Area four technique: An effective injection approach to the posterior facial frame aesthetic treatment with injectable hyaluronic acid fillers

Defined as a contour line from the hairline, the zygomatic arch, to the ramus and gonial angle area of the mandible, posterior facial frame (PFF) is an important aesthetic units of the face. With the development of hyaluronic acid fillers and the improvement of injection techniques, minimally invasive injection has become one of the first options to improve PFF. However, effective and systematic injection methods to improve PFF are rarely reported in the literature.


| INTRODUC TI ON
Posterior facial frame (PFF) is one of the most important aesthetic units of the face, which can be defined as a contour line from the hairline, the zygomatic arch, to the ramus and gonial angle area of the mandible. 1 In Asian population, the PFF is often characterized by congenital temple hollowness, prominent lateral orbital rim and zygomatic arch, and poorly developed mandible profile, conveying messages of aging and depression. Moreover, aging of multiple facial layers involving bone, soft tissue, and skin exacerbates the terrible facial appearance. 2 In the past several decades, there have been multiple surgical methods to solve the problem of poor PFF, including fat grafting, zygomatic grinding, mandibular angle osteotomy, etc. [3][4][5] Postoperative complications such as surgical trauma, infection, hematoma, and long postoperative recovery period limit the promotion of these techniques.
Injectable soft tissue fillers have become a popular and widely accepted approach for facial aesthetic treatment, which represents a promising treatment approach for the PFF. 6 PFF should primarily include two aspects, to make the PFF natural and smooth, and to alleviate the slack tissue of the lateral cheek. Previous injection treatment strategies focus on one single site (e.g., nasolabial fold and temple), 7 but few researches pay attention to combination the facial lifting and volume increase of multiple facial area for poor PFF. 8 Hyaluronic acid (HA) is a natural glycosaminoglycan rich in the extracellular matrix of the connective tissue and epithelial tissue in the human body. HA was applied in the earliest use of skin improvement and was proved to have great effects on the facial remaining layers, including superficial fat, deep fat, the muscle layer, and retaining ligaments. 9,10 These broadly include correcting fine lines and wrinkles, improving skin sagging, and restoring facial volume loss. 11 An injection strategy named area four technique has been explored in our past clinical work, focusing on the four anatomical areas of PFF: anterior temporal, posterior temporal, lateral cheek, and mandibular margin. This study aims to investigate the safety and efficacy of the area four technique in the treatment of poor PFF with HA.

| Patients
All patients provided written informed consent, and the study followed the principles outlined in the Declaration of Helsinki and in conformity to regional laws and good clinical practice for studies in human subjects. Between January 2021 and January 2022, a singlecenter, retrospective study was conducted with 234 patients between 30 and 65 years old who underwent area four injection for the poor PFF. Patients with available long-term follow-up records were included. Patient records were retrospectively analyzed and anonymized for further statistical processing. The efficacy and safety of area four injection were evaluated by preoperative and postoperative image comparison. The exclusion criteria were as followed: patients also carried out improvement projects such as photoelectric tightening or wire carving within 3 months after injection. The total sample consisted of n = 187 females (mean age 38.21 ± 9.2 years) and n = 13 males (mean age 42.5 ± 7.6 years).
According to the different facial features before injection, 200 patients were evaluated and classified into four types (Type I-IV).
Type I showed a significant temple depression and visible lateral orbital margin, accompanied by sagging of the midface. Type II was characterized by cheek depression with the laxity of the anterior cheek. Type III features a combination of Type I and Type II. Type IV had the jaw angle dysplasia on the basis of the three types mentioned above, with an accumulation of perioral tissue ( Figure 1).

