Long-term outcomes of dissection of the depressor labii inferioris muscle to enhance symmetry after free functional gracilis muscle transfer in patients with facial paralysis.

Abstract

In unilateral facial paralysis, overactivity of the contralateral depressor labii inferioris muscle (DLI) often contributes to persistent lower lip asymmetry after free functional gracilis transfer (FFGT). This issue can be addressed through dissection of DLI. We objectively evaluated the long term effects of DLI dissection after FFGT. Patients with unilateral facial paralysis who underwent smile reconstruction with FFGT and subsequent DLI dissection between 2014 and 2023 were retrospectively analyzed. Lower lip height deviation was measured at different time points after DLI dissection. Thirty patients were included with a mean follow-up of 8.41 months. For smiling with exposed teeth, the mean lower lip height deviation significantly decreased from 5.06 mm to 2.58 mm (p < 0.001) following DLI dissection. When first clinical follow-up was conducted within six months, lower lip height deviation was reduced to 2.00 mm (p = 0.0003), follow-ups beyond six months showed a nonsignificant reduction to 3.72 mm. Long-term evaluations revealed initial improvements, followed by a partial regression of results over time (4.83 mm preoperatively, 1.59 mm at 3-7 months [p < 0.01], 3.66 mm at 13-17 months, 2.54 mm at 26-30 months postoperatively). One patient required revision surgery due to a neuroma of the lower lip and two underwent a second DLI dissection. Dissection of the DLI is a safe and effective technique for improving lower lip symmetry after FFGT in the short term. However, the diminishing effect over time highlights the need for patient education about the expected long-term outcomes.