The Effect of Trans-Sutural Distraction Osteogenesis on Nasal Bone, Nasal Septum, and Nasal Airway in the Treatment for Midfacial Hypoplasia in Growing Patients

Abstract

The purposes of this study were to analyze the effect of trans-sutural distraction osteogenesis (TSDO) on nasal bone, nasal septum, and nasal airway in the treatment of midfacial hypoplasia. A total of 29 growing patients with midfacial hypoplasia who underwent TSDO by a single surgeon were enrolled. The 3-dimensional measurement of nasal bone and nasal septum changes was performed using computed tomography (CT) images obtained preoperatively (T0) and postoperatively (T1). One patient was selected to establish 3-dimensional finite element models to simulate the characteristics of nasal airflow field before and after traction. After traction, the nasal bone moved forward significantly (P<0.01). The septal deviation angle was lower than that before traction (14.43±4.70 versus 16.86 ±4.59 degrees) (P<0.01). The length of the anterior and posterior margin of the vomer increased by 21.4% (P<0.01) and 27.6% (P<0.01), respectively, after TSDO. The length of the posterior margin of the perpendicular plate of ethmoid increased (P<0.05). The length of the posterior inferior and the posterior superior margin of the nasal septum cartilage increased (P<0.01) after traction. The cross-sectional area of nasal airway on the deviated side of nasal septum increased by 23.0% after traction (P<0.05). The analysis of nasal airflow field showed that the pressure and velocity of nasal airflow and the nasal resistance decreased. In conclusion, TSDO can promote the growth of the midface, especially nasal septum, and increase the nasal space. Furthermore, TSDO is conductive to improve nasal septum deviation and decrease nasal airway resistance.

Midfacial hypoplasia is a craniomaxillofacial malformation caused by congenital or acquired factors, often associated with Apert syndrome, Crouzon syndrome, and other genetic diseases, and also seen in cleft lip and palate.^1,2 Midfacial hypoplasia can cause narrow maxillary dental arch, depression of the midface, and class III malocclusion.³ Some patients may also have nasal septum deflection (NSD) and airway stenosis.⁴ The nasal septum is composed of vomer, perpendicular plate of ethmoid bone (PPE) and nasal septum cartilage (SC). The nasal septal cartilage is the growth center in the midface, promoting the forward and downward growth of the midfacial bone.^5–7 Nasal septum deflection causes airway stenosis and asymmetry, which is related to nasal congestion, epistaxis, sinusitis, sleep apnea, and headache.⁸

Clinically, there are 3 main surgical treatments for midfacial hypoplasia: traditional orthognathic surgery, distraction osteogenesis (DO) with Le Fort osteotomy and trans-sutural distraction osteogenesis (TSDO).^9,10 Among them, TSDO applies force to the growing cranial suture and facial suture and induces the formation of new bone around the suture, which changes the shape and position of craniomaxillofacial bone, with the advantages of less trauma and fewer complications.¹¹ It is worth noting that the nasal septal cartilage is sensitive to the traction force, and the 3-dimensional growth of the midfacial bone can remove the space restriction on the nasal septal growth, which promotes the growth of the nasal septal cartilage.¹² Previous studies mainly focused on the effect of TSDO on the 3-dimensional growth of maxilla, while there was no report on the effect of TSDO on the nasal bone, nasal septum, and nasal airway.

Therefore, this study established 3-dimensional (3D) models of skull and finite element models of nasal airway by using the cranial computed tomography (CT) data before and after traction, aiming to analyze the effect of TSDO on the morphologic changes of the nasal bone and nasal septum and the characteristics of nasal airflow in patients with facial middle dysplasia. So as to explore the mechanism of TSDO, optimize its key technical scheme, and provide further guidance for clinical practice.

METHODS

Subjects

This retrospective study considered all growing patients with midfacial hypoplasia who were treated with TSDO from January 2005 to May 2022 at the Plastic Surgery Hospital, Chinese Academy of Medical Science and the Peking University Third Hospital. The inclusion criteria of subjects were as follows: presence with midfacial hypoplasia; under 18 years old; underwent TSDO by the same surgeon; complete traction process records; complete skull CT data before and after traction. The exclusion criteria for subjects were as follows: serious complications occurred during traction; the traction device needs to be removed in advance for some reasons; incomplete or poor-quality CT data records.

