Where and how to use botulinum toxin on the face and neck – Indications and techniques

INTRODUCTION

With its discovery as a substance that can be used to treat dynamic glabellar frown lines in 1992, botulinum toxin (BT) is now increasingly being used for treating dynamic rhytides elsewhere on the face, contouring the face and even lifting it. Some of these are US Food and Drug Administration (FDA) approved, while others are considered off-label. The understanding of the usage of BT has evolved a lot, from its different types to newer indications, techniques employed for injection to variations in dosages to side effects.

This article aims to review and present the different cosmetic indications and injection techniques of BT on the face that has been reported in literature so far.

INDICATIONS

The recent published statistics report by the American Society of Plastic Surgery reported over 7.4 million BT type A treatments in 2019.^[1] It is the most requested for minimally invasive cosmetic procedure worldwide.

BT is mainly used as a cosmetic procedure for smoothening or softening dynamic wrinkles on the face. It is also used to soften skin lines, to contour and lift the face.^[2] The cosmetic indications are treated with BT type A and the subtypes mostly used are onabotulinum, abobotulinum, and incobotulinum.

A smooth, wrinkle-free face is synonymous with youthfulness.^[3] The increasing awareness of minimally invasive procedures as anti-aging tools is leading to increased BT treatments being performed due to its effectiveness, minimal side effects, and minimal downtime.

The US FDA approved indications of onabotulinum type A are moderate-to-severe glabellar frown lines associated with procerus and/or corrugator muscle overactivity, moderate-to-severe lateral canthal lines associated with orbicularis muscle overactivity, and moderate-to-severe horizontal forehead lines associated with frontalis overactivity.^[4] The FDA approval for abobotulinum A and incobotulinum A is limited to the treatment of glabellar lines only.^[5]

BT injections are appropriate for those patients who have cosmetic concerns related to hyperactivity of muscles or groups of them. Younger patients with good skin elasticity benefit more.^[6,7] Static rhytides can only soften with the treatment. The various indications for which BT type A can be used are enumerated in Table 1. The target muscles and their mechanisms of action are also mentioned.

The patient should not have any contraindication to the treatment like being allergic to the toxin or its components, suffering from a neuromuscular disorder like myasthenia gravis or Eaton-Lambert syndrome, have an active infection at the site of injection, be on any neuromodulator drugs, etc. [Table 2].^[7]

The upper face muscles are muscles of expression. Targeting them can also lead to a change in the emotional attributes of the face. The face can look less angry after treatment of the glabellar frown lines or less worrisome after the treatment of the forehead horizontal lines.^[8]

BT is also used to create a balance in a particular anatomical area among the group of antagonist muscles by an indirect action. This is exemplified by treating the elevators causing a stronger pull of the depressors and vice versa. Certain asymmetries can also be tackled with the use of BT by utilizing the action of antagonist muscle groups.^[9]

RELEVANT ANATOMY

Before embarking on treatment with BT, it is pertinent to have a thorough knowledge of the muscles involved to treat a particular indication. This gives a better insight into the science of the treatment as well as helps to deliver the desired clinical outcomes with minimal side effects.

Most of the BT injections are intramuscular with its action on the neuromuscular end plate causing chemical denervation to the muscle, leading to its relaxation.^[10] An understanding of the interaction between muscle groups is essential. Injections are subdermal in those areas where the muscles are very superficial like the orbicularis oculi or where complete relaxation of the muscle is not desired such as the frontalis.

The muscle action is strongest at its origin and maximum dosage should be thus injected at the site where the muscle originates. Those muscles whose fibers insert into the skin can be targeted with intradermal injections and those which are superficial can be targeted with subdermal injections. Expression lines are formed perpendicular to the axis of muscle traction.

Individual muscles specially those present in groups, should be respected, as each muscle has a unique action and has the potential of disrupting the balance of the facial features if inadvertently targeted. The muscles of the face are depicted in Figure 1. Their origins and insertions are indicated in Table 3.

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Figure 1:

The muscles of the face.

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INJECTION TECHNIQUES

The treatment with BT is considered as one of the most gratifying in terms of clinical outcomes. The results are dramatic when used for expression lines. Doses less than those used for the upper face are used to give results in the lower face and neck for indications such as softening of lines, creating a balance, and contouring or correcting asymmetry.^[11]

It is important to know the correct injection points to prevent inadvertent complications. The correct dose, depth of injection, and centering, apart from a thorough knowledge of the anatomy, are all to be paid attention to for optimal clinical outcomes. It may sometimes be prudent to inject the antagonist group of muscles to maintain harmony and to avoid unopposed hyperactivity of the antagonist muscles. General considerations are shown in Table 4.

