Finite Element Model Analysis of Cephalic Trim on Nasal Tip Stability

Evaluating the Mechanical Strength of 3-Dimensionally Printed Implants in Septorhinoplasty through Finite Element Analysis

BACKGROUND

Autologous nasoseptal cartilage grafts are used to correct nasal asymmetry and deviation in rhinoplasty, but patients who have undergone multiple operations may have limited autologous cartilage tissue available. L-strut implants created on a 3-dimensional (3D) printer may address these challenges in the future, but their mechanical strength is understudied. Silk fibroin-gelatin (SFG), polycaprolactone (PCL), and polylactide (PLA) are bioinks known for their strength. The authors present finite element analysis (FEA) models comparing the mechanical strength of 3D-printed SFG, PCL, and PLA implants with nasoseptal cartilage grafts when autologous or allografts are not available.

METHODS

FEA models compared the stress and deformation responses of 3D-printed solid and scaffold implant replacements to cartilage. To simulate a daily force from overlying soft tissue, a unidirectional load was applied at the "keystone" region given its structural role and compared with native cartilaginous properties.

RESULTS

The 3D-printed solid SFG, PCL, and PLA and scaffold PCL and PLA models demonstrated lower deformations compared with cartilage. Solid SFG balanced strength and flexibility. The maximum stress was below all materials' yield stresses, suggesting that their deformations are unlikely permanent under a daily load.

CONCLUSIONS

The authors' FEA models suggest that 3D-printed L-strut implants carry promising mechanical strength. Solid SFG results mimicked cartilage's mechanical behavior. Thus, scaffold SFG merits further geometric optimization for potential use for cartilage substitution. The 3D-printed septal cartilage replacement implants can potentially enhance surgical management of patients who lack available donor cartilage in select settings.

CLINICAL RELEVANCE STATEMENT

Computational simulations can evaluate the strength of 3D-printed implants and their potential to replace septal cartilage in septorhinoplasty.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, V.

A Safe Technique for Excising the Perpendicular Plate of the Ethmoid Bone in Patients with Crooked Nose: A Finite Element Analysis

BACKGROUND

Correction of the crooked nose, especially the perpendicular plate of the ethmoid bone, has the potential to cause skull base injury. At present, the safe and effective method for perpendicular plate resection has not been clearly defined through biomechanics.

METHOD

CT scan data of 48 patients with crooked nose and deviated nasal septum were divided into C-type, angular deformity-type, and S-type based on the morphology of the 3D model. Different types of finite element models of the nasal bony septum and skull base were established. The osteotomy depth, angle, and force mode of the PPE resection were simulated by assembling different working conditions for the models. The von Mises stress of the anterior cranial fossa was observed.

RESULTS

When the osteotomy line length was 0.5 cm, the angle was at 30° to the Frankfurt plane, and 50 N·mm torque was applied, the von Mises stress of the skull base was minimal in the four models, showing 0.049 MPa (C-type), 0.082 MPa (S-type), 0.128 MPa (angular deformity-type), and 0.021 MPa (control model). The maximum von Mises stress values were found at the skull base when the osteotomy line was 1.5 cm, the angle was 50°, and the force was 10 N along the X-axis, showing 0.349 MPa (C-type), 0.698 MPa (S-type), 0.451 MPa (angular deformity-type), and 0.149 MPa (control model).

CONCLUSION

The use of smaller resection angle with the Frankfurt plane, conservative resection depth, and torsion force can better reduce the stress value at the skull base and reduce the risk of basicranial fracture. It is a safe and effective technique for perpendicular plate resection of the ethmoid bone in the correction of crooked nose.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Correction of Short Nose Using M-shaped Cartilage in Asian Patients: Finite Element Analysis and Recommendations for Surgery

BACKGROUND

Using M-shaped cartilage grafts is a new method for the correction of short nose deformity with good effect for Asians. Although the basic approach to M-shaped cartilage surgery is well understood, there is a great deal of uncertainty when plastic surgeons perform the procedure, and still a lack of standard guidance on the specific details.

METHODS

In this study, the authors used finite element analysis to explore and compare postoperative cartilage stability of different fixing methods, different suturing positions, and different sizes of M-shaped cartilage. The authors applied a 0.01 N load to a 1 cm2 area of the nasal tip to simulate nasal tip palpation and compared the maximum deformations of different groups, which were used to make stability judgments.

