Botox injections and facial muscles

Since Botox removes wrinkles by preventing muscle contraction, practitioners must know all about the underlying facial muscle anatomy to get the best results and avoid complications. Face muscles are complex and a thorough understanding of both contracting and counterbalancing muscles is needed. Their relationship must be understood before injecting Botox.

The muscles of the upper part of the face that are usually treated with Botox include the forehead ('Frontalis') for forehead wrinkles, the muscles in and above the eyebrow ('Corrugator/Depressor supercilli complex'), the frowning muscle between the eyebrows ('Procerus'), crinkling and crows feet muscles surrounding the eye 'Orbicularis oculi'), and 'bunny lines' muscle over the nose ('Nasalis'). In the lower half of the face, the wrinkles around the mouth may be treated by injecting small doses of Botox into the 'Orbicularis oris' (muscle circling the mouth) and the downward 'marrionette line' depressions at the lower corners of the mouth ('Depressor anguli oris'), while neck sagging is treated injecting Botox into the Platysma muscle (goes from the lower face, over the jaw and down the neck).

Facial expression muscles
The main expression muscles to be given Botox injections are:
(A) forehead (Frontalis)
(B) eyebrow (Corrugator and Depressor supercilli complex)
(C) around the eyes (Orbicularis oculi)
(D) between the eyebrows (Procerus)
(E) Platysma
(F) muscle over the nose (Nasalis)
(G) around the mouth (Orbicularis oris)
(H) corners of the mouth downwards (Depressor anguli oris)
(Pictures from Emerging Pharma, Inc.)

Botox injections for forehead wrinkles.

Forehead wrinkles are caused when the Frontalis muscle contracts. The forehead ('Frontalis') muscle starts from the top of the skull and anchors itself to the bony ridge above the eye. Its fibers interweave with the muscles between the eyebrows, above the eyebrows and surrounding the eye.

When a person contracts the forehead muscle, horizontal wrinkles appear in the forehead and the eyebrows raise. An injection of Botox will weaken this muscle so that it cannot wrinkle up. The forehead muscle has more connective tissue in the middle of the forehead than at the sides, so needs less Botox there.

Botox injections for frown lines

Counterbalancing the muscle responsible for forehead wrinkles are the muscles responsible for frown lines.
These are between the eyebrows (Procerus), above the eyebrows (Corrugator) the mid eyebrow area (Depressor supercilli) and the outer edge of the eyebrow (the above side part of the Orbicularis oculi). It is worthwhile to take some time looking at the picture below to familarise yourself with these muscles and their latin names.

movement of these muscles causes frown lines
(Pr) Procerus
(C) Corrugator
(DS) Depressor supercilli
(O) Orbicularis
(Illustration by Lauren Chavell of Medical Imagery)

If you are having yourself treated with Botox for forehead wrinkles only, you need to consider the frown line area between the brows too. There is a good reason for this. There is a significant risk that your entire browline will drop quite a bit unless the frown muscles are also treated with Botox.

This is because, after having your forehead wrinkles treated with Botodx the frowning muscles will be frowning downwards the same as usual, but the eyebrow-raising forehead muscles will not be pulling upwards counteracting their pull! It is important to choose a practitioner who understands the relationship between the two sets of muscles. Don't be afraid to pester your practitioner with questions on where exactly they intend to inject, and why.

The best results regarding brow height and shape are usually obtained through either a low dose of Botox injected into the forehead, or injecting Botox into both the forehead wrinkles area and the frownline wrinkles area.

We have already mentioned the 'central brow depressors' these are the:-
Procerus muscle between the eyebrows,
Corrugator muscle above the eyebrows, and
Depressor supercilli - the muscle that brings down the inner corner of the eyebrows into a frown.

As well as these, you might want to consider the upper side part of the muscle encircling the eye ('Orbicularis oculi'). It is what causes the outer edge of the eyebrows to droop with age, and drooping outer edges to eyebrows can give away your age like almost nothing else.

The Procerus muscle starts low down on the nasal bone and connects with the skin over the top of the root of the nose. Its fibers are interwoven with the 'Orbicularis oculi' surrounding the eye, the 'Frontalis' in the and Corrugator muscles above the eyebrow.

When we contract the Procerus muscle we cause a horizontal wrinkle on the bridge of the nose because the contraction is shortening the muscle from top to bottom. This brings the brows down over the top of the nose.

The Corrugator muscle above the eyebrow, along with the Depressor supercilli (muscle at the inner corner of the eyebrows), is what causes the up and down vertical forehead wrinkles. The Corrugator muscle starts some distance above the middle of the eyebrow, passes downwards through fatty tissue above the eyebrow and connects to the skin in the center of the eyebrow. The Depressor supercilli muscle is below the Corrugator muscle and also helps cause nasty vertical frown lines.

If Botox is injected anywhere near the Corrugator muscle, it will also work on the Depressor supercilli as well because they are very close together. For all intents and purposes they are a single unit.

