Key points

Introduction

Facial aging may manifest as skin texture and color changes, formation of fine lines and deeper creases, more pronounced active wrinkles, and overall facial soft tissue decent. Decreased skin tone, fat loss, and underlying bony changes contribute to the loss of facial fullness. Each of these components of facial aging can be addressed by specific treatments such as medical grade skin care and resurfacing, neuromodulators, and soft tissue fillers. Although not a substitute for surgical rejuvenation, nonsurgical options are more accepted by patients owing to convenience, lower initial cost, less downtime, and fears of “going under the knife.” In this environment, hyaluronic acid (HA) fillers have become in leading tool in not only maintaining a youthful facial appearance, but also for enhancing facial features in younger patients.

Introduction

Facial aging may manifest as skin texture and color changes, formation of fine lines and deeper creases, more pronounced active wrinkles, and overall facial soft tissue decent. Decreased skin tone, fat loss, and underlying bony changes contribute to the loss of facial fullness. Each of these components of facial aging can be addressed by specific treatments such as medical grade skin care and resurfacing, neuromodulators, and soft tissue fillers. Although not a substitute for surgical rejuvenation, nonsurgical options are more accepted by patients owing to convenience, lower initial cost, less downtime, and fears of “going under the knife.” In this environment, hyaluronic acid (HA) fillers have become in leading tool in not only maintaining a youthful facial appearance, but also for enhancing facial features in younger patients.

Hyaluronic acid filler composition

Although HA fillers may seem to be similar, they actually each have different physical properties that differentiate them, making proper product choice important when used for facial rejuvenation. Factors such as HA concentration, amount of cross-linking, particle size, extrusion force, and elastic modulus (G′) influence product selection and indications. Therefore, there is no universal HA filler. Although there is some overlap in their clinical uses, they should not be considered interchangeable in all situations.

This section highlights of a more detailed analysis of HA fillers by Kabik and colleagues. HA is found in human tissue but the injectable products are obtained from animal or bacterial sources. The HA molecule itself is a glycosaminoglycan disaccharide composed of alternately repeating units of d -glucuronic acid and N -acetyl- d -glucosamine. At physiologic pH, HA binds water extensively, providing “fullness” in the tissue. HA may be modified by chemical cross-linking between HA strands, which increases product firmness, making it more resistant to stress, and also making it more resistant to in vivo enzymatic degradation resulting in a longer duration of filler effect.

Although each product has a listed HA filler concentration, there may be variation in the amount of soluble versus insoluble HA. Because the soluble HA is metabolized rapidly, it does not contribute to clinical effectiveness. Therefore, listed HA concentrations may not truly reflect product performance.

The rheology of HA fillers is complex and laboratory measurement differences may not translate to clinical differences. However, a products’ G′ may be used to describe its firmness or ability to “lift” tissue. A high G′ product will require more applied stress to deform it, whereas a low G′ product will deform with little applied stress.

In clinical terms, low G′ HA products may be better for fine lines and wrinkles and where firmness is not desired, for example in the lips. High G′ products may be better suited for deeper tissue elevation such as moderate to severe nasolabial folds and malar enhancement. Reported G′ measurements in Pascal units are listed in ascending order :

Finally, because HAs bind water, they may result in tissue swelling after injection. This is partially dependent on HA molecule modifications and the amount of cross-linking.

Patient assessment

Proper patient assessment includes not only the area of their present concern, but an overall facial assessment and plans for future treatments. In middle-aged and older patients, HAs typically are combined with neuromodulators and medical grade skin treatments to achieve proper facial rejuvenation. Despite patient hopes, not all facial aging can be improved with fillers. A discussion of why more invasive treatments are appropriate may be needed. Likewise, expectations that 1 or 2 syringes of a product will give dramatic results will also need to be addressed. Lip enhancements may only need 1 or 2 mL of an HA, but moderate facial aging may require 1 to 2 mL in each temple, malar region, nasolabial fold, and perioral area. Eight to 10 mL of HA (or more) may be used in some patients to achieve a “liquid facelift.” If high filler volumes are being considered, other longer acting products such as l -poly-lactic acid (Sculptra) and polymethyl methacrylate (Bellafill) should be discussed. Calcium hydroxylapatite (Radiesse) is another option for deeper injections to achieve tissue elevation, such as in the malar or temple regions.

