Double powered free gracilis muscle transfer for smile reanimation: a longitudinal optoelectronic study

The choice of the motor donor nerve is a crucial point for free flap transfer algorithms. In case of unilateral facial paralysis, the contralateral healthy facial nerve can provide coordinated smile animation and spontaneous emotional expression, but with unpredictable axonal ingrowth into the recipient muscle. Otherwise, the masseteric nerve ipsilateral to the paralysis can provide a powerful neural input, without a spontaneous trigger of the smile. Harvesting a bulky muscular free-flap may enhance quantity of contraction but esthetic results are unpleasant. So, the logical solution to obtain high amplitude of smiling combined with the spontaneity of movement is to couple neural input: the contralateral facial nerve plus the ipsilateral masseteric nerve. Thirteen patients with unilateral dense facial paralysis underwent a one-stage facial reanimation with a gracilis flap powered by a double donor neural input, provided by both the ipsilateral masseteric nerve (coaptation by an end-to-end neurorrhaphy with the obturator nerve) and the contralateral facial nerve (coaptation through a cross-face nerve graft: end-to-end neurorrhapy on the healthy side and end-to-side neurorrhaphy on the obturator nerve, distal to the masseteric/obturator neurorrhaphy). Their facial movements were evaluated with an optoelectronic motion analyzer. Before surgery, on average the paretic side had a total three-dimensional mobility smaller than the healthy side, with a 52% activation ratio and more than 30% of asymmetry. After surgery, the differences significantly decreased (ANOVA, p<0.05), with an activation ratio between 75% (maximum smile) and 91% (maximum smile with teeth clenching), and less than 20% of asymmetry. Similar modifications were seen for the performance of spontaneous smiles. The significant pre-surgical asymmetry of labial movements reduced after surgery. The use of a double donor neural input permitted both movements that were of force similar to that of the healthy side, and spontaneous movements elicited by emotional triggering.