Masseter Muscle and Mid-Pupillary Line

The masseter muscle is a good starting point. It is the large muscle of mastication that occupies the lateral portion of the cheek below the zygomatic arch (Figure 1.1). The parotid gland rests on this muscle. At its anterior border on a line drawn from the tragus to the middle of the upper cutaneous lip, the parotid duct can be identified as it dips inward piercing the buccinator muscle to open into the mouth at the level of the second upper molar. Also, at the jaw line, just at the anterior border of the lower masseter muscle, the facial artery and vein enter onto the face. Pulsation of the artery is often possible at this location. The superficial temporalis artery pulse can be felt just anterior to the ear at its superior attachment. Just beyond this it splits into superior and parietal branches.

Figure 1.1 Surface landmarks based on the masseter muscle.

The mid-pupillary line is identified with the patient sitting up and gazing straight ahead. Three important openings in the skull can be located (Figure 1.2). The superior orbital foramen is located at the superior orbital rim. Through it exits the important supraorbital neurovascular complex. Similarly, the infraorbital foramen, about 1 cm below the inferior orbital rim, contains the infraorbital neurovascular artery, vein and sensory nerve. Finally, the mental foramen, located in the alveolar bone of the mandible in the mid-pupillary line, contains the mental artery, vein and nerve. The exact location of all three of these orifices is important when performing respective nerve blocks of the sensory nerves exiting them.

Figure 1.2 Surface landmarks: the mid-pupillary line.

Relaxed Skin Tension Lines (RSTL)

The lines and wrinkles that develop with age and sun exposure become an easily recognizable road map of the face. These wrinkles and creases, first noted as hyperanimation smile lines or frown (scowl) lines, may become permanently etched as elastic tissue degenerates and becomes ineffective in resisting the pull of the underlying muscles of facial expression. These are referred to as the relaxed skin tension lines (RSTL) (Figure 1.3) and run perpendicular to the exertion of the mimetic muscles below. These lines are often the best choice for the placement of elective scar lines on the face. When they are readily apparent, no problem is posed in designing scar orientation. In younger people, having them animate by grimacing, wrinkling the forehead, smiling or puckering will usually expose the RSTL sufficiently to make the correct choice. Similarly, pinching the skin from various directions will also reveal the flow of the RSTL. Scars not oriented within or parallel to the RSTL are generally more noticeable, as they don’t go with “flow” of the region. This is especially apparent when the patient is smiling or going through some other active form of dynamic emotional expression.

Figure 1.3 Relaxed skin tension lines of the face.

Cosmetic Units and Junction Lines

One of the major conceptual advances over the past decade or so in reconstructive and aesthetic surgery is the refinement and widespread acceptance of the junction lines and cosmetic (aesthetic) units of the face (Figure 1.4). Cosmetic unit junction lines are the lines on the face at the borders of the cosmetic units. They include the well-defined melo-labial fold that separates the cheek from the lip, the mental-labial crease that divides the chin from the cutaneous lower lip, the hairline, and the jaw line. More subtle junction lines separate the cheek from the nose (nasofacial) and lower eyelid from the cheek. The nose has several subunits defined by the alar groove, the dorsal crests and the nasofacial line. Collectively, these are the outlines that caricaturists use along with exaggerated features (broad forehead, wide-set eyes, protruding nose) to rapidly define an individual’s countenance and personality. They are also the best location for camouflaging scars. Since lines and shadows are anticipated in these areas, scars tend to visually disappear when placed within them. Conversely, scars crossing junction lines are all too noticeable.

Figure 1.4 Cosmetic units and junction lines of the face.

Cosmetic units are the areas cordoned off by the junction lines. They share common characteristics of skin color and texture, pore opening size, elasticity, thickness, and presence or absence of hair. The cheek, temple, chin, and eyelids are their own well-defined units, whereas the nose, cheek, and ear can be subdivided into smaller units. The nose in particular has been defined to include the root, the dorsum, the lateral side walls, the paired alae nasi, and the tip.