FRONTALIS INJECTIONS

This is the muscle targeted to treat dynamic horizontal forehead lines caused by the contraction of this muscle. These lines appear on raising the brows.

Not freezing the forehead and maintaining a little activity of the muscle are the key to a good esthetic result, as the frontalis is the only elevator of the brow. The lower 1–2 cm of the muscle above the orbital rim should not be treated to prevent a brow ptosis.^[12] When numerous fine lines are present on the forehead, it is prudent to use a hyperdiluted form of BT and inject intradermally, to tackle the insertion fibers. Injections should be at an angle so as not to hit the periosteum to avoid a painful injection.

The muscle shows two patterns anatomically. The first is a single, broad muscle which gives rise to continuous wrinkles on the forehead. The second pattern is a bifid muscle, with a central separation, which gives rise to non-continuous wrinkling on the forehead, on either side of the midline. Clinically, four patterns are visible. Their injection points are shown in Figure 2.

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Figure 2:

Frontalis patterns. (a) Full form causing straight lines across the entire forehead; (b) central type forming lines over medial half of orbital rims and joining centrally; (c) V-shaped creating gull-shaped lines across the forehead; (d) lateral located over lateral half of orbital rims and their injection points.

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GLABELLAR INJECTIONS

The glabellar complex is formed by the procerus, corrugator supercilii, and depressor supercilii muscles. All these are depressors of the brow. These muscles are injected to treat the glabellar frown lines and raise the brows. Horizontal, vertical, and oblique frown lines are formed by these muscles along with the medial fibers of the orbicularis oculi and lower frontalis fibers.

Different patterns of the glabellar complex muscles can give rise to different patterns of frown lines [Figure 3]. The conventional injection technique is shown in the figure.

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Figure 3:

Glabellar wrinkle patterns and their wrinkle points.

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Procerus is the first muscle to be injected. The first point is marked at the intersection between two lines drawn from the medial brow to the contralateral medial canthus on each side. This is where the maximum bulk of the procerus is. If the muscle is long, then another point is marked a cm above the first point. Injections are perpendicular.

The corrugators have a medial and lateral part. Injections into the medial part are deeper, into the muscle bulk. The lateral injections are more superficial, taking care not to be too superficial so that the interdigitating frontalis fibers can be avoided. The conventional injection technique is shown in Figure 4a. Additional benefit has been found by giving one injection on either side into the lateral eyebrow leading in further reduction in the glabellar frown lines.^[12]

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Figure 4:

Injection points for (a) corrugator supercilii and (b) depressor supercilii.

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Injections should not cross the mid-pupillary line to avoid ptosis of the brow. The non-dominant thumb should be placed at the supraorbital ridge to prevent diffusion into the intraocular muscles which may lead to ptosis of the upper eyelid. Caution should be exerted to keep dosages low in elderly patients in whom the orbital septum may be weak causing diffusion into the intraocular muscles.

The medial brow is elevated by injecting the depressor supercilii [Figure 4b].

ORBICULARIS OCULI INJECTIONS

It is a superficial muscle. Injections should be superficial, raising a bleb. Superolateral fibers are injected to raise the lateral brow. Lateral fibers are injected for the crow’s feet. The needle should be directed away from the orbit, a cm away from the orbital rim.

The patterns of crow’s feet that are formed and their injection points are shown in Figure 5a. Multiple injections are required as the muscle is large and is innervated diffusely.^[13] The inferior part of the muscle is injected 3 mm below the ciliary margin to treat the inferior orbital lines, also known as “jelly rolls.” Injections can be given at two points after stretching the lower eyelid skin. A total of 1–2 units are recommended [Figure 5b].

Diluted BT (microbotulinum toxin) can also be given in the under eye area. A positive snap test, lower eyelid puffiness, and prior lower lid blepharoplasty are contraindications to infraorbital injections.^[14]

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Figure 5:

Injection points for orbicularis oculi. (a) Lateral (crow’s feet); (b) inferior (jelly rolls).

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BROW INJECTIONS

Although the muscles injected for lifting or shaping the brow have already been discussed above, brow injections deserve a special mention as they are advanced injections. Lifting and shaping depend on the interplay between the only elevator, the frontalis, and the depressors. The medial depressors are injected to cause a medial elevation and lateral depressors for lateral elevation.

A full lift requires injecting all the muscles involved with depressing the brow. Lifting the brow can do away with lateral hooding of the upper eyelid which gives a tired look to the eyes. Injection points are shown in Figure 6. Not all patients respond to a chemical brow lift. Those with excessive brow ptosis or those who use the frontalis to compensate for the brow ptosis do not benefit much.

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Figure 6:

Brow lift injection points. (a) Lateral; (b) medial.

