To meet increasing consumer demand, numerous aesthetic tools have been developed to combat facial ageing, restore normal anatomy, and optimise beauty. One such treatment is botulinum toxin type A (BTX-A).
Product Selection and Reconstitution
While there is some data comparing the various formulations of BTX-A, all approved products are effective and can be used to treat the various facial areas, some ‘off-label’. Become familiar with the performance of your chosen formulation and consider patient preference and history, as these are important factors in achieving positive outcomes.
Labeling states that BTX-A formulations should be single-use, reconstituted only with sterile, preservative-free 0.9% sodium chloride, and stored in a refrigerator between 2° to 8°C upon reconstitution and administered within 24 hours of reconstitution.
Unopened vials should also be stored in a refrigerator between 2° to 8°C with the exception of incobotulinumtoxinA which can be stored at room temperature up to 25°.
These storage recommendations stem from concerns regarding potentially reduced potency and increased risk of infection, but sometimes present a financial burden to follow in a clinical setting.
Studies have found that onabotulinumtoxinA may be used up to 6 weeks after reconstitution without loss of efficacy.
Wrinkle pattern
Common wrinkle-related concerns in the upper face include horizontal forehead lines, glabellar lines, and lateral canthal lines. Differences in individual anatomy and dynamic muscle movement can produce a variety of static and dynamic wrinkle patterns. These different patterns, in turn, require varying BTX-A injection patterns for effective treatment. The primary muscles involved in glabellar contraction include the corrugators, orbicularis oculi, procerus, and depressor supercilii, with occasional contributions from frontalis and nasalis
Frontalis is the predominant muscle underlying the forehead skin, and is the sole eyebrow elevator. The vertical orientation of its muscle fibres results in horizontal forehead lines with muscle contraction.
Frequently quite symmetrical and rectangular in shape, the frontalis muscle originates cranially from the tendinous galea aponeurotica and travels at uniform depth beneath forehead skin (~3-5mm on average) to interdigitate with muscles between the eyebrows; namely, corrugator supercilii, procerus, depressor supercilii, and medial portions of orbicularis oculi.
Laterally, the frontalis muscle terminates at the temporal fusion line. Of note, all these other muscles counteract the function of frontalis by collectively acting as eyebrow depressors.
Orbicularis oculi is a broad, flat oval-shaped muscle that encircles the eye and is comprised of orbital and palpebral parts.
The orbital portion refers to the outermost portion of the muscle which overlies the orbital rim, originating from the nasal part of the frontal bone, frontal process of the maxilla, and the medial canthal tendon.
Superiorly, this portion interdigitates with the frontalis muscle, and acts as a sphincter muscle involved in voluntary eyelid closure (such as forced squeezing or winking). The palpebral portion of orbicularis lies within the upper and lower eyelids, and is further subdivided into the preseptal and pretarsal sections.
The preseptal area lies in front of the orbital septum, originates from the medial palpebral ligament and inserts at the lateral palpebral raphe, and is involved in both voluntary eye closure and keeping the eyelids closed during sleep. The innermost pretarsal portion arises from the medial canthal tendon and overlies the tarsal plates; this portion is primarily involved with involuntary blink closure.
The circular geometry of orbicularis oculi results in vertical muscle fibre orientation (resulting in horizontal wrinkling) at the lateral and medial points, and horizontal fibre orientation (vertical wrinkling) at the superior and inferior points, and angled fibres in between.
Assessment
Patient Preparation
As with any treatment, patients should be screened for contraindications prior to BTX-A treatment.
These include hypersensitivity to any BTX-A preparation or to any components in the formulation, and infection at the proposed injection site.
AbobotulinumtoxinA may contain trace amounts of cow’s milk protein; as a result, patients known to be allergic should avoid this formulation.
Patients receiving treatment of BTX-A and aminoglycosides, or any other agents interfering with neuromuscular transmission (e.g. tetracyclines, polymyxins, penicillamine, anticholinesterases, and calcium channel blockers, amongst others), or muscle relaxants, are advised to do so with caution given possible potentiation of BTX-A effect.