Several useful principles of closure have been derived from the conceptualization scheme noted above. These include:

Free Margins: Concept of Tension Vector of Closure

Another important concept when performing facial surgery is that of the free margins; the eyebrows, eyelids, lips and nostril rims. These are important as they offer little resistance to the forces of wound closure and can be easily distorted by excess tension. This can occur from the immediate direct exertion of tension by a side-to-side closure or the delayed application of tension as a second intention healing wound or split thickness graft site contracts. The resulting asymmetries can be both cosmetically unsettling and functionally disabling. Ectropion of the lower lid can lead to permanent visual problems while eclabion and lack of a proper oral seal can cause problems with phonation and eating/drinking while looking unsightly.

The tension vector of closure can be favorably manipulated by one of several techniques:

Concavities and Convexities: Implications for Second Intention Healing

The face is not a flat structure. Rather, it is composed of undulating well-defined elevations and depressions that need to be taken into consideration when planning closures. Scar lines that traverse from convexity to concavity may contract in an unbecoming manner and may require preplanning with an S-plasty configuration for appropriate closure. However, the major effect of whether an area is flat, concave or convex determines how well defects resolve when allowed to heal by second intention. Although the size and depth of the defect have some impact on the final healing, defects on concave surfaces such as the temple, the medial canthus and the alar groove do well, whereas defects on convex surfaces such as the malar eminence, the tip of the nose and the chin generally heal poorly with webbed or elevated scars. Defects on flat surfaces, such as the forehead or cheek typically respond somewhere inbetween.

Introduction

One of the things that separates humans from other animals is the ability to communicate by use of the muscles of facial expression (the mimetic muscles). By use of this silent mode of interacting, human discourse is enriched by nuance and subtlety. Shades of annoyance, reverie, indifference, skepticism, sarcasm, etc, are molded onto the spoken word.

Muscles of facial expression are unique in that they are the only muscles to insert into the skin. They do so via fibrous septae that connect the superior portion of the muscle to the undersurface of the dermis. They also insert or interdigitate with the other mimetic muscles. So while the frontalis muscle wrinkles the forehead and raises the eyebrow, it also helps open the eye widely by partially inserting into the upper fibers of the orbicularis oculi muscle (Figure 1.6).

Figure 1.6 Muscles of facial expression. (a) Anterior view. (b) Lateral view.

Innervation of the muscles is exclusively by branches of the facial or cranial nerve VII. This occurs at the lateral undersurface of the muscle. The muscles are most effective and concentrated in the mid-plane of the face and exert their major effect around the two major orifices of the face; the eyes and the mouth. The aponeurotic component tends to be more laterally displaced on the face in the superficial musculoaponeurotic system (SMAS) of the cheek and the superficial temporalis fascia of the temple. The other major component of the aponeurotic system, the galea aponeurotica is spread over the expanse of the skull, connecting the anteriorly displaced frontalis muscle with the occipitalis muscle of the neck.

Muscles Acting around the Eyelids

The frontalis muscle is the primary muscle of the forehead and its main function is to wrinkle the skin of the forehead and elevate the eyebrow. Accordingly, it has been called the “surprise” muscle. It also, through its interdigitations with the upper fibers of the orbicularis oculi muscle, assists in opening the eye widely. Injury to the temporalis muscle results in flattening the skin of the forehead, brow ptosis, and accentuation of the effects of dermatochalasis and upper visual field gaze.

The corrugator supercilii muscle has come under intense interest recently with widespread popularity of botulinum toxin injections. The muscle originates from the frontal bone of the medial orbit in line with and just above the medial canthal tendon insertion. It has two slips; the oblique head that runs a short distance superiorly to insert into the skin of the medial eyebrow and helps depress the medial brow and the larger transverse head that runs laterally to insert widely into the skin of the eyebrow. It functions mainly to pull the eyebrow medially and slightly downward to create the vertical scowl lines of the glabella. Recently, the depressor supercilii has been described. It arises just above and deep to the corrugator supercilii and extends vertically superior to also attach into the skin of the medial eyebrow. It appears that there are three muscles that act in concert to depress the medial eyebrow: the most deeply placed depressor supercilii, the middle oblique head of the corrugator supercilii, and the vertically oriented fibers of the medial/superior orbicularis oculi muscle.

The key to the orbital region is the large, sphincter-like circumferential orbicularis oculi muscle. It has both outer orbital and inner palpebral