Nerve to the Zygomaticus Major Muscle for Facial Reanimation Surgery: A Cadaveric Study for Branching Patterns and Axonal Count

BACKGROUND: In facial reanimation surgery, higher donor facial nerve axonal load yields a superior outcome. Nerves supplying the zygomaticus major muscle are primary donors for the grafting procedure; however, their topography has not been studied in detail. This study identified potential donor nerves by quantifying axon loads of the zygomaticus major muscle through histological analysis of cadaveric specimens. MATERIALS AND METHODS: Forty-three hemifaces from 26 fresh human cadavers were studied. Branching patterns of nerves were classified according to their shapes. All branches of interest were sectioned and stained for an axon count. The potential donors were mapped into each tributary of nerves supplying the zygomaticus major. RESULTS: Branching patterns were categorized into five types: Y-type (28%), X-type (28%), H-type (19%), E-type (14%), and F-type (11%). The mean number of axons in the most superiorly and proximally located main branches was 1387.33 ± 406.59 in Y-type, 1021.42 ± 187.79 in X-type, 1222.75 ± 193.82 in H-type, 1496.17 ± 364.567 in E-type, and 1353.40 ± 256.07 in F-type (P > 0.05). A topographic relation between facial nerves supplying the zygomaticus major muscle and their mean axonal load was illustrated. The zygomatic/buccal branches were found within 5 mm from Zuker's point in 100% of X-, Y-, H-, and E-type and 75% of F-type specimens. CONCLUSIONS: Most proximal facial nerve branches supplying the zygomaticus major, arising at the anterior border of a parotid gland, contained over 900 axons in all five branching types. The primary subbranches may be used in selected cases if donor weakness is a concern. Further, our study provides evidence that demonstrates the precision of Zuker's point.