F I G U R E 1 Facial features of different PFF (A)
. Type I shows a significant temple depression and visible lateral orbital margin, accompanied by sagging of the midface. Type II is characterized by cheek depression with the laxity of the anterior cheek. Type III features a combination of Type I and Type II. Type IV has the jaw angle dysplasia on the basis of the three types mentioned above, with an accumulation of perioral tissue. The proportion of PFF occupied by different types (B).

| Injection procedures
Each patient received HA (Hyalumatrix, Qisheng Biotech. Ltd.) injection therapy using the area four injection method at the PFF area ( Figure 2). Hyalumatrix is a linear, homogeneous and nongranular structured sodium hyaluronate gel produced by the special process, which shows good biocompatibility, cohesion, supporting plasticity ability, deformation, and memory ability. Hyalumatrix has a hyalu-

| Parameters evaluated
Nine-item aesthetic assessment scores were reviewed on images in patients' medical records before and 1 and 3 months after treatment. The images included frontal, 45 degrees lateral, and direct lateral view, and the same images were captured after each treatment.
The images were evaluated retrospectively by the patient (Item 1) and two independent observers (Item 2-9) with experience in aesthetic medicine. The standards for evaluation were as follows: 1. Global aesthetic improvement scale (GAIS) 12

| Analytic methods
All scores were evaluated retrospectively based on previous images in individual medical record. In a blinded assessment sheet, the values for each score and each treatment were recorded.

| Classification of posterior facial frame
Of the 200 patients included in the study, Type I and Type II accounts for 27.5% and 21.5%, respectively, and Type III accounts for 46% and Type IV accounts for only 5.0% (Figure 1). Within 3 months of follow-up, 13 patients (6.5%) claimed minor postoperative bruising, which subsided within 2 weeks without any treatment. One hundred and eighty-two patients (91%) complained of discomfort while chewing and mild swelling pain in the temple and usually recovered within 2 weeks. Signs of infection, hematoma, acute vascular events, or foreign body sensations were not observed.

| GAIS results
The treatment effect of patients was evaluated using GAIS ranging from 1 (exceptional improvement) to 5 (worsening of the condition).
GAIS levels of all patients were recorded after 1 and 3 months from the treatment. Based on the results of the follow-ups, no one complained of worsen effect after treatment. Patients' profile was remarkably improved for 88% of total number of subjects 1 month after injection (35.5% showed exceptional improvement and 52.5% showed moderate improvement). The percentage of patients with exceptional and moderate improvement was increased to 89% after 3 months ( Table 2). The results demonstrate that after 3 months patients were still very satisfied with the procedure confirming the great long-lasting results by HA filler using area four technology (Figure 3).

| Absolute value of each facial aesthetic subunit score
The treatment for PFF resulted in a statistically significant improve-

| DISCUSS ION
Improving the outer contour of the face by injection is a safe and effective way, which can avoid the postoperative complications caused by surgery. 13

Score 3 months after injection mean (SD)
Temple hollowing (0-4, best-worst) 3 Step 3: subdermal cheek lifting (1 mL total) C1 Hyalumatrix 0.5 0.5 Step 4: the injection into the mandible (3 mL total) includes the true ligaments and the superficial muscular aponeurotic system (SMAS). 15 The major true ligaments of the face include the infraorbital ligament, zygomatic ligament, masseteric ligament, and mandibular ligament. 16 SMAS spreads throughout the head and neck, including the frontalis muscle in the forehead, the temporoparietal fascia in the temporal region, the SMAS in the midface, and the platysma in the neck. 17

| CON CLUS ION
Based on the results of the facial application of the area four technology, we can conclude that the procedure is safe and effective.
The area four technology has an beneficial effect on face lifting and improvement of the contour curve.

AUTH O R CO NTR I B UTI O N S
Xi Chen designed the study and wrote the paper and edited the pictures. Yipin Xu and Zhigang Xiao collected and analyzed the data.
Mei Li and Guangpeng Liu provided the injection site of the area four technique and reviewed the article.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

E TH I C S S TATEM ENT
This study (retrospective data analysis) was conducted in accordance with regional laws (China) and good clinical practice. All participants provided written informed consent. Patients unwilling to provide access to their medical records were not included in this analysis.The guidelines of the Declaration of Helsinki were followed throughout.

I N FO R M ED CO N S ENT
All of participants were signed written consent forms and known detailed information about the area four injection treatment. All

D ECL A R ATI O N S
The authors report no financial and personal relationships with other people or organizations that could inappropriately influence the work.

H U M A N A N D A N I M A L R I G HT S
This article does not contain any studies with human participants or animals performed by any of the authors.