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: The aim of this study was to identify the precise anatomic position of the DAO in relation to the marionette line, thereby 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) with a mean [standard deviation] age of 48.15 [15] years and a mean BMI of 24.07 [3.7] kg/m2. The location of the DAO in relation to the labiomandibular sulcus, and its depth, extent, and thickness were investigated with high-frequency ultrasound imaging.

Results: The skin surface projection of the labiomandibular sulcus 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 < .001) and higher BMI being an important influencing factor for a greater distance (P < .001). The thickness of the DAO was on average 3.5 mm, with a range of 2.8 to 4.8 mm and with females having thinner muscles compared with males (P < .001). The most favorable injection depth was calculated to be 6.1 mm for intramuscular product placement.

Conclusions: Understanding the perioral anatomy and the influence of age, sex, and BMI will potentially allow injectors to increase the efficacy and duration of neuromodulator treatments while expertly managing adverse events.