Similarly, patients with neuromuscular disorders such as myasthenia gravis, Eaton-Lambert syndrome, and amyotrophic lateral sclerosis should ideally not be treated.
BTX-A amount of excretion in breast milk of nursing mothers is unknown; as a result, it should be avoided in both pregnant and breastfeeding women.
Individual physicians have differing levels of comfort in treating patients with disorders or medications affecting bleeding and clotting.
Additional considerations include recognising the presence of psychiatric disease or body dysmorphic disorder (BDD) and patients deemed to have unrealistic goals.
Patient position
Ideally, the patient will be seated upright with their head at the height of the injector’s shoulder and supported by a headrest. Alcohol pads can be used to remove makeup, facial oils, and debris from injection sites; chlorhexidine or other anti-septic products are more commonly reserved for dermal injections.
Creation of the Treatment plan
Creation of individual treatment plans requires consideration of numerous factors, and distinguishing between what the patients wants and what professional judgement suggests is needed.
The initial assessment should include consideration of static and dynamic features.
Static considerations include eyebrow position and shape, forehead height, volume changes, overall facial symmetry, and presence of static rhytides.
Palpation of muscle bulk and skin thickness is also important as these may impact the quantity and depth of BTX-A injection.
Dynamic assessment is especially important because while facial anatomy is fairly preserved amongst individuals, the fashion in which muscles of facial expression are used may vary greatly.
Raising the eyebrows allows assessment of forehead wrinkles. Lateral canthal wrinkles are assessed by first smiling and then closing the eyes tightly without moving the cheeks. Both orbicularis and zygomaticus major muscles contribute to lateral canthal lines when making a full smile, while closing the eyes without smiling highlights rhytides arising from orbicularis oculi.
In general, neuromodulator treatment should be based on muscle bulk, distribution, and activity.
The procerus muscle is a thin, pyramidal-shaped depressor of the brow, which originates in fascia at the inferior nasal bone and becomes more superficial, inserting in the glabella where it interdigitates with the frontalis muscle. The procerus muscle depresses the medial portion of the brow, and also contributes to horizontal rhytides of the nasal dorsum.
Corrugator supercilii is another brow depressor that contributes to frowning, squinting, and vertical rhytides in the glabella and lower forehead. Its origin lies in the medial orbital rim and it runs superiorly and laterally to insert into the dermis, though the exact area of insertion is highly variable.
Importantly, the corrugator supercilii muscle travels at different depths along its path, which must be considered in treatment planning. It is deepest at its bony origin and becomes progressively more superficial, eventually inserting into the dermis. Limiting BTX-A spread to surrounding muscles is particularly important in the glabellar region since the muscles here interdigitate and function together.
The depressor supercilii muscle pulls the medial eyebrow downwards, further contributing to frowning and squinting. Some consider this to be part of the medial orbicularis oculi muscle. It originates from the frontal process of the maxillary bone often as two distinct heads, typically 1cm above the medial canthal tendon. The insertion point is roughly 13-14mm superior to the medial canthal tendon, lying lateral to the insertion of corrugator supercilii.
Eyebrow position and shape
A key goal of upper face neuromodulator treatment is optimising brow shape and position.
Eyebrow position should be palpated in relation to the orbital rim. As mentioned, the eyebrows have one elevator (frontalis), which is counterbalanced by several brow depressors (corrugator supercilii, procerus, depressor supercilii and portions of orbicularis oculi). Frontalis gives rise to horizontal forehead wrinkles, while corrugator and procerus cause vertical and horizontal glabellar rhytides, respectively. In order to create an individual treatment plan, precise assessment of brow elevator and depressor activity is critical.
For example, if the procerus muscle exerts significant downwards pull on the medial brow and creates a transverse lower glabellar rhytid, it would be important to inject that muscle if the goal of treatment is to achieve medial brow elevation. Conversely, if the frontalis muscle does not extend far laterally, then it may not be necessary to inject the forehead laterally.
if one fails to consider how much the frontalis muscle is contributing to holding up the brow when treating horizontal forehead rhytides, this may lead to eyelid ptosis. This is particularly true in the setting of a dehisced levator palpebrae muscle and can be explained by Hering’s law, which states that both eyes behave as a single organ with equal and simultaneous innervation to the extraocular muscles.
