Use of nasal septal bone to straighten septal L- Strut in correction of east Asian short nose: A retrospective study

Background: The perpendicular plate of ethmoid (PPE) was used to correct short noses in rhinoplasty in Asians, but the safe harvest of the plate and the assessment of its clinical application has been perplexing to plastic surgeons. Aims: To explore how to safely cut the perpendicular plate of ethmoid bone and evaluate its application effect. Patients/Methods: A finite element model was established to guide the clinical operation. A total of 30 patients with short noses were selected. Among them, 15 patients used autologous septal cartilage to lengthen the nasal tip, and 15 patients used the PPE to strengthen the L- shape nasal septum. The differences in the esthetic parameters


| INTRODUC TI ON
The nose is the most prominent organ of the face that reflects the three-dimensional (3D) sense of facial contours. 1 Due to ethnic factors or other influences, a proportion of Asians have a flat dorsum and hypertrophic nasal tip, and the tip projection is insufficient, which leads to the appearance of short nose deformities. 2,3 Thus, people yearn for a satisfactory nose through rhinoplasty. The graft-assisted extension of the nasal septum can adjust the height and length of the nasal tip and is widely used for rhinoplasty. 4,5 However, the septal cartilage of the East Asian population has a soft texture and is usually thin, making it difficult to provide ideal mechanical support for the nasal tip. In order to construct a long-term stable stent, plastic surgeons use autologous costal cartilage as a material for Asian nasal tip shaping. However, some patients refuse this method due to scarring caused by additional chest incisions, and the calcification of costal cartilage also limits its application. 6,7 When the volume of the septal cartilage is small, the costal cartilage is calcified, or if the patients refuse to harvest the costal cartilage, the surgeons can choose the septal cartilage combined with the perpendicular plate of ethmoid to reconstruct the nasal support structure. [7][8][9] In traditional surgery, the septal cartilage and perpendicular plate of ethmoid are cut blindly and can only be harvested based on personal experience and sensation. The whole nasal septal cartilage and perpendicular plate of ethmoid of demand size might not be cut, which might cause bleeding that is difficult to stop because of visual field problems, especially for the high position and the deep part. Coupled with unique anatomical factors, severe complications such as cerebrospinal fluid leakage may occur. 10,11 How to correctly choose the right site to cut the perpendicular plate of ethmoid so as not to damage the skull base and the selection of incision is the key in the field of short nose correction. In this study, 3D modeling and finite element simulation software were used to establish an accurate finite element analysis model, and objective biomechanical analysis was used to explore the impact on the skull base when cutting the perpendicular plate of ethmoid at different positions. Aims of the study are to explore a suitable anatomical site to achieve safe separation and accurate cutting of septal cartilage and perpendicular plate of ethmoid; also, its clinical application was evaluated.

| Finite element analysis
In previous study, 12 the craniofacial images of 104 patients were scanned using computed tomography (CT) ( Figure 1A and Figure 1B).
According to the 3D reconstruction, the geometric model of the perpendicular plate of ethmoid was established using Unigraphics NX 10.0 (Siemens PLM Software, Co., Ltd.) ( Figure 1C and Figure 1D).
The established model was imported into the ANSYS software (ANSYS Inc.) ( Figure 1E). The upper, middle, and lower parts of the perpendicular plate of ethmoid bone were cut, respectively ( Figure 1F). The contact site between the upper end of the perpendicular plate of ethmoid and the skull base was the selected site to measure the stress (additional internal forces per unit area) value.

| Participants
A retrospective study was performed on patients with short noses who underwent comprehensive rhinoplasty between January 1, 2017, and June 30, 2021. The experimental group used the perpendicular plate of ethmoid as a graft to strengthen the nasal septum, while the control group did not use the perpendicular plate of ethmoid to strengthen the L-strut to extend the tip and dorsum of the nose.
Inclusion criteria: (1) 15-60-years-old, primary nasal surgery; (2) no residual foreign body in the nasal tissue and no organic disease in the nose; (3) no metabolic disease or vital organ dysfunction; and (4) able to accurately express the wishes.