Drooping brows are caused by upper outside of the muscle surrounding the eye. If this muscle is injected with Botox at the same time as the brow depressing muscles are injected, the eyebrows can be lifted up to 3mm. This technique is called a 'chemical brow lift'.

Your practitioner must avoid injecting Botox too deep into the Orbicularis oculi surrounding the eyes, as the muscle is quite thin. 2 or 3mm will do.

The Orbicularis Oculi

The muscle surrounding the eye ('Orbicularis oculi') muscle is a ring-like striated muscle sheet that lies just below the skin. It is separated from the overlying dermis by a fibro-adipose layer that may be 4 to 6 mm thick underneath the brow region but that is less than 0.1 mm in thickness in the pretarsal portion of the eyelid where it terminates at the eyelid margin.7 The Orbicularis muscle is divided anatomically into three areas: the pre-orbital, preseptal, and pretarsal areas (Figure 3-6).

Figure 3-6
Figure 3-6. The Orbicularis muscle is divided into the pre-orbital, preseptal, and pretarsal portions based on both function and anatomy.
(Reprinted from Atlas of Clinical and Surgical Orbital Anatomy, JJ Dutton, ©1994, with permission from Elsevier.)

The pre-orbital portion of the muscle surrounding the eye ('Orbicularis oculi') muscle arises from insertions on the frontal process of the maxillary bone in front of the anterior lacrimal crest and from the common medial canthal tendon. Its fibers pass around the orbital rim to form an elliptical shape that is continuous at the side commissure and inserts medially just below their original points of origin.

In contrast, the palpebral portion of the muscle surrounding the eye ('Orbicularis oculi') muscle consists of two hemiellipses of muscle that are fixed medially and sidely at the medial and side canthal tendon complexes. While this portion forms a single anatomical unit, it is traditionally divided topographically into the pre-septal and pre-tarsal portions. The pre-septal portion is positioned over the orbital septum in both the upper and lower eyelids and appears to function largely by counteracting the opposing tone of the eyelid retractors. It also contributes to the lacrimal pump mechanism since it is associated medially with Horner’s muscle of the lacrimal sac. The pre-tarsal muscle surrounding the eye ('Orbicularis oculi') muscle originates from the superficial and deep portion of the medial canthal tendon complex. The superficial heads of the pretarsal portion insert into the anterior arm of the medial canthal tendon and run nearly parallel to the horizontal plane of the eyelid margin, while the deep heads invest the canaliculi and are involved with the lacrimal pump mechanism.

Contraction of the side portion of the preseptal and pre-orbital portion of the muscle surrounding the eye ('Orbicularis oculi') muscle causes the formation of “crow’s feet” or “smile lines” (Figure 3-7).8 These lines can be inactivated by injecting Botox into the pre-orbital muscle surrounding the eye ('Orbicularis oculi') muscle in the area just side to the orbital rim. usually 2 to 3 injections are used to distribute Botox to this area. It is important to palpate the region of muscle contraction so they caninactivate the side portion muscle surrounding the eye ('Orbicularis oculi') muscle. Care should be taken to avoid injecting within the orbital rim as this increases the likelihood of diffusion of the Botox behind the septum, which may induce an ectropion of the lower eyelid or upper eyelid ptosis.

Figure 3-7
Figure 3-7. Contraction of the side portion of the preseptal and preorbital portion of the Orbicularis oris muscle induces “crow’s feet” or “smile lines.”

Patients with main essential blepharospasm or hemifacial spasm may exhibit uncontrolled spasmodic contraction of the entire muscle surrounding the eye ('Orbicularis oculi') muscle complex.9 Essential blepharospasm is felt to arise from a central nervous system defect in the basal ganglion of the mid-brain.10 In contrast, hemifacial spasm is a disorder of the peripheral nervous system most usually associated with irritation of the 7th cranial nerve after it exits the brainstem. The spasm is felt to arise from irritation of the facial nerve by an adjacent artery that shares a common adventitial sheath.11,12 As its name implies, this process is usually uniside and may involve the Orbicularis oculi muscle as well as other muscles of facial expression including the muscles of the mid-face, lower-face, and neck region.

The muscle over the nose ('Nasalis')

The muscle over the nose ('Nasalis') or Compressor naris muscle arises from the maxilla and its fibers proceed upwards and medially, expanding into a thin aponeurosis that is continuous on the bridge of the nose with that of the muscle of the opposite side, and with the aponeurosis of the muscle between the eyebrows ('Procerus') muscle (see Figure 3-1). Contraction of the muscle over the nose ('Nasalis') depresses the cartilaginous part of the nose and draws the nasal ala toward the septum, creating ridges on the nasal bridge that have been referred to as “bunny lines” (Figure 3-8).

Figure 3-8
Figure 3-8. Contraction of the muscle over the nose ('Nasalis') creates ridges on the nasal bridge that have been referred to as “bunny lines.”