Ethical Approval

This study was conducted in accordance with the principles outlined in the Declaration of Helsinki and was approved by the Peking University Third Hospital (approval No. LA2019177). Written informed consent was obtained from the guardians of patients aged below 18 years. There were no images in which specific patients could be identified.

Surgery

The distraction system, surgical method, and specific distraction protocol had been previously described in detail by Tong et al.¹⁰ Briefly, the distraction system consisted of a rigid external distractor (RED, Cibei Medical Treatment Appliance Co., Ningbo, China), nickel-titanium shape memory alloy spring and bone-borne traction hooks (GEE Co., Beijing, China) (Fig. 1). Surgical method is as described previously.

FIGURE 1.

The distraction system consists of a rigid external distractor, nickel-titanium shape memory alloy spring, and bone-borne traction hooks.

A hole was drilled on each side of the lateral pyriform rim. Two independent traction hooks were introduced through the hole, with the head end around the canine pillars as bone anchorage and the caudal ends extending out from the nostril base. The cranial frame of RED was installed, and the spring was then used to connect the hooks to RED. The initial distraction direction was adjusted 20–30 degrees anteroinferiorly.

Data Acquisition

The skull CT images were obtained preoperatively (T0) and within 1 week after the devices were removed (T1). Scanning range: skull top to submandibular. Scanning machine: 64 row spiral CT (Aquilion 64, Toshiba Medical Systems Corporation, Japan; SIEMENS/SOMATOM Definition Flash, German). Reconstruction layer thickness: Aquilion 64: 0.625 mm. SIEMENS: 0.75 mm. After scanning, CT data were stored in Digital Imaging and Communications in Medicine (DICOM) format.

Creation and Superimposition of 3-Dimensional Models

The CT data were imported into the software Mimics Research 20.0 (Materialise, Leuven, Belgium) to reconstruct the 3D model of skull bones. The bone models of the same patient were then superimposed using the STL global registration function of the software (T0 was green, T1 was red).

Landmarks and Measurements of Variables

The bony landmarks used for creating reference planes included the following points: sella (S), basion (Ba), orbitale (Or), and porion (Po) (Supplementary Digital Content Table 1, Supplemental Digital Content 1, http://links.lww.com/SCS/F127, Fig. 2). The Frankfort horizontal plane (FH plane) was defined as the plane that passed through the bilateral Po and Or. The horizontal reference plane (HR plane) was defined as the plane parallel to the FH plane passing through Ba. The midsagittal reference plane (MSR plane) was defined as the plane perpendicular to the HR plane passing through Ba and S. The coronal reference plane (CR plane) was defined as the plane perpendicular to the HR and MSR plane passing through S (Fig. 2). The 3D rectangular coordinate system was established by taking Ba as the origin and 3 mutually perpendicular planes HR, CR, and MSR.

FIGURE 2.

Landmarks and 3D reference planes were used in this study. Landmarks from the frontal view (A); landmarks in the MSR plane (B); FH plane and HR plane from the lateral view (C); MSR plane and CR plane from the horizontal plane view (D). CR indicates coronal reference; FH, Frankfort horizontal; HR, horizontal reference; MSR, midsagittal reference.

The anatomic landmarks for measurements are described and summarized in Supplementary Digital Content Table 1, Supplemental Digital Content 1, http://links.lww.com/SCS/F127 (Figs. 2, 3). For points on both sides, the suffixes “l” and “r” denote the right side and the left side, respectively. The measurement of variables are as follows:

1. The vertical distance from N, ANB, Ans, Max to CR, and MSR plane. Note: for landmarks on the left side of MSR, the distance was recorded as a positive value. For landmarks on the right side of MSR, the distance was recorded as a negative value.

2. The length of the upper (SNM-l-SNM-r丄MSR), lower (INM-l-INM-r丄MSR), and inner (N-ANB) margin of the nasal bone; the nasofrontal angle (NFA); the nasal pyramidal angle (NPA) (Fig. 4).

