INTRODUCTION
Dermal fillers are commonly used for aesthetic lip augmentation procedures performed to increase lip fullness, define lips, and restore volume loss that may occur with aging.1 Fillers and implants that have been commonly used in clinical practice include autologous implants (eg, fat transfer), collagens (eg, bovine, human), biosynthetic implants (eg, polymethylmethacrylate microspheres in a carrier gel, expanded tetrafluoroethylene), and cross-linked hyaluronic acid gels, such as small gel particle hyaluronic acid (SGP-HA; Restylane®, Medicis Aesthetics, a Division of Valeant Pharmaceuticals).2,3 SGP-HA is derived from a nonanimal source, does not elicit an immunogenic or inflammatory response, and is composed of small gel particles (~300 µm in diameter) stabilized with a low degree of cross-linking that provides durability of tissue support and ease of injection through small-diameter needles.4-6 Moreover, the viscous and elastic properties of SGP-HA impart pliability and moldability to the gel, providing the desired lift and definition to the lips, which may be important for achieving an optimal aesthetic outcome with lip augmentation.7
The effectiveness of SGP-HA for lip augmentation was suggested by several case series 8-10 and an open-label pilot study11 and subsequently confirmed in a randomized controlled clinical trial.12 In the randomized controlled trial, the majority of patients injected with SGP-HA demonstrated aesthetically meaningful improvements based on the blinded evaluator score on the Medicis Lip Fullness Scale (MLFS), a validated lip assessment scale.13 Initially approved by the U.S. Food and Drug Administration (FDA) for the correction of facial wrinkles (eg, nasolabial folds), SGP-HA was recently approved for lip augmentation in patients older than 21 years.4
The techniques for injection of SGP-HA for lip augmentation have included serial puncture and linear threading, which may be antegrade or retrograde. The choice of one technique over another or a combination of techniques may be influenced by aesthetic goals and patient factors.2,10 Achieving the aesthetic goals of lip augmentation with optimal tolerability and minimal risk for adverse events (AEs) requires knowledge of lip functional anatomy and skillful application of a suitable technique (or combination of techniques) to achieve accurate placement of appropriate injection volumes. This review discusses techniques for injection of SGP-HA relative to the effectiveness and safety of this dermal filler for lip augmentation that was demonstrated in a recent pivotal randomized controlled clinical trial.12
Effectiveness of Injection Techniques
A randomized, evaluator-blinded study was performed to evaluate the effectiveness and safety of dermal filler injection techniques in patients with very thin or thin (MLFS score of 1 or 2) upper and lower lips. Details on patient demographics, inclusion and exclusion criteria, study design, and written informed consent were previously described.12
Live assessments of lip fullness were made by blinded evaluators using the 5-point MLFS12 in which a response was defined as an improvement of at least 1 point from baseline in lip fullness for the upper or lower lip. A typical outcome is illustrated in Figure 1.
Although every injection technique has the potential to achieve effective results, an analysis of the injection techniques used in this study found differences in the likelihood of achieving a positive response. In this study, most patients (54%) received more
