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

Figure 3. Dual innervation of a gracilis free muscle transfer achieved by cross-facial nerve graft (coapted distally end-to-end with the
obturator nerve) plus masseteric nerve (coapted proximally end-to-end with the obturator nerve). CFNG: cross-facial nerve graft.

The physiologic basis of dual innervation is still not fully elucidated. Some authors posit that certain nerves
provide greater contributions to spontaneity while others to oral commissure excursion. However,
determining the contribution of individual nerves remains challenging. Furthermore, the effects of
competition between two innervating nerve sources also remain to be understood . Nevertheless, dual
[42]
innervation for GFMT has demonstrated promising results worthy of further investigation. Figures 4 and 5
show preoperative and postoperative photos of two patients who underwent dual innervation GFMT.

OTHER DONOR NERVE OPTIONS
In addition to the trigeminal nerve and CFNG, the SAN and the hypoglossal nerve can also be used to
innervate a GFMT. Because of higher donor nerve morbidity, these are typically reserved for situations
where the options mentioned above are not available. Nerve availability is a particularly important
consideration in patients with Moebius syndrome who often experience several cranial neuropathies. In
patients with Moebius syndrome, 65% have contralateral facial nerve dysfunction, 48% have hypoglossal
nerve dysfunction, and 6% have SAN dysfunction [43,44] . The trigeminal nerve can also be involved;
Cardenas-Mejia et al. found that 7.5% of patients with Moebius syndrome also had an abnormality of the
[45]
trigeminal nerve when assessed with EMG.

In GFMT innervated by SAN, 10 cm of the SAN are dissected and tunneled beneath the platysma muscle to
reach the GFM. The SAN has approximately 1400 axons available for innervation of the muscle
transplant . However, a major disadvantage to using the SAN is donor site morbidity with ipsilateral
[46]
[6]
trapezius weakness and shoulder pain [47,48] . Chuang et al. performed 56 GFMT innervated by the SAN and
found that a majority of patients were able to achieve a full dental display with a smile after 6-12 months.
Forty-five percent of patients achieved a spontaneous smile as measured by a “tickle test”, whereby if a smile
could be elicited directly by tickling, it was classified as spontaneous. This was comparable to their cohort of
patients undergoing GFMT innervated by a CFNG. They also found that SAN innervated GFMT started
moving at approximately 4 months post-operatively and reached optimal results between the first- and