Comparison of static and dynamic symmetry between masseter-innervated and dual-innervated free multivector serratus anterior muscle transfer for complete facial paralysis

Abstract

Purpose: In this study, facial symmetry was compared between the masseter-innervated and dual-innervated free multivector serratus anterior muscle transfer (FMSAMT) methods.

Methods: Eighteen patients with unilateral complete facial paralysis underwent facial reanimation surgery between April 2006 and July 2019. The masseter-innervated FMSAMT group (Group M, n = 8) underwent end-to-end coaptation with the ipsilateral masseter nerve in one stage. The dual-innervated FMSAMT group (Group D, n = 10) underwent end-to-end coaptation with the masseter nerve and end-to-side coaptation with the contralateral facial nerve via cross-face nerve graft. They were further divided into the one-stage (Group D1, n = 5) and two-stage (Group D2, n = 5) subgroups. The durations of periods until the first visible muscle contraction with clenching, first spontaneous smile, and the completion of resting tone were evaluated. The possibility of a spontaneous smile and symmetry of the midline and horizontal deviation at rest and during voluntary smiling were compared between each group.

Results: Groups M and D differed significantly in the possibility of a spontaneous smile and improvement rate of midline deviation and horizontal deviation at rest (p < 0.001, p < 0.001, and p = 0.001, respectively) but not in the improvement rate of midline and horizontal deviation during voluntary smiling. The duration of the period until the completion of resting tone was significantly shorter in Group D1 than in Group D2 (p = 0.048); however, the possibility of a spontaneous smile and the improvement rate of midline and horizontal deviation were not significantly different.

Conclusions: Dual-innervated FMSAMT was effective in guaranteeing a symmetrical resting tone, voluntary smiling, and reproducing a spontaneous smile.

Keywords: Dual-innervation; Facial paralysis; Facial reanimation; Free muscle transfer; Masseter nerve; Serratus anterior muscle.