Increasing Precision When Targeting the Depressor Anguli Oris Muscle With Neuromodulators: An Ultrasound-Based Investigation

Abstract

Background Neuromodulator treatments of the perioral region are increasingly popular and aim to modulate the position of the modiolus. The predominantly targeted muscle is the depressor anguli oris (DAO) which allows for the modiolus to reposition cranially once temporarily relaxed. Objectives To identify the precise anatomic position of the DAO in relation to the Marionette Line for increasing precision and reducing adverse events during neuromodulator treatments. Methods A total of n = 80 DAO muscles were investigated in n = 40 healthy, toxin naïve volunteers (11 males, 29 females) having a mean age of 48.15 (15) years and a mean body mass index of 24.07 (3.7) kg/m2. The location of the DAO in relation to the labiomandibular sulcus (LMS), its depth, extent, and thickness were investigated with high frequency ultrasound imaging. Results The skin surface projection of the LMS separates the DAO into medial and lateral portions. The distance between skin surface and muscle surface was on average 4.4 mm with males having a greater distance (p < 0.001) and higher BMI being an important influencing factor for a greater distance (p < 0.001). The thickness of the DAO was on average 3.5 mm with a range of 2.8–4.8 mm and with females having thinner muscles when compared to men (p < 0.001). The most favorable injection depth was calculated to be 6.1 mm for intra-muscular product placement. Conclusions Understanding the perioral anatomy and the influence of age, sex, and BMI will potentially allow the injectors to increase efficacy and duration of neuromodulator treatments while expertly managing adverse events.