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NASAL INJECTIONS

The nose has a complex of multiple muscle groups [Figure 7]. The muscles of the nose are injected to treat bunny lines, a nasal flare, or a depressed nasal tip. The major muscle involved in the formation of bunny lines is the transverse nasalis. It must be noted that other muscles such as the procerus, the LLSAN, and the medial fibers of the orbicularis oculi may also contribute, depending on the pattern of lines formed. Assessment after 4 weeks is prudent to address minor muscles if the lines remain. A study from Korea showed that in 90% of the cases, the LLSAN gives off fibers to the nasalis. The injection point is shown in Figure 8a. Injections should not be made too lateral or inferior to prevent diffusion into the levator labii superioris, LLSAN, or levator anguli oris to prevent a lip droop.

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Figure 7:

The muscles of the nose.

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Figure 8:

Injection points for the (a) nasalis; (b) dilator nasi; (c) depressor septi nasi; (d) Yonsei point for gummy smile.

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The alar nasalis (dilator nasalis) muscle is injected to reduce a nasal flare or nasal flutter [Figure 8b]. The depressor septi nasi is injected to treat a nasal tip droop. The patient is asked to stretch the upper lip and injection should be half-tip deep into the muscle to prevent diffusion into the orbicularis oris, Figure 8c. These injections only work when there is a flare or nasal tip droop is observed on animation. Treating the nasal droop may lead to the elongation of the upper lip.

According to Tjan et al., an excessive shows of the gingival tissue of 3 mm or more is defined as a gummy smile.^[15] The major muscle involved is the LLSAN, with LLS and zygomaticus minor (ZMi) being the minor ones. Injections should be of low dose and superficial to prevent lip droop. The conventional injection point is the Yonsei point, 1 cm lateral and below the nasal ala. This point forms the center of the triangle formed by the LLSAN, LLS, and the ZMi muscles [Figure 8d].^[16]

The nasolabial folds can be softened slightly with injections into the lip elevator complex. Just a unit should be injected just above the nasolabial groove.

PERIORAL INJECTIONS

Smoker’s lines are caused by an overactive orbicularis oculi muscle and aging in this area. Injections should be of low dosage, around 1 U in each quadrant and superficial. The mouth’s functional competence may be lost with excessive dosing of the orbicularis oris muscle. Injections at these points also lead to a lip eversion.^[17]

The marionette lines develop as a part of aging. Targeting the depressor anguli oris causes an upturn of the corner of the mouth. The injections must be very precise to prevent inadvertently hitting the levator anguli oris leading to an asymmetrical smile [Figure 9]. These injection points should be slightly internal to the cross points of the extension of the nasolabial fold and the jaw line.^[18]

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Figure 9:

Injection points for orbicularis oris (smokers lines). (a) Option I; (b) option II; and (c) marionette lines.

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CHIN INJECTIONS

The peau d’orange appearance of the chin is caused by a hyperactive mentalis muscle. Injection techniques are shown in Figure 10. The superficial fibers of the mentalis should be tackled. Deeper injections closer to the lower lip may cause a lower lip droop, which can be avoided by injecting lower in the chin. Injecting the muscle also relaxes the mental crease increasing the chin length slightly.

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Figure 10:

Injection point options for mentalis.

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MASSETER INJECTIONS

A hypertrophied masseter leads to a broad face and a square jaw. It is injected to slim and contour the lower face and define the jaw. The superficial and deep parts of the muscle should both be targeted. To give a “sunken cheek” appearance, the superior portion of the muscle can be targeted. The safe area and the injection points are marked in Figure 11. Care should be taken to be inferior to the line drawn from angle of the mouth to the lower end of the ear.

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Figure 11:

(a) The masseter muscle and its relationship to the risorius and (b) injection points.

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NECK INJECTIONS

The platysma is a depressor of the face and treating it lifts the jaw and lower face. The Nefertiti Lift is a “mini lift,” defining the border of the jaw and angle of the mandible.^[9] Injection should stay posterior to the line of extrapolation of the nasolabial fold down to the mandible.

Hyperactivity due to the platysma supporting the ptotic face and loss of tone of the anterior part leads to vertical bands, called “Turkey neck” deformity. Younger patients with good skin elasticity respond better. The horizontal neck bands form due to increased skin laxity. Continuous movement leads to static creases. Injections are intradermal and deeper injections should be avoided to prevent hitting a perforating vein. Injection points for neck indications are shown in Figure 12.

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Figure 12:

The injection points for the Nefertiti lift (red) and platysmal bands (blue).

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CONCLUSION

Knowing the play between antagonist muscle groups, the anatomy of muscles involved in causing an indication amenable to treatment and adopting the right injection technique gives a desirable clinical outcome with BT injections with balance and harmony to the face.