Achieving Favorable Outcomes in Functioning Free Muscle Transplantation Innervated By Cross Face Nerve Grafts for Smile Reanimation: A Multivariate Regression Analysis of Preoperative Factors
Johnny Chuieng - Yi Lu, MD 1; Jerry Tsung-Kai Lin, MD2; Tommy Nai-Jen Chang, MD3; David Chwei-Chin Chuang, MD1
1Department of Plastic and Reconstructive Surgery, Chang Gung Memorial Hospital, Chang Gung Medical College and Chang Gung University, Taoyuan, Taiwan, 2Department of Surgery, Chang-Gung Memorial Hospital, Linkou Medical Center, Taoyuan, Taiwan, 3Chang Gung Memorial Hospital, Linkou Medical Center, Taoyuan, Taiwan
Cross face nerve graft (CFNG) has traditionally been the choice of donor nerve to innervate functioning free muscle transplantation (FFMT). It offers a more natural, spontaneous smile at a minimal cost of donor site morbidity, but restores adequate symmetric excursion at a slower, more unpredictable, time point. This study aims to investigate critical factors that can predict favorable outcomes when using CFNG.
We performed a retrospective analysis of 43 patients from years 2008 to 2014 who received the two staged CFNG-innervated FFMT. At least 2 years of postoperative follow up was required for inclusion to this study. Patient outcomes were measured using the SMILE evaluation method developed by Hadlock et al. Predictive factors included age, gender, etiology, presence of synkinesis, side of paralysis, onset of paralysis before the first stage, and time between the two stages of FFMT. Univariate analysis of the variables was analyzed by nonparametric Wilcoxon Rank Sum tests and Kruskal-Wallis H tests. Multivariate Linear regression using forced entry method was performed to evaluate the variance of the overall model and the relative potency of each variable.
At an average follow up period of 33 months, the range of excursion ranged from 0.642 to 20.74, with a mean of 10.84. Univariate analysis showed that patients older than 40 years old (p < 0.001), male (p = 0.012), and an etiology other than Bell's palsy (p = 0.008) had significantly higher excursion. In addition, patients with a longer follow up time more than 2 years also had higher correlation with stronger excursion. The linear regression model for multivariate analysis was significant overall (F 4.787, p = 0.001) with R2 of 0.489, and age (standardized beta coefficient 0.379) and gender (standardized beta coefficient 0.308) were the two primary predictors for more favorable outcome.
Donor nerves such as the masseter motor nerve has gradually become the popular choice among surgeons to achieve strong consistent excursion. However, its morbidities in inducing involuntary muscle contractions during mastication can be debilitating and should not be overlooked. CFNG still offers the most spontaneous smile with natural symmetric appearance in young patients that can cooperate with rehabilitation over the long term. With careful selection of patients preoperatively, CFNG can remain a suitable neurotizer for FFMT in smile reanimation.
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