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Page 6 of 14 Gossett et al. Plast Aesthet Res 2021;8:60 https://dx.doi.org/10.20517/2347-9264.2021.69

Figure 2. The sural nerve is a cutaneous sensory nerve providing sensation to the posterolateral leg and lateral foot, heel, and ankle.

Despite the drawback of more limited oral commissure movement, there are reports with the CFNG
resulting in greater postoperative symmetry during smile than other donor nerves. While this may seem to
contradict the data above, symmetry is actually measured separately from oral commissure excursion. The
excursion is typically measured as the distance the oral commissure changes when smiling, whereas
symmetry is measured as the difference in excursion between the healthy side and the operated side.
[18]
Bhama et al. reported that while patients innervated by the CFNG had less excursion when compared to
the masseteric nerve, they experienced better post-operative symmetry by about 1.8 mm. They attributed
this difference to a common neural origin for the zygomaticus major on the unaffected side and the GFMT
on the paralyzed side . Snyder-Warwick et al. assessed 68 GFMT performed in children with an average
[22]
[32]
of 10 years of age and found that both CFNG and masseteric nerve innervation improved symmetry in oral
commissure excursion during a smile. CFNG patients were experiencing an average of 6.5 mm of
improvement in excursion symmetry, whereas the masseteric patients had no significant change in oral
commissure excursion symmetry. However, this finding was likely because the majority of patients treated
with GFMT with masseteric nerve innervation had bilateral facial paralysis, and therefore had less baseline
pre-operative smile asymmetry.

There are differences between outcomes in adults vs. children undergoing GFMT innervated by CFNG,
with children typically achieving better results. This is likely due to the decreased axonal regeneration
achieved in older individuals. A recent study found a relationship between time to achieve Tinel sign in
CFNG and age of the patient, implying a slower rate of nerve regeneration in older patients .
[33]
Hembd et al. examined cadaveric facial nerves and found a significant negative correlation between age
[34]
and axonal load. Numerous other studies conducted in animals and humans have shown axonal
regeneration and total axon counts decrease with age [25,35-37] . Faria et al. found that in 58 patients
[21]
undergoing GFMT innervated by a CFNG, the mean age among patients with excellent or good results was
[38]
significantly lower than in patients with fair or poor results (19.8 years vs. 36.5 years). Terzis et al.
performed 26 GFMT innervated by the CFNG and found that patients younger than 35 had significantly
better results than older patients.