RESULTS

The maximum deformation of the model was the least when the M-shaped cartilage was fixed medially to the septal cartilage and laterally to the outer crura of the lower lateral cartilage. At the same time, the maximum deformation was the least when the M-shaped cartilage was sutured to the middle of the nasal septal cartilage. Besides, the length of M-shaped cartilage was preferably around 30 mm, while its width was not worthy of being overly concerned.

CONCLUSIONS

For optimal postoperative stability of Asian short nose correction, the M-shaped cartilage should be sutured and fixed medially to the middle of the septal cartilage and laterally to the lateral crura of the lower lateral cartilage, and the length of the M-shaped cartilage should be controlled at around 30 mm.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Effect of septal extension graft on nasal tip support: A finite element analysis

BACKGROUND

Septal extension graft (SEG) is an effective method to control the projection, rotation, and shape of the nasal tip. However, the structural mechanics of SEG have not yet been adequately determined.

OBJECTIVES

The purpose of this study was to examine the effect of SEG parameters on nasal tip support using finite element analysis.

METHODS

A multicomponent nasal model was constructed from a computed tomographic scan. A control model without graft and a total of 15 models with different SEGs were created, regarding the direction, length, width, and piece of SEG. The nasal tip compression was simulated to analyze the von Mises stress, reaction force, and strain energy of the tip structure.

RESULTS

The SEG increased the max stress, reaction force, and strain energy of the nasal tip compared to the normal control. The SEG perpendicular to the nasal dorsum resulted in the highest maximum stress, reaction force, and strain energy for the same size of SEG. With the length increasing from 15 × 8 × 1 mm to 25 × 8 × 1 mm, the reaction force remained relatively stable, but the stress on the graft reduced significantly. Adding the width and pieces of the SEG increased the reaction force and strain energy of the tip.

CONCLUSION

The placement of SEG can strengthen the nasal tip support. The direction, length, width, and piece of SEG have an impact on the mechanics.

LEVEL OF EVIDENCE

Diagnostic, III.

A comprehensive analysis of the correction of alar retraction in rhinoplasty: A systematic review

BACKGROUND

Alar retraction, as a type of alar deformity, seriously affects the esthetic perception of the nose in patients. Despite the rapid development of rhinoplasty in recent years, the treatment of alar retraction is still a challenge work in plastic surgery. This systematic review highlights the etiology, treatment, and prevention of alar retraction to further guide practitioners.

METHODS

A systematic review was conducted from 1975 to 2020 through PubMed, Embase, Web of Science, and Cochrane database with the key words "alar retraction" and "rhinoplasty" or "Rhinoplasties" to investigate the surgical treatment of alar retraction. The inclusion and exclusion criteria were set to screen the literature.

RESULTS

A total of 163 literatures were obtained through database retrieval. After removing the duplicate literature, reading the title and abstract, and reviewing the full text finally, 34 articles were included in the final study. Most of the articles have summarized the surgical methods to correct alar retraction by retrospective study.

CONCLUSIONS

Alar retraction should be analyzed from the etiology, pathogenesis, and treatment. The diversity of surgical methods provides more options for the clinic. However, the plastic surgeons need to develop sharp analytical skills, improve clinical operational capability, and look for appropriate methods to achieve in good result.

Computational technology for nasal cartilage-related clinical research and application

Surgeons need to understand the effects of the nasal cartilage on facial morphology, the function of both soft tissues and hard tissues and nasal function when performing nasal surgery. In nasal cartilage-related surgery, the main goals for clinical research should include clarification of surgical goals, rationalization of surgical methods, precision and personalization of surgical design and preparation and improved convenience of doctor-patient communication. Computational technology has become an effective way to achieve these goals. Advances in three-dimensional (3D) imaging technology will promote nasal cartilage-related applications, including research on computational modelling technology, computational simulation technology, virtual surgery planning and 3D printing technology. These technologies are destined to revolutionize nasal surgery further. In this review, we summarize the advantages, latest findings and application progress of various computational technologies used in clinical nasal cartilage-related work and research. The application prospects of each technique are also discussed.