Zygomaticus Major and Minor

The Zygomaticus major muscle originates along the inferoside aspect of the orbital rim from the zygomatic bone, in front of the zygomaticotemporal suture, and descends obliquely and medially where it inserts into the angle of the mouth (see Figure 3-1). At its insertion near the mouth, it blends with the fibers of the Orbicularis oris and Depressor anguli oris, which act as its main counterbalancing. Zygomaticus minor arises just medial and inferior to Zygomaticus major and works in synergy with its larger side counterpart to form a functional complex. Contraction of the Zygomaticus muscle complex draws the angle of the mouth backward and upward, as in laughing. In individuals with hemifacial spasm or Meige’s syndrome, this muscle’s involuntary contraction can be psychologically disturbing to the patient as it elevates the side aspect of the upper lip and slightly opens the mouth.

The Orbicularis Oris

The Orbicularis oris is not a simple sphincter muscle like the muscle surrounding the eye ('Orbicularis oculi'); it consists of numerous layers of muscle fibers surrounding the opening of the mouth that are oriented in many different directions. It is partially derived from the fibers of other facial muscles that are inserted into the lips, and partly from fibers proper to the lips. Of the former, a considerable number are derived from the Buccinator muscle and form the deeper layers of the Orbicularis oris. Some of the Buccinator fibers—namely, those near the middle of the muscle —decussate at the angle of the mouth, those arising from the maxilla passing to the lower lip, and those from the mandible to the upper lip (Figure 3-9). The uppermost and lowermost fibers of the Buccinator pass across the lips from side to side without decussation.

Figure 3-9
Figure 3-9. The Orbicularis oris and its relation to other perioral muscles.

The proper fibers of the lips are oblique, and pass from the under surface of the skin to the mucous membrane, through the thickness of the lip. Finally, there are central fibers that connect the muscle with the maxilla and the septum of the nose superiorly and with the mandible inferiorly. In the upper lip, these fibers consist of the incisivus labii superioris, which arises from the alveolar border of the maxilla (opposite the side incisor tooth) and is continuous with the other muscles at the angle of the mouth, and the nasolabialis, which connects the upper lip to the back of the septum of the nose. The interval between the nasolabialis corresponds with the philtrum, which is the central depression seen on the lip beneath the nasal septum. A less complex structure, incisivus labii inferioris, is present in the lower lip and arises from the mandible to intermingle with other muscles at the angle of the mouth.

The Orbicularis oris in its ordinary action affects the direct closure of the lips. With its deep fibers, assisted by the oblique ones, it closely applies the lips to the alveolar arch. This is very important in keeping the lips in their proper position during mastication and pronunciation of words. The superficial portion, consisting principally of the decussating fibers, brings the lips together and also protrudes them forward in a “kissing” action. This pursing action of the superficial muscle fibers is what contributes to the formation of perioral rhytids or “smoker’s lines” (Figure 3-10). It is important that small doses of Botox doses are administered to these superficial fibers only, so they canavoid problems with mastication and pronunciation that may occur if the deeper Buccinator fibers are inactivated.

Figure 3-10
Figure 3-10. Contraction of the superficial muscle fibers of the Orbicularis oris contributes to the formation of perioral rhytids or “smoker’s lines.”

The Depressor Anguli Oris

The Triangularis or Depressor anguli oris arises from the oblique line of the mandible, and inserts, by a narrow fasciculus, into the angle of the mouth (Figure 3-11). At its origin, it is continuous with the Platysma; at its insertion, it is continuous with the Orbicularis oris. Contraction of this muscle over time results in melomental folds or “marionette lines” which may be treated with dermal filler agents or softened by injecting Botox directly into the Depressor anguli oris muscle at one location.

Figure 3-11
Figure 3-11. The Triangularis or Depressor anguli oris (D) arises from the oblique line of the mandible, and inserts, by a narrow fasciculus, into the angle of the mouth. (Illustration by Lauren Chavell of Medical Imagery.)

The Platysma

The Platysma is a broad sheet of muscle arising from the fascia of the Pectoralis and the Deltoid muscles. Its fibers cross the clavicle and extend obliquely and upward along the side of the neck (see Figure 3-1). The fibers then extend across the angle of the jaw and insert into the skin and subcutaneous tissue of the lower face as well as the muscles surrounding the angle and the lower part of the mouth including the Depressor anguli oris. With aging, the cervical neck skin loses its elasticity and the anterior portion of the platysmal muscle separates to form two diverging vertical bands. When the neck is animated, these bands contract and become more visible (Figure 3-12). Botox may be directly injected into these bands to reduce their appearance by weakening the force of contraction.

Figure 3-12
Figure 3-12. Contraction of the Platysma induces formation of platysmal bands that may be cosmetically undesirable. Botox may be directly injected into these bands to reduce their appearance.

Summary

In summary, it is important that physicians have a sound fund of knowledge with respect to face muscles anatomy before they implement Botox treatments into their clinical armamentarium. While this chapter provides a foundation in this regard, it is important to learn how these various muscle groups function in real life. This type of experience is best geted by taking hands-on skills transfer courses or spending time with a practitioner who regularly performs Botox injections for a variety of indications.