Background: Free functional muscle transfer has become a common treatment modality for smile restoration in long-lasting facial paralysis, but the selection of surgical strategy between a 1-stage and a 2-stage procedure has remained a matter of debate. The aim of this study was to compare the quantitative and qualitative outcomes of smile excursion between 1-stage and 2-stage free muscle transfers in the literature. Methods: A comprehensive review of the published literature between 1975 and end of January 2017 was conducted. Results: The abstracts or titles of 2, 743 articles were screened. A total of 24 articles met our inclusion criteria of performing a quantitative or qualitative evaluation of a free-functioning muscle transfer for smile restoration. For the purpose of meta-analysis, 7 articles providing quantitative data on a total of 254 patients were included. When comparing muscle excursion between 1-stage and 2-stage procedures, the average range of smile excursion was 11.5 mm versus 6.6 mm, respectively. For the purpose of systematic review, 17 articles were included. The result of the systematic review suggested a tendency toward superior functional results for the 1-stage procedure when comparing the quality of smile. Conclusions: The results of this review must be interpreted with great caution. Quantitative analysis suggests that 1-stage procedures produce better excursion than 2-stage procedures. Qualitative analysis suggests that 1-stage procedures might also produce superior results when based on excursion and symmetry alone, but these comparisons do not include one important variable dictating the quality of a smile - the spontaneity of the smile. The difficulty in comparing published results calls for a consensus classification system for facial palsy.
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