3. The length of the superior (Sv-Sva), inferior (Ave-Pve), anterior (Ave-Sva), and posterior (Sv-Pve) margin of the vomer (Fig. 3A). The length of the anterior superior (E-Asc), anterior inferior (Asc-SCr), posterior superior (E-Pv), and posterior inferior (Pv-SCr) margin of SC. The length of the superior (Pfs-Es), anterior superior (E-Pfs), posterior (Es-Sva), and posterior inferior (Pv-Sva) margin of PPE (Fig. 3B).

4. The septal deviation distance (L-Max). The height of nasal septum (H-NS). The septal deviation angle (SDA) (Fig. 3C).

5. The cross-sectional area of nasal airway on the deviated side of the nasal septum (S1) on the CR plane passing through the Max, and the cross-sectional area on the opposite side of the deviated septum (S2) on the CR plane passing through the Max (Fig. 3D).

FIGURE 3.

Changes of nasal septum and nasal airway before and after traction. (A); Changes of vomer before (above) and after (below) traction. After traction, the length of the anterior margin of the vomer (Sva-Ave) and the posterior margin of the vomer increased. The length of the superior margin of the vomer (Sv-Sva) decreased. (B); Changes of PPE and SC before (above) and after (below) traction. After traction, the length of the posterior margin (Es-Sva) and the posterior inferior margin (Pv-Sva) of PPE increased. The length of the posterior inferior margin (Pv-SCr) and the posterior superior margin (E-Pv) of SC increased. (C); Changes of NSD before (above) and after (below) traction. On the coronal reference plane passing through the Max, the line crossing the attachment of the cockscomb and perpendicular to the HR plane is marked as the centerline (yellow). After traction, the L-Max and the SDA decreased, and the H-NS increased. (D); Changes of the cross-sectional area of nasal airway before (above) and after (below) traction. S1 (blue): the cross-sectional area of nasal airway on the deviated side of the nasal septum on the coronal reference plane passing through the Max. S2 (yellow): the cross-sectional area on the opposite side of the deviated septum on the coronal reference plane passing through the Max. After traction, the S1 increased. H-NS: distance between the attachment of the cockscomb and the most inferior point of the bony nasal septum (green); L-Max: distance from Max to centerline (white); SDA: the included angle between the midline and the line between the attachment of the cockscomb and the Max point.

FIGURE 4.

Changes of angles related to nasal bone before and after traction. Nasofrontal angle (NFA): angle between Gla-N connection and N-ANB connection. Nasal pyramidal angle (NPA): angle between the tangent line of the left nasal bone and the tangent line of the right nasal bone on the horizontal plane at the ANB point. NFA before traction (A); NPA before traction (B); NPA before traction (C); NPA after traction (D).

Creation of Nasal Airflow Field Models

One child (12 y old, male, nasal septum deflected to the left) was selected from the subjects to construct and calculate the nasal airflow field models before and after traction.

First, the nasal airway model was reconstructed in mimics. Manually marked the nasal airway layer by layer on the CT section and reconstructed it into a 3D model, then preliminarily smoothend the model and saved it in STL format. The STL format file was imported into the software Geomagic Wrap 2017 (Raindrop Geomagic, Durham, North Carolina) for precise surface processing and exported in ICES format. ICES format file was imported into the software ICEM CFD (ANSYS, Pittsburgh, Pennsylvania), divided into finite element meshes from global and local and exported in MSH format (Fig. 5). The MSH format file was imported into the software Fluent 16.0 (ANSYS, Pittsburgh, PA), and the nasal airflow field was calculated by the viscous fluid motion equation Navier Stokes equation.¹³

FIGURE 5.

Three-dimensional Nasal airway models. Original nasal airway model before traction (A); Original nasal airway model after traction (B); Finite element model of nasal airway before traction (C); Finite element model of nasal airway after traction (D).

