Ji Zhang; Xing jiao Ma; Fei Xu & Sheng bo Yang
The precise targets of botulinum toxin type A (BoNT-A) for the treatment of hemifacial spasm (HFS) and facial-cervical wrinkle reduction remain unclear. This study aimed to elucidate the location and area of the intramuscular nerve dense region (INDR) in each mimetic muscle innervated by the facial nerve, and to use them as precise targets for BoNT-A injection. Mimetic muscles obtained from 12 formalin-fixed adult Chinese cadavers (male:female = 1:1) were subjected to modified Sihler’s staining to demonstrate the whole-mount intramuscular nerve branching distribution pattern. The location and area of the INDRs were measured and identified for each muscle. The locations of the INDRs varied among the mimetic muscles: medial part of the middle muscle belly for the frontal belly of the occipitofrontalis; middle part of the upper and lower eyelids and lateral canthus level for the orbicularis oculi; middle muscle belly for the zygomaticus major, levator labii superioris, risorius, depressor anguli oris, depressor labii inferioris, and mentalis; middle- lower muscle belly for the zygomaticus minor; junction of the middle and upper thirds for the nasalis; junction of the middle and lower thirds for the levator labii superioris alaeque nasi; for the orbicularis oris, upper part at the midpoint of the oral commissure-philtrum line and lower part just below the oral commissure; and upper muscle belly for the platysma. The area of the INDR in the above-mentioned mimetic muscles varied in size, but no statistically significant differences were observed between the left and right sides or between males and females (P > 0.05). The delineation of the location and area of these INDRs can provide guidance for targeted BoNT-A injection, thereby ensuring therapeutic efficacy while reducing the risk of complications.
KEY WORDS: Mimetic muscles; Intramuscular nerve; Sihler’s staining; Botulinum toxin A; Target localization.
ZHANG, J.; MA, X. J.; XU, F. & YANG, S. B. Intramuscular nerve distribution in mimetic muscles: An anatomical study to guide BoNT-A injection. Int. J. Morphol., 44(4):1122-1128, 2026.
