Positional Relationship Between the Orbicularis Oculi and Zygomaticus Complex Muscles by Ultrasonography: New Anatomical Insights for Crow's Feet Injection

The orbicularis oculi muscle (OOc) is strongly associated with facial aging as its contraction causes the formation of crow's feet. Botulinum neurotoxin (BoNT) injection is a representative treatment targeting muscle. The aim of this study was to demonstrate the anatomical relationship between the OOc and the zygomaticus complex muscles, and to visualize the distribution of the facial nerve that innervates the OOc, thereby providing reference data for BoNT injections targeting that muscle. The positional relationships and overlapping ranges between the OOc, zygomaticus minor (Zmi), and zygomaticus major (ZMj), and their distances from the skin, were measured on four different perpendicular planes using ultrasonography. Specimens of the OOc were stained with modified Sihler's stain. The mean distances between the lateral canthus horizontal plane (LCHP) and the zygomaticus complex muscles superior margin were 20.0, 17.9, 22.8, and 20.8 mm in perpendicular planes LC (lateral canthus), OR (orbital rim), M (midpoint of the frontal process of zygomatic bone), and J (Jugale point), respectively. The mean distances between the OOc and the skin were 4.9, 4.8, 5.5, and 4.7 mm in those perpendicular planes. The mean distances between the zygomaticus complex muscles and the OOc were 3.0, 3.1, 4.5, and 4.1 mm. The authors propose new insights for crow's feet injection based on anatomical information obtained from ultrasonography and Sihler's staining, which should contribute to minimizing complications and improving the efficacy of BoNT administration.