A FEA-Based Methodology to Predict the Osteotome Wear Status during Nasal Bone Surgical Operations

A FEA-based methodology was developed in order to predict the wear status of an osteotome (surgical instrument) during its use in a lateral nasal bone osteotomy considering its fatigue strength. The latter parameter was determined by appropriate FEM-evaluation of the perpendicular impact test results. For the simulation of the surgical procedure, two scenarios were examined: (i) when utilizing a brand new osteotome and (ii) when utilizing an already used osteotome characterized by decreased fatigue strength. The actual nasal bone geometry used in the FEA model was obtained from a high-resolution, maxillofacial, computed tomography (CT) scan of a single patient. In both cases examined, depiction of fracture patterns for the osteotome and the nasal bone were obtained. The wear of a new osteotome and an already used osteotome was also calculated and compared. The developed von Mises stresses in both the osteotome and nasal bone were depicted. The proposed methodology allowed an accurate prediction of the critical number of impacts that the osteotome can receive during the lateral nasal osteotomy which is followed in all rhinoplasties. Based on the developed methodology, a preventive replacement of the osteotome before its extensive fracture can be determined, thereby minimizing the risk of postoperative complications.

Association of Nasal Tip Rotation Outcome Estimation With the New Domes Technique in Primary Rhinoplasty

Importance

The postoperative changes in the rotation of the nasal tip in rhinoplasty must be estimated for the surgical planning.

Objective

To determine whether the outcome in the rotation angle of the nasal tip can be estimated in patients undergoing primary rhinoplasty with the new domes technique.

Design, Setting, and Participants

This retrospective analytic cohort study included 323 patients undergoing primary rhinoplasty with the new domes technique in a private clinic in Bogotá, Colombia, by a single surgeon from January 1, 2011, through January 31, 2016. Patients undergoing secondary rhinoplasty and those with less than 6 months of follow-up were excluded.

Exposures

Primary rhinoplasty using the new domes technique.

Main Outcomes and Measures

Measurement of the rotation angle of the nasal tip before and 1 week and 6 months after surgery. The main variable taken into consideration was the measurement, in millimeters, of the lateralized nasal domes.

Results

A total of 323 patients (288 women [89.2%] and 35 men [10.8%]; mean age, 27.8 years; age range, 13-70 years) were included in the study. The mean (SD) preoperative nasolabial angle was 92.7° (4.4°; range, 77°-107°); at 1 postoperative week, 105.5° (4.9°; range, 92°-120°); and at 6 postoperative months, 102.1° (4.6°; range, 90°-115°). The mean (SD) increase of the rotation that was achieved per lateralized millimeter was 3.6° (2.0°). The mean (SD) rotation angle at 6 months decreased to 3.4° (2.4°).

Conclusions and Relevance

The new domes technique was reliable and reproducible in most patients. Despite the unpredictable inflammatory changes, the exact lateralization in millimeters with the new domes technique allowed precise estimation of the long-term outcome of the rotation of the nasal tip, enabling the surgeon to determine from the preoperative plan the definitive rotation angle of the nose.

Level of Evidence

4.

Biomechanical analyses of common suspension sutures in primary cleft lip rhinoplasty

Background

For a better understanding of common suspension sutures during primary cleft lip nasal rhinoplasty, the biomechanical consequences of those sutures need to be demonstrated.

Methods

A finite element model of the infant specimen was established. The closure of cleft lip and four different specific suspension sutures were simulated by loading different forces on the model: 1. F1 to simulate the suture fastening both medial crura together; 2. F2 to simulate the suture which sewed both medial crura and the non-cleft-side upper lateral cartilage together; 3. F3 to simulate the suture elevating the alar cartilage cranially; 4. F4 to simulate the suture elevating the alar cartilage superiorly. The deformation and stress distribution consequent to each maneuver were analyzed in details.

Results

The deviation of columella was restored through the closure of cleft lip. Different suspension sutures had different biomechanical effects on the nasal structure. All suspension sutures had the function on elevating the alar cartilage. F2 had no function on restoring the collapse of the nasal tip. The suture which fastened both medial crura together leaded to the lowest stress on the skin envelope.

