# Non-Surgical Touch-Up with Hyaluronic Acid Fillers Following Facial Reconstructive Surgery
## 1 Introduction  
The use of hyaluronic acid (HA) injectable fillers has become increasingly widespread in facial recontouring and rejuvenation, with significant relevance in plastic surgery. Even with increasing popularity of facial tissue augmentation in recent years, it is not a new theory. A fat grafting technique was introduced more than a century ago [1]. Other materials, such as polymethylmethacrylate (PMMA), hydroxyapatite cement (HAC), paraffin, and silicone have been utilized with overriding limitations (e.g., toxicity and foreign body reactions) [2]. It was only in the past two decades that safe, biocompatible, non-allergenic, and injectable hyaluronic acid (HA) filler products were developed and approved by the U.S. Food and Drug Administration [3]. According to the American Society of PlasticSurgeons' 2020 statistics [4], the use of HA fillers in facial non-surgical contouring has significantly increased due to their versatility, effectiveness, and rare adverse reactions [5]. Moreover, the number of available HA injectable fillers for facial recontouring has raised dramatically in the last several years and the range of products to choose from has also been impressively expanded through innovative fillers manufacturing technologies. Different products could share the same indications, yet consist of very different physicochemical profiles [6; 7]. These features distinguish products according to functionally important aspects and have become effective ways for surgeons to select which materials are the most suitable for a given surgical need.  
Compared to surgery, they provide facial rejuvenation and aesthetic enhancement at a lower cost, with less complications, minimal downtime, and immediate results. Although HA injections are excellent tools utilized in facial cosmetic improvements, they could also be applied to treat facial deformities resulting from traumatic events, orbital and periorbital surgeries, tumor resections, congenital deformities, burns, scars, and facial palsy [8; 9; 10; 11]. Injective techniques could also be utilized for HIV-related facial lipoatrophy or progressive hemifacial atrophy [12; 13; 14; 15; 16; 17]. Although hyaluronic acid is widely used for cosmetic purposes, in the literature, little is known about this procedure in reconstructive approaches [8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19].  
Facial reconstruction is considered one of the most challenging procedures in plastic surgery; despite the refinement of current techniques, disfiguring anomalies are frequently observed postoperatively, in the form of slightly hollow scars, insufficiently marked lips, asymmetries localized in the nose, skull, midface, chin, or mandibular angle [20; 21; 22; 23; 24; 25]. Aesthetic improvement is demanded from these patients (who are usually teenagers or who have undergone many troublesome surgeries) [22; 23; 24]. Viscoelastic properties, hydrophilicity, affordability, safety, biocompatibility, effectiveness, and the non-immunogenicity of HA fillers have prompted us to use this approach in these indications. Determining the appropriate HA gel is based on multiple variables, including ease of injection, longevity, surgeon preference, and cost-effectiveness. Key variables that characterize the behavior of a hyaluronic acid-based filler (to determine the most appropriate gel for every reconstructive purpose) include cohesivity, crosslinking, and HA concentration.  
We report our experiences with to emphasize the rule of HA fillers as tools beyond aesthetic treatments in facial plastic reconstructive surgery and aesthetic medicine. HA fillers are generally used for aesthetic rejuvenation, but one potential new horizon could be their application in trauma, reconstructive, and craniofacial surgery.