Locational Relationship Between the Lateral Border of the Frontalis Muscle and the Superior Temporal Line

Background: The frontalis is a representative target muscle for botulinum neurotoxin type A injections aimed at treating horizontal wrinkles in the forehead region. However, a lack of information regarding the shape and thickness of the frontalis may lead to unexpected side effects. Methods: This study dissected hemifaces of 44 embalmed Korean and Thai cadavers and performed ultrasound examinations on 20 healthy Korean volunteers. Two anatomical types were identified: (1) the lateral portion of the frontalis covered the superior temporal line (STL) in type I, and (2) the lateral border of the frontalis (LF) and the STL almost coincided in type II. A horizontal line was drawn laterally from the midpoint between the metopion and the glabella while landmarks F1, F2, and F3 were defined as points where this horizontal reference line intersected with vertical lines from the midpoint of the pupil, the lateral canthus, and the lateral orbital rim, respectively. Results: Type I was more common than type II [84% (37/44) vs 16% (7/44)]. When the LF ran along the border, there were no cases in which the STL was not visible. The mean minimum distance in type I was 10.53 mm. The muscle thicknesses at F1, F2, and F3 were 1.80±0.44 mm (mean±SD), 1.61±0.37 mm, and 0.11±0.04 mm, respectively. Conclusions: This study yielded data on the location and thickness of the LF. An anatomical-study-based ultrasound-guided injection technique can achieve reliable results when noninvasive treatment is applied to the forehead area. Financial Disclosure Statement: None of the authors have financial supports from commercial, academic, or political organizations or people regarding this study. The institutional ethics committee approved the study, and the participants provided written informed consents after the study had been fully explained to them (IRB No. 2-2017-0023). Corresponding author: Hee-Jin Kim, DDS, PhD, Room 601, Department of Oral Biology, Yonsei University College of Dentistry, 50-1 Yonsei-ro, Seodaemun-gu, Seoul, 03722, Rep. of Korea, hjk776@yuhs.ac ©2018American Society of Plastic Surgeons

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