanabe et al. first described providing dual innervation of a free latissimus dorsi muscle
transfer using the masseteric nerve and a CFNG, with evidence of dual innervation on EMG in three
[16]
patients. Several years later, Biglioli et al. then described this same technique of dual innervation in four
patients using the GFMT instead of the latissimus dorsi muscle. This was performed in a single-stage
procedure, where the masseteric nerve was coapted to the obturator nerve in an end-to-end fashion while
the CFNG was coapted via an epineural window (without transecting axons) distal to the masseteric nerve
coaptation. Although this was a small cohort, all four patients were able to achieve good smile results.

[15]
Cardenas-Mejia et al. performed GFMT dually innervated by the masseteric nerve and CFNG in 9 adult
patients utilizing a two-stage technique for the CFNG. This was done with an end-to-end coaptation
between the CFNG and the distal end of the obturator nerve. The masseteric nerve was connected more
proximally 1 cm distal to the gracilis muscle. In the study, all patients recovered voluntary and spontaneous
smile abilities at an average of 8.8 weeks as measured by pre- and post-operative videos analyzed by the
surgeon . Mcneely et al. assessed 9 children (mean age 8.6) who underwent a two-stage GFMT also
[40]
[15]
innervated by the CFNG and masseteric nerve, both of which were coapted to the obturator nerve in an
end-to-end fashion. They noted that all patients achieved spontaneous smiles 3 to 7 months after GFMT,
assessed by the surgeon at follow-up. The average time between stages was 13.3 months. Another study by
Sforza et al. of 13 patients who underwent a single-stage GFMT dually innervated with masseteric nerve
[41]
(end-to-end) and CFNG (end-to-side epineural window, distal to masseteric nerve coaptation) reported
that 70% of patients achieved spontaneous smile at 1-2 years post-operatively. In the study 15% of patients
did not achieve any smile reanimation. The authors did not specify if failures were due to axonal ingrowth
disturbance or microvascular impairments.

There is currently limited data comparing single-stage and two-stage CFNG during dual innervation
GFMT. However, two-stage surgery ensures that the distal ends of both the masseteric nerve and CFNG
have viable axons when coaptation to the GFMT. Theoretically, this would allow for more synchronous
innervation of motor units in the GFMT from both sources. However, if single-stage surgery is found to
achieve comparable outcomes, it would obviate the need for multiple operations and potentially allow
patients to enjoy the restoration of smiles sooner. Dusseldorp et al. reported a retrospective case-control
[14]
study comparing spontaneity in 24 single-stage innervation GFMT with either CFNG or masseteric nerve
alone vs. 25 dually innervated (CFNG plus masseteric nerve) GFMT. Dual innervation was achieved either
through an interfascicular split, y-shaped neurorrhaphy, or a proximal epineural window end-to-side CFNG
coaptation and a distal end-to-end masseteric coaptation. Spontaneity was measured using the previously
described SSA, and the authors found that spontaneity in dually innervated patients (33%) was superior to
that of the masseter alone patients (20%) but inferior to that of the CFNG alone patients (75%), although
there was no statistically significant difference detected between groups. Interestingly, there were also no
significant differences in oral commissure excursion or eFACE scores between groups.