The boundary conditions were as follows:

1. The nasal cavity wall was set as rigid and no-slip boundary.

2. The nostril was set as the airflow inlet with 1 standard atmospheric pressure.

3. The nasopharynx was set as airflow outlet.

According to the respiratory parameters of children,¹⁴ the tidal volume was set to 350 mL, and the ventilation volume was set to 7 L/min. The respiratory cycle was set as 3 seconds, with the respiratory wave simulated as a sine curve. The nasopharyngeal airway area of the model was obtained, and the average velocity of the airflow outlet was calculated. The Fluent results were imported into the software CFD-POST (ANSYS, Pittsburgh, PA) for postprocessing of the airflow field in the inspiratory phase to obtain the velocity streamline map, pressure contour, and velocity contour. Calculated the nasal resistance value according to the formula: $R=\Delta P/Q.$

Note: R: nasal resistance; ΔP: pressure difference between front and rear of nasal cavity; Q: gas flow rate.

Statistical Analysis

SPSS Statistics 26.0 software (SPSS Inc., Chicago, IL) was used to analyze the data. Mean ± SD was used for statistical description, and t test was used for comparison between groups. P<0.05 was considered statistically significant.

RESULTS

Patients

According to the inclusion criteria and exclusion criteria, 29 subjects were collected (Supplementary Digital Content Table 2, Supplemental Digital Content 1, http://links.lww.com/SCS/F127), including 4 female patients and 25 male patients. The age range of children before traction was 5 to 15 years, with an average age of 11.10±2.33 years. The nasal septum deviated to the right in 13 cases and to the left in 16 cases. The maximum traction force on one side is 3 to 6 kg, with an average of 4.36±0.78 kg. The duration of the traction period is 24 to 60 days, with an average duration of 40.38±7.95 days.

Morphologic Changes Before and After Traction

By superimposing the 3D bone models before and after traction, we directly compared the changes in each part of the bones. The upper end of the nasal bone moved less, while the lower end of the nasal bone moved forward more with progressively increased advancement along the midface segment and decreased nose frontal angle (Fig. 6A). The posterior part of maxilla and zygomatic arch were stretched forward and lengthened with new bone formation (Fig. 6A). On the MSR plane, it was observed that the hard palate rotated downward with Ans as the apex (Fig. 6B). The length of the posterior edge of the vomer increased. The anterior wall of the sphenoid sinus grew and expanded forward and downward (Fig. 6B). While the bone was moving forward, its own morphology was being changed as well. The nasal dorsum became widened and flattened, and the transverse diameter of the piriform aperture increased (Fig. 6C).

FIGURE 6.

Superimposition images of T0 (green) and T1 (red). The lateral view (A); the MSR plane view (B); the frontal view (C).

Comparison of the Measurements of Variables Before and After Traction

Vertical Distance From Measuring Landmarks to the 3-Dimensional Plane

For the nasal bone and the piriform aperture, the distance between the bone landmarks and the CR plane increased after traction, representing a significant forward displacement in the sagittal direction. Among them, the forward displacement at N was the least (2.04±1.59 mm, P<0.01), whereas the maximum forward displacement at Ans was 10.08±5.00 mm (P<0.001), showing a trend of increasing with the closer to the traction bearing center. Max also moved forward 5.51±7.12 mm (P<0.001) (Supplementary Digital Content Table 3, Supplemental Digital Content 1, http://links.lww.com/SCS/F127).

In the transverse direction, the distance between INM-l, INM-r, LPA-l, LPA-r, and MSR plane increased significantly after traction, which was corresponding to the widening of the lower end of the nasal bone and the widening of the piriform aperture observed morphologically. SNM-l moved slightly to the outside. Max moved slightly to the MSR plane. The other data had no significant changes (Supplementary Digital Content Table 3, Supplemental Digital Content 1, http://links.lww.com/SCS/F127).

Measurement of Nasal Bone Morphology

Compared with that before traction, there was no significant change in the length of the upper margin of the nasal bone (SNM-l-SNM-r丄MSR). The length of the lower margin of the nasal bone (INM-l-INM-r丄MSR) increased by 23.7% (P<0.01). The length of the inner margin of the nasal bone (N-ANB) was shortened by 3.8% (P<0.05). The nasal frontal angle decreased by 3% (P<0.01), and the NPA increased by 32.9% (P<0.01) (Supplementary Digital Content Table 4, Supplemental Digital Content 1, http://links.lww.com/SCS/F127, Fig. 4). After traction, the lower margin of the nasal bone became wider and the bridge of the nose became higher, which was basically consistent with the results of morphologic comparison.

