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Gossett et al. Plast Aesthet Res 2021;8:60 https://dx.doi.org/10.20517/2347-9264.2021.69 Page 3 of 14

Figure 1. Anatomy of gracilis free muscle transfer harvest, demonstrating the neurovascular pedicle consisting of a branch of the
obturator nerve and the adductor artery and vein branches.

found that those innervated by the masseteric nerve had a mean of 2.2 mm greater oral commissure
excursion than those innervated by the contralateral facial nerve (8.7 mm vs. 6.5 mm). Similarly, Bae et al.
[8]
reported a series of 166 children undergoing GFMT and found that oral commissure excursion in
masseteric nerve transfer was 14.2 mm compared to 7.9 mm for CFNG. Manktelow assessed 31 GFMTs
innervated by the masseteric nerve in patients between ages 16 and 61 and found that the commissure on
the reconstructed side moved on average 85% as much as the normal side, with no significant difference
between the two .
[9]

These notable differences in commissure excursion between the masseteric nerve and CFNG may be
[23]
attributed to axonal load. A study by Terzis et al. found that patients with donor nerve axonal counts
greater than 900 had a greater likelihood of achieving good to excellent results. The masseteric nerve has a
shorter distance necessary for axonal growth and requires only a single neurorrhaphy, which leads to a
greater throughput of axons into the obturator nerve of the GFMT. One study comparing donor nerve
histomorphometry via intra-operative nerve biopsies found that the downstream CFNG during the second
2
stage had an average of 1647 axons/mm , 76% less than the distal facial nerve branch biopsied in the first
stage. Another study reported the average number of axons at the distal end of the CFNG to be 453 ± 265 .
[23]
By contrast, the masseteric nerve demonstrated an average of 5289 axons/mm in one study and 2775 ± 470
2
in a separate study [22,24] . When assessed with electromyography (EMG), the masseter muscle itself generates
more contractile force than the muscles of facial expression, and therefore the masseteric nerve may also
provide more robust stimulation than the facial nerve [25,26] .

From a timing perspective, the masseteric nerve offers relatively quick reinnervation and the onset of
[9]
movement of the GFMT [20,21] . Manktelow et al. reported reinnervation in about 3-4 months in his cohort of
[21]
27 patients undergoing GFMT innervated by the masseteric nerve. Faria et al. reported first contractions
observed after 3-6 months, with an average of 3.7 months. This is in contrast to the CFNG, which can take
up to two years for maximal results from the time of initial surgery . Moreover, GFMT with masseteric
[13]
nerve innervation can be done as a single-stage procedure, which is more ideal for patients with significant
medical comorbidities and operative risk. Meanwhile, a CFNG, when done as a two-stage procedure, will