INTRODUCTION
The discovery of the aesthetic applications of botulinum neurotoxin type A (BoNTA) was a revolutionary change in aesthetic medical practice, providing a less invasive approach to facial rejuvenation and sculpting to achieve a more youthful appearance.1 Three BoNTA products are available for aesthetic use in the US: abobotulinumtoxinA (Dysport®, Medicis
Aesthetics Inc., Scottsdale, AZ),2 incobotulinumtoxinA (Xeomin
®, Merz Pharmaceuticals, LLC, Greensboro, NC),3 and onabotulinumtoxinA
(Botox® Cosmetic, Allergan, Inc., Irvine, CA)4
(Table 1). Doses of different BoNTA products are not interchangeable,
or even directly comparable, due to differences in production
and assay methods3,5,6; however, the techniques for treatment
are otherwise generally similar. Although these products are widely used in aesthetic treatment of different facial areas, most research has focused on the temporary improvement of glabellar lines, for which multiple clinical studies have shown that BoNTA injections are effective and well tolerated.7-16
Achieving the desired outcome with BoNTA while minimizing the risk for adverse events requires proper dosing and accurate placement
of injections to avoid migration of the product outside the target muscle. An optimal treatment plan takes into account facial anatomy, the interactions of adjacent muscle groups, and muscle mass. The muscles underlying the glabella are, in most patients, among the larger targets for BoNTA treatment of the face and require higher doses than most other facial muscles commonly treated with BoNTA.17 Furthermore, each of the muscles of the glabellar
complex varies in mass and strength among individuals. Anatomic diagrams and bony landmarks such as the bony orbital ridge form an inadequate basis for placement of the injections; dynamic evaluation of the glabellar muscles via visualization and palpation at rest and at maximal contraction is needed to assess their location, bulk, contour, and symmetry.17 Clinical trials have typically evaluated standardized doses of BoNTA and a fixed number
of injection sites for the treatment of glabellar lines. Formal grading scales for muscle mass may improve comparability of trial data and also find clinical applications.
This review will focus on the nuances of technique, including the need to judge muscle mass in individual patients and adjust dose based on muscle mass, when using BoNTA to treat glabellar lines.
Considerations for Optimal Treatment of Glabellar Lines
Muscular Anatomy of the Glabellar Complex
Muscles of the glabellar complex responsible for the formation of frown lines include the corrugator supercilii, depressor supercilii, procerus, and orbicularis oculi para frontalis muscles (Figure 1). The corrugator supercilii lies below the frontalis muscle and functions to draw the brow medially and downward, whereas the smaller depressor supercilii is located lower than the corrugator muscle and functions to draw the medial brow downward. The procerus is located between the eyebrows and also works to depress the glabellar medial brow region. The depressor function of the glabellar complex is opposed by the frontalis muscle. This muscle is merged with the superior portions of the glabellar complex, from which it extends upwards underneath the forehead. The frontalis is the sole brow elevator.17 Understanding of the anatomic location and interplay between elevator and depressor muscles is needed to guide injection technique in order to achieve a smooth, balanced, and aesthetically pleasing outcome with BoNTA.
Muscles of the glabellar complex responsible for the formation of frown lines include the corrugator supercilii, depressor supercilii, procerus, and orbicularis oculi para frontalis muscles (Figure 1). The corrugator supercilii lies below the frontalis muscle and functions to draw the brow medially and downward, whereas the smaller depressor supercilii is located lower than the corrugator muscle and functions to draw the medial brow downward. The procerus is located between the eyebrows and also works to depress the glabellar medial brow region. The depressor function of the glabellar complex is opposed by the frontalis muscle. This muscle is merged with the superior portions of the glabellar complex, from which it extends upwards underneath the forehead. The frontalis is the sole brow elevator.17 Understanding of the anatomic location and interplay between elevator and depressor muscles is needed to guide injection technique in order to achieve a smooth, balanced, and aesthetically pleasing outcome with BoNTA.
The facial musculature of the individual patient (Figures 2 and 3) critically affects treatment decisions for several reasons. Gender-based differences may influence treatment decisions, and, in