Symmetry
Assessment for overall symmetry in the upper third of the face is very important when considering forehead and glabellar injection patterns. Some degree of eyebrow asymmetry will commonly be noted, and, in such cases, a decision must be made as to whether to elevate the lower brow, lower the elevated one, or a combination of both.
Forehead height
Individuals with taller foreheads may require more than one row of BTX-A injections into the frontalis muscle to effectively treat horizontal forehead lines. More than one row of injections may also be considered when wrinkles extend into the hairline, such as in patients with a receded hairline. Conversely, those with a short forehead may require lower doses of BTX-A in order to avoid overly weakening the lower frontalis fibers, which can lead to eyebrow and eyelid ptosis.
Volume changes
Assessment of cutaneous thinning, fat atrophy and bone attenuation is an important aspect of the initial assessment when considering BTX-A treatment. Volume loss on the forehead, temples, and lateral canthal region can make it challenging to achieve optimal results with neuromodulators alone. As a result, this observation should prompt consideration of combination treatment, such as with soft tissue fillers.
Analgesia and Needle Size
While minimizing patient discomfort is important in any procedure, BTX-A injections are generally well-tolerated.
However, some injectors prefer the addition of analgesic strategies such as use of ice packs, cooled needles, and topical anesthetics. Injection techniques to minimise pain can also include pinching the skin firmly in the treatment area.
While the FDA recommends use of 30- to 33-gauge needles for treatment of glabellar facial lines, 30-gauge needles are routinely used for BTX-A injections on the face.
Use of the 0.3cc U-100 insulin syringe with 30-gauge short Ultra-Fine II needle with its ease of use, cost efficiency, small size, accuracy of toxin delivery, and minimisation of pain or 32-gauge needles which are thinner than 30-gauge needles, they are more expensive.
Injecting
Recommendations for glabellar lines include intramuscular injections using 3 to 7 injection points (2 to 4 U onabotulinumtoxinA per injection point) targeting corrugator supercilii, procerus, depressor supercilii, as well as orbicularis oculi; typical total doses can vary from 12 to 40 U of onabotulinumtoxinA.
Lateral Canthal Obiculris Occuli indication include 1 to 5 intramuscular injection points per side targeting lateral orbicularis oculi muscle fibers (1 to 4 U onabotulinumtoxinA per injection point).
Treatment of frontalis should not completely eliminate the ability to elevate the eyebrows, although it will definitely be reduced. A global aesthetics consensus group recommends a total of 8 to 25 units (U) of onabotulinumtoxin A for treatment of horizontal forehead lines, via an intramuscular or intracutaneous approach. This can be done through 4 to 8 (non-microdroplet; 2 to 4 U onabotulinumtoxinA per injection point) or 8 to 20 injection points (microdroplet; 0.5 to 1.5 U onabotulinumtoxinA per injection point).
After-Procedure Care
Evidence-based recommendations on optimal post-procedure care are lacking. Some have recommended that patients exercise injected muscles for up to 4 hours after treatment to enhance cellular uptake. This is based on the premise that muscular activity may accelerate the binding of toxin to the cholinergic receptor.
With this in mind, it is possible that facial exercise may only be indicated for 1 hour as most binding of toxin will be complete by that time. Facial exercise after treatment with BTX-A is a safe intervention that may possibly lead to an earlier onset in clinical improvement, and may be recommended to patients for whom this is important. Asking patients to perform facial exercises and remain upright for 1 hour may be more logical than the frequently recommended 4 hours.
Patients are also commonly asked to avoid massaging the treated area after injection to prevent unwanted product spread beyond the treated area. This recommendation is similarly felt to be low risk but there is no data to support this practice.
Conclusion
Neuromodulators are an excellent treatment option for the upper face. Understanding functional anatomy of the underlying muscles of facial expression is key if one is to achieve aesthetically pleasing, natural outcomes. Similarly, while clinical trials rely on standardised treatment protocols, optimal outcomes may be best achieved when treatments are tailored to the individual patient, based on anatomy, assessment, and treatment goals.
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