Analysis of the ideal muscle weight of gracilis muscle transplants for facial reanimation surgery with regard to the donor nerve and outcome

Summary Background Free functional muscle transfers represent the ‘criterion standard' for smile reconstruction in facial paralysis. The gracilis muscle is a common donor muscle; however, no data exist regarding the volume of the muscle tissue that is necessary for symmetric commissure excursion. Methods All patients with facial paralysis receiving a free functional muscle transfer for facial reanimation surgery between January 2009 and November 2015 were retrospectively analysed. Only patients with unilateral facial paralysis and documented weight of the muscle portion were included. The extent of oral commissure amplitude was determined from standardised photographs. Results In total, 42 free functional gracilis transfers were performed during the study period, of which 22 met the inclusion criteria. Eight muscles were innervated by a cross-facial nerve graft (CFNG) and 14 by the masseteric nerve. Segments between 19 and 50 g of weight (mean: CFNG, 33.9 g and masseteric nerve, 31.7 g; p = 0.59) were transferred. Coaptation to the masseteric nerve led to increased commissure excursion compared to coaptation to the CFNG. We observed a significant increase in commissure excursion with increasing muscle weight in the masseteric nerve group. In this group, four patients underwent secondary flap debulking in flaps weighing ≥27 g. In the CFNG group, only one patient, who had an initial flap weight of 50 g, underwent secondary flap reduction. Thinning reduced the oral commissure movement but improved the symmetry of commissure excursion and the aesthetic result. Conclusion The ideal muscle weight depends on the donor nerve and should be smaller for masseteric nerve than for CFNG coaptation in adults.