Increasing precision during neuromodulator injections for frontal rhytids-Using ultrasound imaging to identify the line of convergence

Abstract

Background: Recent research introduced the concept of the "line of convergence" as a guide for injectors to enhance precision and avoid complications when treating the frontalis muscle with toxins. However, currently, no pre-injection ultrasound scanning is employed to increase precision and reduce adverse events when searching for the line of convergence.

Objective: To explore the feasibility and practicality of implementing pre-injection ultrasound scanning into aesthetic neuromodulator treatments of the forehead.

Methods: The sample of this study consisted of n = 55 volunteers (42 females and 13 males), with a mean age of 42.24 (10.3) years and a mean BMI of 25.07 (4.0) kg/m². High-frequency ultrasound imaging was utilized to measure the thickness, length, and contractility of the frontal soft tissue and to determine the precise location of the line of convergence during maximal frontalis muscle contraction.

Results: The results revealed that the line of convergence was located at 58.43% (8.7) of the total forehead height above the superior border of the eyebrow cilia without a statistically significant difference between sex, age, or BMI. With frontalis muscle contraction, the forehead shortens in males by 25.90% (6.5), whereas in females it shortens only by 21.74% (5.1), with p < 0.001 for sex differences.

Conclusion: This study demonstrated the feasibility and practicality of pre-injection ultrasound scanning for facial aesthetic neuromodulator treatments. Knowing the location of the line of convergence, injectors can determine precisely and on an individual basis where to administer the neuromodulator deep or superficial or when the injection location is at risk to cause eyebrow ptosis.

Keywords: facial anatomy; forehead; line of convergence; neuromodulator injections; ultrasound.