Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Treatment of frontalis and horizontal forehead lines with neuromodulators
Summary and key features
-
Frontalis muscle properties (force, height, and length) influence neuromodulator treatment.
-
When performing neuromodulator treatment of the frontalis muscle, priority should be placed on brow height over brow shape.
-
Neuromodulator injection grid maps providing a “guide” for treating all patients should be avoided in routine clinical practice.
Introduction
The brow, defined here as the intersection of the forehead and upper eyelids, is the core of facial expression. Frontalis, the only elevator of the brow, convenes with the corrugators, procerus, and other depressors of the brow to form movements that serve as important social and emotional signals. Darwin even wrote in 1872 of the “omega melancholia” between the eyebrows as a sign of depression. Eyebrows and their position, determined in large part by frontalis movement, are not only appreciated by others from a considerable physical distance but also essential for the recognition of an individual. The horizontal lines that form frontalis contraction are often a chief concern among cosmetic patients. The treatment of horizontal forehead lines with botulinum toxin A, though seemingly straightforward, in fact requires the injector to balance competing goals of line reduction with maintenance of brow position and a “natural”–appearing outcome. This is all the more important in the setting of the COVID-19 pandemic and increased use of facial coverings, which have renewed attention to forehead and brow expression. Moreover, recent research has updated our understanding of frontalis muscle structure, patterns, and motion. This chapter will review this information and focus on optimizing neuromodulator treatment and outcomes.
Anatomy
Pearl 1:
The mnemonic FHL (F orce , H eight , L ength ) is helpful when considering muscle properties that influence neuromodulator treatment of the frontalis ( Fig. 16.1 A–E).
Forehead height, measured from the hairline to the top of the brow, differs considerably from person to person but is on average 5 cm in women and 6 cm in men. Occasionally, individuals have very short forehead height that requires modification in neuromodulator treatment. Vertically oriented, the frontalis muscle interweaves inferiorly with the corrugator supercilli and orbicularis oculi. Superiorly, it is ensheathed by the galea aponeurotica. The frontalis is characterized as both a distinct muscle and as a part of the digastric fronto-occipital muscle, which covers the skull and contains a central galea connection. Although generally considered to be fan-like, the shape of the frontalis muscle varies appreciably between individuals. This variation corresponds with the formation of lines with muscle contraction, ranging from single and deep to numerous and fine. On histology, forehead horizontal rhytids correspond with epidermal thinning as well as decreased elastin and collagen VII expression at the rhytid “base,” and are measured in depth from .0399 to .0758 mm. In cases where botulinum toxin type A injection is not sufficient to address horizontal forehead lines due to severity in depth or low position, soft tissue filler may be indicated.
Pearl 2:
Be cautious of individuals with moderate and severe deep horizontal forehead lines at rest. They developed these lines to compensate for brow- or eyelid ptosis.
Frontalis patterns of contraction
Frontalis muscle contraction is transmitted to the dermis via short fibrous bands called retinacula cutis, resulting in horizontal line formation. The transmission of muscle force is influenced by the thickness of the forehead superficial subcutaneous fat compartments, newly defined by Cotofona and colleagues. The frontalis muscle is the only elevator of the brow. Forehead motion for some individuals may be bidirectional, with the upper forehead skin moving caudally and the lower forehead skin moving cranially, converging at the second horizontal forehead line. This line has been termed in a recent publication the “line of convergence” or “C-line” (see Fig. 16.1 A and B). In patients with bidirectional frontalis motion, neuromodulators should be avoided below the C-line so as to minimize the risk of brow ptosis.
The exact configuration of horizontal forehead lines differs with muscle fiber arrangements and muscle contraction strength. For example, some individuals display considerable overlap of midline frontalis fibers, while others have a fibrous midline with little to no muscle fibers, which can result in straight or wavy forehead lines. Over the past few years, a new series of anatomic correlations between frontalis fiber patterns and associated horizontal forehead lines have been defined ( Fig. 16.2 ).
Pearl 3:
For any patient with deep horizontal forehead lines, consider treating only brow depressors first. Reevaluate the patient in two weeks for treatment of frontalis.
Brow position
Pearl 4:
When performing neuromodulator treatment of the frontalis muscle, priority should be placed on brow height over brow shape.
Eyebrow position depends on the dynamic between the frontalis and the brow depressors—procerus, corrugator supercilli, and depressor supercilli ( 
). Often, a compromise must be achieved between treating horizontal lines and maintaining brow height. The authors’ recommendation is to either cotreat brow depressors at the same time as the frontalis muscle, or to first treat brow depressors and then reevaluate the patient 2 weeks later for frontalis treatment.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here
