History

Hyaluronic acid (HA) is a naturally occurring glycosaminoglycan compound, which is highly hydrophilic, and lacks variance among dissimilar species. It forms as a largely water-soluble linear polysaccharide comprised by repeating units of N-acetylglucosamine and D-glucuronic acid. HA serves as a major structural component of extracellular space within the skin, binding water to maintain volume and viscoelasticity.

There are two categories of HAs commercially available as dermal fillers. The first is animal derived (e.g. Hylaform Gel, Genzyme Corp., Cambridge, MA), and procured from the combs of specially bred roosters, while the second is biosynthesized from fermentation cultures of Streptococcus bacteria e.g. Restylane, (Medicis, Scottsdale, AZ) and Juvaderm (Allergan Inc., Irvine, CA). Unlike collagen, species and tissue homogeny makes the potential for immunological reactions with this biopolymer significantly less likely. Skin testing is therefore not routinely performed. Regardless of how it is obtained, unbound HA undergoes rapid degradation in the body, with a typical half-life of 24 to 48 hours. To provide clinical efficacy, HA must be “stabilized” by cross-linking the molecule to maintain durability within the skin and other tissues, without compromising biocompatibility. It is by this distinctive process of cross-linking that HA develops its characteristic persistence in vivo, making it well-suited for soft tissue augmentation.

In 1996, non-animal stabilized hyaluronic acid (NASHA) was placed on the European market under the trade name Restylane and was well received due to its increased longevity over collagen fillers. In a randomized study reported in 2003, Restylane was compared to Zyplast (bovine collagen; Inamed Aesthetics, Inc. Santa Barbara, CA.). The study indicated “superiority” of Restylane over Zyplast employing the Wrinkle Severity Rating Scale (WSRS) “at all time points and at 6 months” (Narins et al., 2003). This research also demonstrated a comparable safety profile and was instrumental for FDA approval within the United States later that year. According to a statistical analysis by the American Society of Aesthetic Plastic Surgery, there were 1,593,554 HA injection procedures performed in the United States during 2006, making it the second most popular cosmetic procedure within our specialty. Currently, both NASHA as well as animal-derived HA are marketed by multiple sources throughout the world. Individual products vary in regard to particle size, concentration of HA as well as the degree of cross-linking. These attributes correlate with the product’s corrective abilities, flow characteristics, and, presumably, duration (Table 74.1).

Physical evaluation

Anatomy

Facial aging is commonly characterized by the loss of cutaneous and subcutaneous volume. This is attributable to resorption of the facial skeleton and atrophy of subcutaneous fat. In addition, there is thinning of the dermis with pronounced elastosis and a progressive reduction of HA. These factors combine to produce the aesthetically recognizable stigmata of the aged face, such as sagging and wrinkling of the skin, as well as increased prominence of the bony landmarks and vascular structures (Fig. 74.1).

Fig. 74.1 Youthful vs. aged face.

As the malar fat pads descend with age, pleats of skin and subcutaneous tissue develop and progressively gain prominence, emphasizing the nasolabial folds. Similarly, the labiomental folds or “marionette lines” form as the soft tissues of the lower face, migrate inferomedially, creating a relative sulcus in the prejowl area. Brow ptosis brings about a compensatory resting contraction of the frontalis muscle, which results in dynamic and persisting transverse rhytides of the forehead. Additionally, repeated animation of the corrugator and procerus muscles eventually give rise to the telltale vertical rhytides of the glabellar complex.

The nasojugal fold or “tear trough,” is created by a triangular gap located between the orbicularis oculi muscle and the angular head of quadratus labii superioris. These structures combine to form a depression along the orbital rim. In senescence, there is a progressive hollowing of this area created by the attachments of the orbital septum to the inferomedial aspect of the orbital rim. The effect of these anatomical changes is generally exacerbated in individuals with a congenital underdevelopment of the suborbital malar complex, and may be associated with pseudoherniation of the orbital fat pads, which serves to further highlight this defect.

As a focal point of the face, the lips, when full and well proportioned, have historically been associated with youth and sensuality. With advancing age, fat and muscular atrophy combined with bony resorption within the mandible and maxilla result in a generalized involution of the perioral structures. There is a ptosis of the commissures with increased show of the lower dentition. These features are underscored by the actions of the depressor anguli oris and depressor labii inferioris, which function to draw down the lower lip and corners of the mouth, producing a somber and uninviting appearance.

Traditionally, these anatomical changes were most commonly corrected via exclusively surgical modalities (e.g. rhytidectomy), and we truly believe the surgical facelift remains the gold standard for addressing lax and aged skin of the face. More recently, however, a “synergistic” approach addressing skin laxity and excess, as well as the loss of volume is becoming favorable. It is within this philosophy of volumetric restoration that HA fillers have found a well-defined niche. In addition, injectable therapies offer a treatment option for patients who are not candidates for, or are unwilling to undergo elective aesthetic surgery.

Technical steps

There are numerous techniques that can be used for injection of HA products. These methods vary depending upon the area being addressed, as well as the preferences of the injector. Most commonly, “serial puncture” or a “linear threading” technique are employed, especially when treating the nasolabial folds, specific rhytides or the lip border. By fully inserting the needle and injecting while it is being withdrawn, as in threading, we have the added benefit of fewer puncture sites. We often combine both methods in a “serial threading” approach, which also requires less injection points, yet allows precise placement of the filler product (Figs 74.2, 74.3). By always keeping the needle moving during injection, a smooth and predictable deposition of product is achieved.

Fig. 74.2 Serial puncture injection technique.

Fig. 74.3 Linear threading injection technique.

For larger flat areas such as the malar prominence or cheek, a “fanning” pattern of injection is often beneficial. As in threading, the needle is inserted fully, and the filler is extruded upon withdrawal. Prior to removal from the injection site, the trajectory is redirected in a radial pattern and repeated, not unlike the cannula movements in a suction lipectomy procedure. This configuration may be overlaid at 90 degrees, in a variation of the “cross-hatch” technique, providing volumization in a uniform manner (Figs 74.4, 74.5).

Fig. 74.4 Fanning pattern injection technique.

Fig. 74.5 Cross-hatch injection technique.

The most commonly treated areas for soft tissue augmentation with HA are the nasolabial folds, which is currently the only site specifically approved and labeled for injection by the FDA. This is also a reasonable area for the novice injector to gain experience in the use of HA fillers, as it is fairly forgiving. Correction is typically achieved with 1–3 mL injected bilaterally, depending upon severity. Often, there is a asymmetry in these folds, which must be addressed in the treatment plan in order to optimize results. Overcorrection, however, is discouraged, as it may produce an unnatural appearance which is accentuated with muscular contraction. It is of key importance that the product be placed in the deep dermis to avoid being visible and is injected slightly inferomedial to the folds themselves to prevent exacerbation of the deformity. An overlaid fanning technique works well in the superior aspects for this application, where the most volume is generally required (Figs 74.6–74.9).

Figs 74.6 & 74.7 Plan for injection of tear troughs, bilateral inframalar hollows and nasolabial folds in a 38-year-old woman who complains of volume deficiency of her face.

Figs 74.6 & 74.7 Plan for injection of tear troughs, bilateral inframalar hollows and nasolabial folds in a 38-year-old woman who complains of volume deficiency of her face.