Effect of Distal Masseter to Facial Nerve Transfer in Paralytic Patients with Preserved Facial Nerve Continuity on Improving Scaled Measurement of Improvement in Lip Excursion (SMILE): A Vectoral Analysis

Abstract

Objective: Distal masseter-to-facial neurorrhaphy is an option to improve smile excursion in facial paralysis patients in the early period without truncating the facial nerve truncus and by ensuring the continuity of the facial nerve. This study aimed to study the effect of distal masseter-to-facial neurorrhaphy on smile excursion.

Methods: Charts of eight patients were retrospectively examined. Screenshots showing the best possible smiles were taken from preoperative videos. Screenshots were taken from postoperative videos showing the best combination of a natural smile on the healthy side and a smile with clenched teeth on the paralytic side. Emotrics and Photoshop software were used for computing vertical, horizontal, and overall excursion from facial landmarks. Scaled measurements of improvement in lip excursion and lip angle was evaluated. Symmetry was evaluated by accepting the healthy side as 100 percent, and the paralytic side was calculated as a percentage of the healthy side.

Results: Five patients had total facial paralysis and three had facial paresis. Mean postoperative follow-up period was 15.0 +/- 10.2 months. The average interval between facial denervation and nerve repair was 14.0 +/- 4.1 months (range, 11-23). All neurorrhaphies were coapted end-to-end to either the zygomatic or the buccal branch without an interposition graft. Mean postoperative initial movement occurred at 95.5 +/- 20.5 days (range, 72-138). Paralytic side to healthy side horizontal excursion changed from preoperative 72.5 +/- 17.4% to postoperative 93.4 +/- 6.9%. Vertical excursion changed from preoperative 38.4 +/- 24.6% to postoperative 89.3 +/- 11.8%. Overall excursion changed from preoperative 68.4 +/- 19.6% to postoperative 92.9 +/- 10.4%. Paralytic side to healthy side mean lip angle changed from 64.7% preoperative to 95.2% postoperatively. All changes were statistically significant (p<0.05).

Conclusion: Facial paralysis patients with an asymmetric smile benefit from distal masseter-to-facial nerve transfer and it improves smile excursion dramatically. This effect was especially prominent in the vertical component of the smiling vector.