Restoring the spontaneous smile through free functional muscle transfer. A systematic review and meta-analysis of the last twenty years’ experience

Abstract

The recovery of the spontaneous smile has become a primary focus in facial reanimation surgery and its major determinant is the selected neurotizer. We aimed to compare the spontaneity outcomes of the most preferred neurotization methods in free functional muscle transfer for long-standing facial paralysis. The Embase, Ovid Medline, and PubMed databases were queried with 21 keywords. All clinical studies from the last 20 years reporting the postoperative spontaneity rate for specified neurotization strategies [cross-face nerve graft (CFNG), contralateral facial nerve (CLFN), motor nerve to the masseter (MNM), and dual innervation (DI)] were included. A meta-analysis of prevalence was performed using Freeman-Tukey double arcsine transformation, I2 statistic, and generic inverse variance with a random-effects model. Risk Of Bias In Non-randomized Studies of Interventions and Newcastle-Ottawa scale were used to assess bias and study quality. The literature search produced 2613 results and 473 unique citations for facial reanimation. Twenty-nine studies including 2046 patients were included in the systematic review. A meta-analysis of eligible data (1952 observations from 23 studies) showed statistically significant differences between the groups (CFNG: 0.94; 95% confidence interval [CI], 0.76-1.00, CLFN: 0.91; 95% CI, 0.49-1.00, MNM: 0.26; 95% CI, 0.05-0.54, DI: 0.98; 95% CI, 0.90-1.00, P<0.001). In pairwise comparisons, statistically significant differences were found between MNM and other neurotization strategies (P<0.001 in CFNG compared with MNM, P=0.013 for CLFN compared with MNM, P<0.001 for DI compared with MNM). DI- and CLFN-driven strategies achieved the most promising outcomes, whereas MNM showed the potential to elicit spontaneous smile at a lower extent. Our meta-analysis was limited primarily by incongruency between spontaneity assessment systems. Consensus on a standardized tool would enable more effective comparisons of the outcomes.