Revisiting the anatomy of the
glabellar muscles

A regular column on anatomy by Prof Sebastian Cotofana MD, PHD, PHD.

The glabellar region is the region between the eyebrows located at the transitional zone between the forehead and the nose. The term ‘glabella’ originates from the Latin term glabellus which means smooth, hairless, without projection. Due to the absence of hairs in this region, skin wrinkles are easily identifiable, which can prompt aesthetic patients to have these folds removed, preferrably by the injection of neuromodulators.

The skin folds, or glabellar lines, formed during the activation of the glabellar muscles are horizontal and vertical, and are predominantly formed when looking angry or sad. When these folds disappear when the face is a rest, ie, not performing any facial expression, they are termed dynamic folds, but when these folds are constantly visible, even during a relaxed facial expression, they are termed static folds – the latter more frequently associated with facial ageing.

Because glabellar skin folds are often associated with facial ageing and an angry demeanour, they can be perceived in a negative way. This is unlike crow’s feet, which are associated with more positive connotations due to their connection with smiling – hence why they are also termed smile lines and are a feature of the ‘Duchenne’ type of smile.

For glabellar lines, neuromodulator products are the product of choice. The toxin paralyses the targeted muscles temporarily; the duration and effect of which is dependent on the type of toxin used, the reconstitution volume and the number of units administered. Relaxing the glabellar muscles results in the inability to contract these muscles and, as a consequence, no skin folds are formed during facial expression and static folds are improved due to the absence of a baseline muscle tone.

It is paramount for every injector to understand how the skin folds relate to the underlying muscles and to interpret what is visible on the skin’s surface in terms of the structures beneath it, which are not directly visible to the injector. The reasoning behind this decoding process is because only when administering the neuromodulator directly into the culprit muscle can the skin fold be treated. If, instead of the muscle, a skin fold is targeted (as it was suggested many years ago when treating the glabella), less toxin product reaches the culprit muscle which results in a reduced treatment duration and reduced effect strength. In addition, there is the risk that the product reaches other structures or muscles that should not be treated, with adverse events being the respective consequence.

Here is an example: If the glabella is injected 1 or 2 cm above the orbital rim for injections into the tail of the corrugator muscle, the frontalis muscle is actually targeted instead. This results in a weakening of the sole eyebrow elevator which will result in eyebrow ptosis.

Recent research derived from MRI-based studies has indicated that the muscles of the glabella have the same length, width and thickness independent of their skin fold pattern. This means that, independent of the wrinkle pattern that can be observed on the skin surface, the underlying muscles can be precisely targeted with the same and identical injection algorithm without the need for adjustment in injection location. Adjustments for dosage depending on the individual aesthetic case are mandatory and will continue to rely on accurate patient assessment.

Another recent study on the same topic has revealed that during various facial expressions, multiple muscles are active at the same time. This finding is novel because in the past it was always assumed that during a ‘surprised’ facial expression only the frontalis muscle acts as an eyebrow elevator and all depressor muscles (which are the muscles of the glabella) are inactive. However, according to this new concept, both antagonistic muscle pairs, elevator and depressors, are active at the same time. This indicates that during facial assessment the strength of the elevator and the depressors needs to be evaluated to predict the maximal elevation or depression that could be potentially expected after the neuromodulator treatment. Clinically this would mean that the strength of the frontalis muscle should be evaluated before targeting lateral canthal lines and expecting eyebrow elevation; a weak frontalis muscle is unable to elevate the tail of the eyebrow, independent of how much toxin is injected into the lateral orbicularis oculi muscle.

The above research findings provide a deeper understanding of facial anatomy which is essential for superior clinical outcomes and reduced adverse events, especially when treating the glabella with neuromodulators. AMP

Sebastian Cotofana, MD, PhD, PhD, is a globally renowned anatomist specialising in facial aesthetics. With a distinguished career in anatomical research and dissections, he has become a leading international expert, lecturing in over 35 countries.

Professor Cotofana earned his medical degree in Munich, Germany, followed by residency in Trauma Surgery. He holds two PhD degrees—one in Medical Sciences from Ludwig-Maximilians-University and another in Anatomy from Paracelsus Medical University.

His career spans several prestigious institutions, including Ross University School of Medicine, Albany Medical College and Mayo Clinic, where he became a Full Professor of Clinical Anatomy in 2023. He is also the CEO of Cotofana Anatomy Corp, a global academy focused on teaching anatomy to healthcare professionals. Additionally, Prof Cotofana holds adjoint and honorary professorships at Vanderbilt University, Queen Mary University, Pirogov University and several others worldwide. Prof Cotofana’s contributions to scientific literature include over 250 peer- reviewed articles, book chapters and online communications.