The frontalis muscle is situated across the forehead and is a representative target muscle for botulinum neurotoxin (BoNT) injections aimed at treating horizontal wrinkles in this region. However, a lack of anatomical information regarding the shape and thickness of the frontalis may lead to unexpected adverse effects, such as ptosis and samurai eyebrows, caused by the lack of detail on anatomical variation. Achieving the maximum effect using the minimal amount of BoNT requires a precise injection into the frontalis muscle. The anatomical factors associated with BoNT injection into the frontalis muscle have been reviewed in the current study. Up-to-date understanding of the localization of the BoNT injection point according to an updated understanding of the anatomy leads to more accurate localization of the injection point into the frontalis muscle. Optimal injection sites have been provided for the frontalis muscle, and the injection method has been recommended. The authors suggest optimal injection sites according to the external anatomical landmarks of the forehead. Furthermore, these proposals could aid in a more precise procedure that avoids the deleterious effects of BoNT.
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