Measurement of Nasal Septum Morphology

Measurement of the length of vomer

After traction, the length of the anterior margin of the vomer (Sva-Ave) increased by 21.4% (P<0.01), and the posterior margin of the vomer (Sv-Pve) increased by 27.6% (P<0.01). The superior margin of the vomer (Sv-Sva) decreased by 5.4% (P<0.05). There was no significant change in the inferior margin of the vomer (Ave-Pve) (P>0.05) (Supplementary Digital Content Table 4, Supplemental Digital Content 1, http://links.lww.com/SCS/F127, Fig. 3A).

Measurement of the length of PPE

After traction, the length of the posterior margin of PPE (Es-Sva) increased by 17.1% (P<0.01), and the posterior inferior margin of PPE (Pv-Sva) increased by 17.6%. The length of the anterior superior (E-Pfs) and the superior (Pfs-Es) margin of PPE had no significant changes (P>0.05) (Supplementary Digital Content Table 4, Supplemental Digital Content 1, http://links.lww.com/SCS/F127, Fig. 3B).

Measurement of the length of nasal septal cartilage

After traction, the length of the posterior inferior margin of SC (Pv-SCr) increased by 8.3% (P<0.01), and the posterior superior margin of SC (E-Pv) increased by 7.3% (P<0.01). The length of the anterior superior margin (E-Asc) and the anterior inferior margin (Asc-SCr) of SC had no significant changes (P>0.05) (Supplementary Digital Content Table 4, Supplemental Digital Content 1, http://links.lww.com/SCS/F127, Fig. 3B).

Measurement of NSD

After traction, the L-Max decreased by 7.1% (P<0.05) and the SDA decreased by 14.4% (P<0.01). The patients were divided into 3 groups according to the degree of SDA: mild (0–9 degrees), moderate (10–15 degrees), and severe (>15 degrees).¹⁵ Before traction, the patients included 1 case of mild, 8 cases of moderate, and 20 cases of severe with an average SDA of 16.8±4.52 degrees.

After traction, the patients included 5 cases of mild, 13 cases of moderate, and 11 cases of severe, with an average SDA of 14.43±4.70 degrees. The H-NS increased by 9.3% (P<0.01) (Supplementary Digital Content Table 4, Supplemental Digital Content 1, http://links.lww.com/SCS/F127, Fig. 3C).

Measurement of the Cross-Sectional Area of Nasal Airway

After traction, the cross-sectional area of nasal airway on the deviated side of the nasal septum (S1) increased by 23.0% (P<0.01), while the cross-sectional area on the opposite side of the deviated septum (S2) had no significant changes (P>0.05) (Fig. 3D).

Analysis of Nasal Airflow Field

The Velocity Streamline Map of Nasal Cavity

The velocity streamline map (Fig. 7A) showed that the maximum velocity and streamline concentration of bilateral nasal airflow before traction were located at the nasal limen, indicating that the nasal airflow velocity at the nasal limen was the largest. After traction, the airflow velocity of both sides of the nasal cavity at the nasal limen decreased. The symmetry of both sides increased with the decrease of streamline density on the deviated side, whereas the streamline density on the opposite side did not change significantly.

FIGURE 7.

Analysis of nasal airflow field. (A); The velocity streamline map before (above) and after (below) traction. (B); The overall nasal cavity pressure map before (above) and after (below) traction. (C); The pressure contour of coronal view (nasal limen position) before (above) and after (below) traction. (D); The velocity contour of coronal view (nasal limen position) before (above) and after (below) traction.

Changes in Nasal Cavity Pressure and Airflow Velocity

The overall nasal cavity pressure map (Fig. 7B) showed that the pressure of the nasal airway from the nostril to the nasopharynx decreased gradually, presenting the fastest downward trend near the nasal limen. The pressure of nasal cavity decreased after traction, showing a more uniform and slower downward trend from front to back. The pressure contour of coronal view (nasal limen position) showed that the pressure on the deviated side significantly decreased after traction (Fig. 7C).

