This article refines our understanding surrounding the forehead in general and more specifically of the anatomy and function of frontalis, a common target for anti-wrinkle injections. The author enrolled a cohort of volunteers with a wide range of ethnic backgrounds and sex distribution. The aim of the study was to highlight the heterogeneous nature of the forehead dimensions and frontalis muscle relating this to appropriate neuromodulator treatment. The authors introduce the concept of the line of convergence, or C-line. The results show that males have a statistically significantly longer forehead than females but that there is no ethnic difference. The median number of forehead rhytides is four, with no association with sex, ethnicity or forehead length. All patients had a C-line – the line divides the lower brow elevating part from the upper hairline depressing part of frontalis. This line was 39mm above the brow in males compared to 34mm for females but proportionally at around 61% of the forehead length above the brow in all cases. Forehead shortening on frontalis contraction was approximately 13mm in men and 8mm, the authors postulating this difference is due to frontalis power. The bidirectional movement of the frontalis explains why paralysis of the upper muscle, above the C-line, improves forehead rhytides without causing brow ptosis. Safe injection practice should involve staying at least 2cm above the brow to spare the elevating part of frontalis. The increased range of movement in male patients indicates that a higher neuromodulator dosage will be required to achieve effective muscle paralysis. The article adds knowledge to explain a well-established clinical practice. It is a relatively small study but employs robust statistical analysis with significant results that can help maintain patient safety when using neuromodulators. It would benefit from detail regarding lateral frontalis sparing as a technique for brow elevation. This, together with assessment of glabellar complex and superior orbicularis oculi depressor paralysis on brow position would add weight to the paper.
