# Non-Surgical Touch-Up with Hyaluronic Acid Fillers Following Facial Reconstructive Surgery
## 4 Discussion
A prospective study evaluated and compared HA and autologous fat (AF) injection for reconstructive purposes in case of temporal following after lateral orbital wall decompression [80]. In this study, both injections of HA and AF are demonstrated to be safe and effective. However, a higher total volume of AF than HA was required to achieve the same soft tissue volume. HA was reported to be less time consuming because it did not involve a fat harvesting procedure [80]. Moreover, a review demonstrates the same efficacy, safety, and durability of both HA fillers and AF injections for the treatment of human immunodeficiency virus (HIV)-associated facial lipoatrophy syndrome [81]. It has become popular to use hyaluronic acid (HA)-based fillers to treat facial wrinkles and deep tissue folds [82]. Their space-filling properties are well described both clinically and histologically [83; 84; 85; 86], and multiple reports demonstrate the positive effects of HA-based fillers on the dermis [83; 84; 85; 86; 87; 88]. HA filler charming features could be related to the relative ease of application, immediate results, and minimal downtime. Because of its effectiveness, safety, and well-tolerated properties, the HA injective technique represents an attractive treatment option, using a minimally invasive technique that could be performed at the office. Thus, facial reconstruction using HA has many advantages when compared to traditional techniques. One outstanding perspective of HA filler injection could be its applications in the reconstructive field. This technique could be applied in any area with a lack of tissue resulting from trauma, tumor resection, and postoperative deformities; it shows immediate, improved visual results, with high patient satisfaction. Therefore, HA fillers have a high level of aesthetic and functional results in a non-invasive way, with a simultaneous increase of volume and flexibility, without the necessity of a complex reconstructive surgical procedure. The fluidity of HA fillers allows for great precision during injection, which could be performed superficially in a subcutaneous layer as well as deep to the bone, with a restoration in facial projection, such as in the zygomatic area or skull prominence [8]. HA injections, similar to fatty tissue transfer reconstructive outcomes, could achieve outstanding, natural, and symmetrical aesthetical results, with the advantage of avoiding surgical procedures or anesthesia. Moreover, HA fillers have a low adverse event profile, because of the existence of an antidote, hyaluronidase [89; 90; 91; 92; 93; 94; 95]. In fact, a unique characteristic of HA is its reversibility via enzymatic digestion with hyaluronidase, a naturally occurring FDA-approved enzyme as a drug dispersion agent. HA filler degradability by hyaluronidase could be considered a safety-feature, giving HA filler a potential edge over other filler materials [91]. Injection technique related-complications, such as overfilling or misplacement, could be reversed by hyaluronidase injection. Nodules, visible or palpable irregularities, occur in only 0.01-0.1% of the cases, and have been attributed to hypersensitivity, foreign body reactions, injection placements, infections, and biofilm development [96; 97]. In case of vascular complications, such as impending necrosis or visual loss, the HA filler is unique, in that it can be dissolved with hyaluronidase injections, enhancing its paramount safety features. Because of the varying biochemical properties of the different HA fillers, it should be underlined that each injectable may have a different sensibility to hyaluronidase [95]. Naturally occurring HA degrades with a half-life of 12-24 h while exogenous HA has a half-life of 1-2 h [98]. Therefore, the manufacturing aim is to create an HA filler with increased tissue residency and elasticity, maintaining its biocompatibility. Studies have highlighted that HA content, cohesivity, and crosslinking properties may play a role in the sensitivity and degradability of these fillers to enzymatic degradation [84].