Conclusions

Each suspension suture had its characteristics respectively. The simulation suggested that F1, the suture which fastened both medial crura, could be the most potential maneuver for cleft lip rhinoplasty because it can symmetrically restore the shape of the nose without incurring a significant increase in stress.

Recapitulation of Unilateral Cleft Lip Nasal Deformity on Normal Nasal Structure: A Finite Element Model Analysis

Cleft lip nasal deformity has been challenging to plastic surgeons. A better understanding of the biomechanical aspect of the cleft nose would contribute to a better correction. In this study, finite element model of a normal nose was constructed and loaded with forces to recapitulate the unilateral cleft lip nasal deformity. Tether at the alar base was simulated by a laterally directed force at the lateral crus, and tether at the columella base by a posteriorly directed force at the medial crus. The equivalent von-Mises stress and the total deformation consequent to different patterns of loading were captured. In accordance with clinical observations, unilaterally loaded forces caused deformation on both sides of the nose. A correlation between the patterns of loading and different cleft lip nasal deformities was documented in detail. When set at the same force magnitude, tether at the columella base led to more extensive changes in the nasal morphology and higher level of stress than at the alar base. Clear identification of major pathological tethers in the nasolabial region might lead to more accurate and stable correction of cleft lip nasal deformities.

Grafting Techniques in Primary and Revision Rhinoplasty

With the adoption of open structure techniques, rhinoplasty has become more reliant on the use of structural grafts to resist change that occurs over time owing to both gravity and the aging process. As surgical procedures have become more technically complex, the type of grafts use for both primary and secondary rhinoplasty have undergone significant evolution. This article provides a case approach focused on the use of structural grafting in rhinoplasty.

Biomechanical simulation of correcting primary unilateral cleft lip nasal deformity

For better outcomes of the primary correction of cleft lip nasal deformity, it is important to clarify the specific morphological and biomechanical consequences of major surgical maneuvers during cleft lip nose correction. In this study, a finite element model was established basing on the micro-MRI imaging of an infant specimen with unilateral complete cleft lip deformity. Alar base adduction was simulated as a medially-directed force on the lateral crus (F1); columella straightening was simulated as a laterally-directed force on the medial crus (F2); and nasal tip enhancement was simulated as an anteriorly-directed force on the intermediate crus (F3). The deformation and stress distribution consequent to each force vector or different force combinations were analyzed in details. Our biomechnical analyses suggested that W\when loaded alone, the three forces generated disparate morphological changes. The combination of different force loadings generated obviously different outcomes. F3 generated the most intensive stress when compared to F1 and F2. When F2 was loaded on top of F1-F3 combination, it further relieved nasal deviation without incurring significant increase in stress. Our simulation suggested that alar base adduction, columella straightening, and nasal tip elevation should all be included in a competent cleft lip nose correction.

Mechanical analyses of critical surgical maneuvers in the correction of cleft lip nasal deformity

The relapse of nasal deformity is a challenge for modern correction of cleft lip. A comprehensive understanding in the biomechanical perspective of both the formation and correction of the cleft lip nasal deformity would lead to improved stability of the corrective outcome. In this study, a finite element model of secondary cleft lip nasal deformity was constructed, on which two critical corrective maneuvers were mimicked in the form of force-loading. The intercrural suture was simulated by a force loaded at the intermediate crus of the alar cartilage directing anteriorly and medially, and the suture suspending the alar cartilage to the upper lateral cartilage was simulated by a force loaded at the lateral crus directing superiorly and medially. The equivalent von-mises stress and the total deformation consequent to different patterns of loading were captured. Our biomechanical analyses suggested that the intercrural suture at the nasal tip might be more effective in generating widespread morphological change than the suspension suture, but left much higher level of stress within the skin envelope if placed too high. Synergistic effect was observed between the two sutures in both the resultant deformation and stress. In addition, our simulations were partially supported by clinical photogrammetry data.

Estimation of Nasal Tip Support Using Computer-Aided Design and 3-Dimensional Printed Models

IMPORTANCE

Palpation of the nasal tip is an essential component of the preoperative rhinoplasty examination. Measuring tip support is challenging, and the forces that correspond to ideal tip support are unknown.