A written informed consent should be obtained before the first injection session. Standard photo documentation of the area being treated and the entire face should be done before any treatment. Because many of the changes from filler injections are subtle, consistent before and after images are important in measuring outcomes and educating patients.

Ethnic and gender considerations

Not all ethnic groups have similar needs and this should be taken into account. For example, whereas Caucasian patients may seek injections to address age-related changes, Asian patients may be younger and be seeking changes in facial shape. The “T zone” (forehead, nose, cheeks, and chin) can be projected in such cases to reshape the face. Ethnic groups with darker skin types, such as African Americans, may have fewer fine lines and wrinkles and will focus more on volume loss. Latino patients may have unique cultural considerations that can influence treatment. Men are more likely to focus on regaining stronger male features, such as in the chin, and also present for nasolabial fold and tear trough correction.

Injection preparation and technique

Depending on the injection site and size of needle used, analgesic modalities include topical anesthetics, ice packs, distraction techniques, local anesthetic injections, and nerve blocks. Some HA products are available with lidocaine mixed in the syringe, which decreases injection discomfort.

The injection site should be cleaned in a wide area with appropriate skin disinfectant. Dry iodine-based solutions can be wiped off with an alcohol pad to allow assessment of skin color for signs of blanching or intravascular injection. Technique should be as aseptic as possible because late infections and biofilm formation can occur.

For intradermal injections, short 29-G needles work well. When using a more viscous HA product, 30-G and 31-G needles can be used. For subdermal injections, longer 27-G or 29-G needles are useful. More recently, disposable blunt-tipped injection cannulas have been favored for subdermal and deeper injections because they may cause less bruising and are less likely to result in an intravascular injection.

Specific injection technique depends on the injection site, tissue plane, and clinical problem being treated. Small bolus injections (0.05–0.1 mL) are appropriate for deep and supraperiosteal injections such as for malar elevation or filling in the prejowl sulcus. Fine lines and wrinkles are best treated with smaller volume linear injections of product into the dermis, parallel to the line being injected. Elevation of more superficial tissue, such as the lip corners or cheek hollows, can be done with a cross-hatching technique of linear perpendicular injections. A fanning technique from a single injection point is useful to highlight or elevate an area. Low injection pressure and small volume injections will prevent overcorrection. If tissue swelling makes it difficult to assess the results, the injection can be stopped and repeated in 1 to 2 weeks.

After the injection, the area should be palpated to check for any lumps or unevenness, which can me massaged until smooth. Cool gel packs are useful immediately after injection to reduce swelling and bruising. Patients can resume regular activities, but should be instructed not to massage or otherwise manipulate the treatment area.

Follow-up evaluation is suggested at 2 weeks to determine if additional injections are needed. If any nodules are seen, they may still be able to be manipulated and made smooth. If an area is obviously overcorrected, or the patient is not satisfied with the results, HA fillers (unlike non-HA fillers) can be reversed with hyaluronidase. A human recombinant hyaluronidase (Hylenex, Halozyme Therapeutics) is preferable to animal derived hyaluronidase. Small amounts of HA may be dissolved with 15 to 30 units of hyaluronidase, although more may be needed (50–100 units) for larger amounts or in products with high HA cross-linking.

HA products are not intended to be stored for use after opening the syringe. However, if used under sterile conditions, they may be stored for at least 2 months without any bacterial growth.

Product composition and available products

Worldwide, there are many HA injectable products with indications for both facial aesthetic and other uses. The products mentioned below will be limited only to HA fillers approved by the US Food and Drug Administration (FDA) for facial aesthetics as of January 2016.