The velocity contour of coronal view (nasal limen position) of the nasal cavity showed that the maximum airflow velocity was at the nasal limen. The airflow velocity on the deviated side significantly decreased after traction (Fig. 7D).

Nasal Resistance

According to the formula, the nasal resistance was 2.19×10⁻²Pa·s/mL before traction and 1.05×10^-2Pa·s/mL after traction, with a decrease of 52.05%.

DISCUSSION

The growth of midfacial bone and nasal septum interact. The midfacial bone dysplasia will bring space restrictions to the growth of nasal septum, and the growth and development disorder of nasal septum can cause midfacial depression or asymmetry.^6,7,16,17 Patients with midfacial hypoplasia usually showed midfacial depression, low and flat bridge of the nose, disorder of occlusion, stenosis of the dental arc, etc.¹⁰ Clinically, midfacial hypoplasia is often accompanied by nasal septum deviation, which is usually relieved after TSDO. TSDO allows the advancement of the midfacial skeleton to achieve occlusal correction and facial harmony through the mechanism of both suture osteogenesis and bone remodeling.¹⁸ Previous studies on TSDO mainly focused on the influence on 3D growth of maxilla, while the changes of nasal bone, nasal septum, and nasal airway after traction have not been reported. Therefore, we established 3D models and finite element models to carry out a digital anatomic study on the effect of TSDO on the nasal bone, nasal septum, and nasal airway.

The principle of TSDO is to apply distractive force to the growing bone sutures, utilizing the growth potential of the sutures to achieve changes in the position of the bones. Adolescence is generally the period of active suture growth.^19,20 In the clinical practice, we found that younger patients require less traction force during the TSDO and have shorter distraction periods, while with increasing age of the patients, the force and duration of traction required for distraction tend to increase, indicating a positive correlation between age and traction difficulty.¹⁰ Therefore, age is a major consideration. According to our experience, the distraction process of patients over 16 years old was more difficult, and the treatment effect was unsatisfactory. However, due to the need for a rigid external distractor to be fixed on the head, young children have poor compliance, and the device is prone to loosening due to collisions, resulting in distraction termination. Therefore, this technique has not been attempted in patients under 5 years of age. Considering these factors, we selected patients with midfacial hypoplasia aged 5 to 16 years for TSDO. In addition, since TSDO can apply different traction forces to the bilateral midfacial bones and adjust them dynamically based on the degree of midfacial retrusion, it is more suitable for patients with severe facial asymmetry. This technique has played an important role in correcting facial asymmetry, improving deviated nasal septum, and promoting nasal septum growth.

The nasal bone and piriform aperture are the main skeletal factors that form the actual shape of the nose.^21,22 Our research data show that after traction, the nasal bone and piriform aperture move forward significantly compared with that before surgery, with the trend of displacement increasing as they closer to the pressure point. The piriform aperture showed the largest amount of forward displacement (10.08±5.00 mm). Recent reports on the application of 3D finite element model analysis to simulate stress distribution on the skull surface under traction suggest that Von Mises stress in the paranasal area adjacent to the pyriform aperture of the piriform aperture is the largest,²³ which is also consistent with our research results.

The nasal septum is composed of vomer, PPE bone, and nasal SC, which play an important role in the development of nasal bone and maxilla.⁶ The nasal septal cartilage promotes the growth of facial bone through the growth of mesenchymal cartilage and the endochondral ossification of the area connecting with the surrounding bone, which is the growth center in the middle of the face.^5,6,24 In this study, the length of the anterior and the posterior margin of the vomer increased, showing a trend of growth forward and downward. Combined with the increase of H-NS and the changes of nasal bone morphology, the increasing length of the posterior margin of SC and PPE showed that the TSDO promoted the growth of nasal septum in the coronal direction and let to the overall height change. Also, the changes of the posterior superior margin of SC implied that the TSDO promoted the growth of nasal septum in the sagittal direction. The patients in this study were in growth period, which was also the peak growth period of nasal septal cartilage.⁶ Therefore, it is speculated that under the stimulation of traction, chondrocytes in the junction area between SC and PPE proliferate and ossify and/or mesenchymal cells in the periethmoid sutures area differentiate to bone, resulting in higher nasal dorsal height and sagittal growth of nasal septum and maxilla.