OBJECTIVE

To identify the integrated reaction force and the minimum and ideal mechanical properties associated with nasal tip support.

DESIGN, SETTING, AND PARTICIPANTS

Three-dimensional (3-D) printed anatomic silicone nasal models were created using a computed tomographic scan and computer-aided design software. From this model, 3-D printing and casting methods were used to create 5 anatomically correct nasal models of varying constitutive Young moduli (0.042, 0.086, 0.098, 0.252, and 0.302 MPa) from silicone. Thirty rhinoplasty surgeons who attended a regional rhinoplasty course evaluated the reaction force (nasal tip recoil) of each model by palpation and selected the model that satisfied their requirements for minimum and ideal tip support. Data were collected from May 3 to 4, 2014.

RESULTS

Of the 30 respondents, 4 surgeons had been in practice for 1 to 5 years; 9 surgeons, 6 to 15 years; 7 surgeons, 16 to 25 years; and 10 surgeons, 26 or more years. Seventeen surgeons considered themselves in the advanced to expert skill competency levels. Logistic regression estimated the minimum threshold for the Young moduli for adequate and ideal tip support to be 0.096 and 0.154 MPa, respectively. Logistic regression estimated the thresholds for the reaction force associated with the absolute minimum and ideal requirements for good tip recoil to be 0.26 to 4.74 N and 0.37 to 7.19 N during 1- to 8-mm displacement, respectively.

CONCLUSIONS AND RELEVANCE

This study presents a method to estimate clinically relevant nasal tip reaction forces, which serve as a proxy for nasal tip support. This information will become increasingly important in computational modeling of nasal tip mechanics and ultimately will enhance surgical planning for rhinoplasty.

LEVEL OF EVIDENCE

NA.

Advances in Technology for Functional Rhinoplasty: The Next Frontier

Advances in computer modeling and simulation technologies have the potential to provide facial plastic surgeons with information and tools that can aid in patient-specific surgical planning for rhinoplasty. Finite element modeling and computational fluid dynamics are modeling technologies that have been applied to the nose to study structural biomechanics and nasal airflow. Combining these technologies with patient-specific imaging data and symptom measures has the potential to alter the future landscape of nasal surgery.

A Finite Element Model to Simulate Formation of the Inverted-V Deformity

IMPORTANCE

Computational modeling can be used to mimic the forces acting on the nasal framework that lead to the inverted-V deformity (IVD) after surgery and potentially determine long-range outcomes.

OBJECTIVE

To demonstrate the use of the finite element method (FEM) to predict the formation of the IVD after separation of the upper lateral cartilages (ULCs) from the nasal septum.

DESIGN, SETTING, AND PARTICIPANTS

A computer model of a nose was derived from human computed tomographic data. The septum and upper and lower lateral cartilages were designed to fit within the soft-tissue envelope using computer-aided design software. Mechanical properties were obtained from the literature. The 3 simulations created included (1) partial fusion of the ULCs to the septum, (2) separation of the ULCs from the septum, and (3) a fully connected model to serve as a control. Forces caused by wound healing were prescribed at the junction of the disarticulated ULCs and septum. Using FEM software, equilibrium stress and strain were calculated. Displacement of the soft tissue along the nasal dorsum was measured and evaluated for evidence of morphologic change consistent with the IVD.

MAIN OUTCOME AND MEASURES

Morphologic changes on the computer models in response to each simulation.

RESULTS

When a posteroinferior force vector was applied along the nasal dorsum, the areas of highest stress were along the medial edge of the ULCs and at the junction of the ULCs and the nasal bones. With full detachment of ULCs and the dorsal septum, the characteristic IVD was observed. Both separation FEMs produced a peak depression of 0.3 mm along the nasal dorsum.

CONCLUSIONS AND RELEVANCE

The FEM can be used to simulate the long-term structural complications of a surgical maneuver in rhinoplasty, such as the IVD. When applied to other rhinoplasty maneuvers, the use of FEMs may be useful to simulate the long-term outcomes, particularly when long-term clinical results are not available. In the future, use of FEMs may simulate rhinoplasty results beyond simply morphing the outer contours of the nose and allow estimation of potentially long-term clinical outcomes that may not be readily apparent.

LEVEL OF EVIDENCE

NA.