| Surgical technique
The schematic technique of surgery was performed as follows:

| Outcome measurement
Before and after surgery, 3D photography equipment Vectra XT  SPSS 24.0 software (SPSS Inc.) was used for statistical analysis.

| Statistical analysis
The distribution of nasal parameters has been reported normally in the past, so parametric test can be used for statistical analysis.
The preoperative and postoperative 3D anthropometric data between experimental group and control group were compared by Student's t-test. The total NOSE scores, ROE scores, and the average score of the doctors were calculated. The lower ROE score reflects the more esthetic nose, and the higher NOSE score reflects the more severe symptoms of nasal obstruction. The scores of three doctors were tested using one-way ANOVA. Preoperative  Typical case 1: A female patient underwent comprehensive rhinoplasty to correct short nose deformity, since the patient's septal cartilage was weak, the removed perpendicular plate of ethmoid extended an extra part to reshape the nasal tip. The patient was satisfied with the height, length, and overall curvature of the nose ( Figure 9). Typical case 2: A female patient with exposed nostril and upward rotation of nasal tip underwent augmentation rhinoplasty using septal cartilage only. After surgery, the length of the nasal dorsum increased, the contour of the nasal tip improved, and no obvious deviation was noted in the nasal columella ( Figure 10).

| DISCUSS ION
An ideal and esthetic shape of the nasal tip is a primary factor in determining the satisfaction of the patients during rhinoplasty.
However, due to patients' anatomical characteristics, such as short septal cartilage, weak lower lateral cartilage, and thick-soft tissue, many plastic surgeons have difficulty correcting the short nose in Asians. 13 It is speculated that the L-strut on the dorsal and caudal sides must be retained to support during rhinoplasty, and most Asian studies stated the width of 15 mm is the best choice. 16 Compared to Westerners, the cartilage of Asians is weaker, and their ability to support the nasal dorsum is significantly reduced. In addition, Asians have thick, soft tissues on the nasal dorsum. According to the Western standards are adopted, the supporting power of the soft tissue may be insufficient in Asians, leading to the collapse of the nasal dorsum and resulting in secondary nasal deformity. Therefore, it is necessary to strengthen the L-strut with grafts such as auricular cartilage, nasal septal cartilage, and perpendicular plate of ethmoid.
The application of the perpendicular plate of ethmoid to rhinoplasty has only begun to develop in recent years. 8,17 It can be used to make auxiliary grafts as a scaffold in the middle of the nasal cavity, which is significant to maintaining the external shape of the nose and ensuring ventilation. 18 The upper two-thirds of the perpendicular plate of ethmoid is thick, and the lower third is thin with a distinct dividing line between the two thicknesses. Appropriate tools were used to cut the middle and lower parts along the boundary where the thickness changes that avoid the potential adverse effects on the skull base, thereby preventing the occurrence of cerebrospinal fluid leakage. 18 In this study, the common esthetic parameters of the nose were appear to be aging 19,20 . Therefore, while correcting the short nose, we also operated to fill the base of the nasal columella, which made the columellar-labial angle obtuse, offsetting the above defects.
In 2016, Tae et al. 13 reshaped the nasal tip using the perpendicular plate of ethmoid and evaluated its effect. Compared to their study, we used the same materials, but the surgical methods were slightly different, resulting in varied anthropometry. We focused on the whole nose rather than just the local part of the nasal tip.     Yixin Li involved in design, manuscript revisions, and final approval.

This work was supported by Key Clinical Projects of Peking University
Third Hospital (No. BYSYZD2019013 and No. BYSYFY2021005).

CO N FLI C T O F I NTE R E S T
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
F I G U R E 1 0 Follow-up images of a typical case in the control group. A female underwent comprehensive rhinoplasty. Preoperative frontal (A), profile (B) views, and postoperative 6-month frontal (C), profile (D) views. The patient was satisfied with the postoperative results, and the nasal appearance was close to the esthetic standard of the human nose

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 A L A PPROVA L
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

I N FO R M ED CO N S ENT
All participants provided informed consent.