Flap Mass and Outcomes in Gracilis Muscle Transfer for Smile Reanimation
Adeeb Derakhshan, MD1, Diego L Guarin, PhD1, Wenjin Wang, MD, PhD2, Shekhar Gadkaree, MD1, Tessa A Hadlock, MD3 and Nate Jowett, MD3, (1)Harvard Medical School / Massachusetts Eye and Ear, Boston, MA, (2)Shanghai Jiao Tong University School of Medicine, Shanghai, China, (3)Facial Nerve Center - Dept. of Otolaryngology, Harvard Medical School / Massachusetts Eye and Ear, Boston, MA
Background: Gracilis muscle transfer is commonly employed for smile reanimation in facial palsy. Though muscle thinning is thought to reduce the risk of postoperative facial bulk, it carries risk of compromised contraction.
Objectives: To characterize relationships between single-vector gracilis muscle flap mass and degree of post-operative facial bulk, full-effort smile excursion, and resting oral commissure position among patients with unilateral facial palsy.
Methods: Pre- and postoperative images of patients with long-standing facial palsy who underwent free gracilis transfer between 2010 and 2018 and met inclusion criteria (N = 129) were assessed using a machine learning based facial landmark tracking algorithm (Emotrics, Mass Eye and Ear). Linear regression analysis was performed to characterize relationships between flap mass, post-operative facial bulk, smile excursion, and resting oral commissure position. Subgroup analyses were performed for type of facial palsy (flaccid versus postparalytic), age, and neurotization method (nerve-to-masseter, cross-facial, or dual).
Results: In this cohort, 71% of patients had flaccid paralysis. Neurotization was by nerve-to-masseter, cross-facial, or both in 45%, 33%, and 22% of cases respectively. The average gracilis weight was 20.6g (standard deviation = 7.9g, range = 8.6-47.0g). Increasing gracilis muscle mass was correlated with postoperative facial bulk in repose (R = 0.11, p = 0.027). No relationship between muscle mass and excursion was observed for patients with flaccid paralysis, while increasing muscle mass resulted in improved oral commissure excursion among patients with postparalytic facial palsy (p = 0.012).
Conclusion: As flap mass has negligible impact on commissure excursion among patients with flaccid facial palsy, thinning should be employed to reduce the risk of postoperative bulk. In patients with postparalytic facial palsy, sufficient muscle mass should be preserved to maintain the contractile force necessary to overcome the aberrant activity of smile antagonists.
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