For patients with midfacial dysplasia, the relatively small sagittal skeletal framework restricts the growth of nasal septal cartilage, leading to NSD and airway stenosis, causing aerodynamic changes in the nasal cavity, and affecting respiratory function.^17,25–27 The NSD can be corrected by septoplasty.²⁸ However, it has been controversial to perform septoplasty on growing patients: nasal SC has a growth peak in adolescence, which may cause postoperative redeflection; in addition, partial excision of growing cartilage will affect midfacial growth, resulting in saddle nose deformity, midfacial hypoplasia, and malocclusion.^5,6 Our study is aimed at children in the growing period, with an average age of 11.10±2.33 years. However, septoplasty performed in patients under the age of 14 years carries a significant risk for the need for revision surgery.²⁹ Therefore, septoplasty for such children should be highly cautious.

In previous studies, it was found that surgery to correct midfacial dysplasia may affect the nasal septum and nasal airway. Traditional Le Fort osteotomy can increase the nasal airway volume and reduce the total nasal resistance,³⁰ but is associated with a risk of nasal septum perforation.³¹ Le Fort I-DO can also increase the nasal also airway volume.³² These studies suggest that surgery to correct midfacial dysplasia can play a role in improving nasal airway stenosis, which is similar to our findings. In terms of NSD, several studies showed that the traditional Le Fort osteotomy has no significant impact on NSD,^33–35 while Sung Woon reported that Le Fort osteotomy worsened NSD due to impingement between the anterior part of the cartilaginous septum and the nasal crest when the maxilla moves forward.³⁶

In our study, we described it for the first time that TSDO increased the nasal airway area and improved the NSD while correcting midfacial hypoplasia. TSDO promoted a large amount of forward movement of the maxilla and removed the limitation of nasal septum growth space due to 3D growth of the midface and the increase of the anteroposterior diameters of the nasal cavity. Thus, the curved PPE and the nasal SC released stress and reduced the curvature. At the same time, the intact nasal septal cartilage grew and remolded under the action of traction force. Computational fluid dynamics showed that the airway pressure and airflow velocity at the deviated side of nasal septum of patients after surgery decreased, the symmetry of bilateral nasal cavities increased, and nasal resistance decreased, which may further improve the quality of life of patients.

It is important to note that, despite a 14.4% decrease in SDA and a 45% reduction in severe NSD patients after TSDO, a majority of patients still experience moderate to severe NSD after surgery. The interventions after TSDO include night-time facemask therapy for maxillary protraction and orthodontic treatment to establish the correct bite relationship.³⁷ Since our treatment is mainly to promote the development of the midfacial, these postoperative measures are mainly to prevent maxillary retraction. We think these interventions can provide space for the further growth of the nasal septum, while the specific treatment effect needs to be confirmed by further research. It has been generally accepted that surgery on the nasal septum is justified when patients has reached the age of 16 years.³⁸ And the safety of rhinoplasty in teenagers has been verified.³⁹ For late adolescent patients, it is a feasible option to perform open septorhinoplasty or rhinoplasty after TSDO when their bones have matured, and the specific operation plan warrants further study.

The study lacked long-term observation and analysis of the development of nasal bone, nasal septum, and nasal airway, requiring longer clinical observation periods and long-term follow-up. Furthermore, the number of cases in this study is small, larger sample size is needed to obtain more reliable results. Finally, the data of this study lacked a clinical evaluation of nasal ventilation-related symptoms such as nasal obstruction. The Nasal Obstruction Symptom Evaluation scale and objective endoscopic examination should be added to assess the outcomes in the follow-up clinical research.

In conclusion, TSDO can promote the growth of the midface, especially nasal septum, and increase the nasal space. Furthermore, TSDO is conductive to improve nasal septum deviation and decrease nasal airway resistance.

Supplementary Material

scs-34-1971-s001.docx ^{(30.9KB, docx)}