Deformation of nasal septum during nasal trauma

Composite Thickness and Stiffness Analysis of the Nasal Septum

Background: The nasal septum supports the structure of the nose and is frequently manipulated during septorhinoplasty. Objective: To compare measurements of thickness and compressive Young's modulus (YM) between different regions of nasal septa from human anatomic specimens. Study Design: Case series. Methods: Cartilaginous septa from human anatomic specimens were dissected. Septum thickness was measured at 24 points with regular intervals using a digital caliper. Compressive YM was determined at 14 regions using a force gauge. Two-tailed student's t-tests were used to compare the average thickness and YM between different regions. Results: Septa from 40 human anatomic specimens were included, with age ranging from 50 to 89. Fifty percent of specimens were female. The mean (standard deviation) thickness of the septum was 1.75 (0.76) mm. The mean YM was 2.38 (1.29) MPa. The septum was thickest near the maxillary crest (3.09 [1.17] mm) and the keystone area (2.52 [0.91] mm) and thinnest near the anterior septal angle (1.29 [0.58] mm). The septum was most stiff posteriorly (2.90 [1.32] MPa) and least stiff anteriorly (1.80 [1.15] MPa). Conclusion: The nasal septum is thickest posteriorly, inferiorly, and along its bony edges. The septum is stiffest posteriorly, ventrally, and along its bony edges.

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.

Beyond the L-Strut: Redefining the Biomechanics of Rhinoplasty Using Topographic Optimization Modeling

Rhinoplasty utilizes cartilage harvested from the nasal septum as autologous graft material. Traditional dogma espouses preservation of the "L-strut" of dorsal and caudal septum, which is less resistant to axial loading than virgin septum. Considering the 90° angle between dorsal and caudal limbs, the traditional L-strut also suffers from localized increases in internal stresses leading to premature septal "cracking," structural-scale deformation, or both. Deformation and failure of the L-strut leads to nasal deviation, saddle deformity, loss of tip support, or restriction of the nasal valve. The balance between cartilage yield and structural integrity is a topographical optimization problem. Guided by finite element (FE) modelling, recent efforts have yielded important modifications including the chamfering of right-angled corners to reduce stress concentrations and the preservation of a minimum width along the inferior portion of the caudal strut. However, all existing FE studies offer simplified assumptions to make the construct easier to model. This review article highlights advances in our understanding of septal engineering and identifies areas that require more work to further refine the balance between the competing interests of graft acquisition and the maintenance of nasal structural integrity.

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.

Septal fractures predict poor outcomes after closed nasal reduction: Retrospective review and survey

OBJECTIVES/HYPOTHESIS

To determine outcomes of patients with displaced nasal bone fractures after closed nasal reduction (CNR).

STUDY DESIGN

Retrospective patient review.

METHODS

Review of all patients presenting to the emergency department of a tertiary-care, level 1 trauma hospital with a nasal bone fracture over a 2-year period, followed by telephone survey after CNR.

RESULTS

Six hundred seven patients presented to the emergency department in 2015 and 2016 with a diagnosis of nasal bone fracture. Of these, 134 patients met inclusion criteria and underwent CNR without septal reduction. Those with sports-related injuries and those with a septal fracture identified on computed tomography imaging were significantly more likely to undergo CNR. Ninety-one patients completed the post-CNR telephone survey. Over 90% of patients were satisfied with the procedure. However, patients with septal fractures reported worse outcomes, as 53.6% versus 24.1% (P = .0025) disagreed that CNR improved nasal breathing. Of all patients, 11 (2%) eventually underwent septorhinoplasty, with the presence of septal fracture on imaging a significant risk factor.

CONCLUSIONS

Nasal bone fractures are a common injury, often managed initially with CNR. Patients with septal fractures should be counseled on the high risk of posttraumatic nasal deformity and obstruction despite CNR. In addition, addressing a septal fracture found on imaging may be warranted with either closed septal reduction or early aggressive management given the poorer outcomes seen in the present study. Although these patients are more likely to have definitive treatment, many forego later intervention despite persistent symptoms, emphasizing the need for early intervention or close follow-up.

LEVEL OF EVIDENCE

3 Laryngoscope, 129:1784-1790, 2019.

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.

The biomechanical role of the chondrocranium and sutures in a lizard cranium

The role of soft tissues in skull biomechanics remains poorly understood. Not least, the chondrocranium, the portion of the braincase which persists as cartilage with varying degrees of mineralization. It also remains commonplace to overlook the biomechanical role of sutures despite evidence that they alter strain distribution. Here, we examine the role of both the sutures and the chondrocranium in the South American tegu lizard Salvator merianae We use multi-body dynamics analysis (MDA) to provide realistic loading conditions for anterior and posterior unilateral biting and a detailed finite element model to examine strain magnitude and distribution. We find that strains within the chondrocranium are greatest during anterior biting and are primarily tensile; also that strain within the cranium is not greatly reduced by the presence of the chondrocranium unless it is given the same material properties as bone. This result contradicts previous suggestions that the anterior portion (the nasal septum) acts as a supporting structure. Inclusion of sutures to the cranium model not only increases overall strain magnitudes but also leads to a more complex distribution of tension and compression rather than that of a beam under sagittal bending.

Yield Strength Testing in Human Cadaver Nasal Septal Cartilage and L-Strut Constructs

Importance

To our knowledge, yield strength testing in human nasal septal cartilage has not been reported to date. An understanding of the basic mechanics of the nasal septum may help surgeons decide how much of an L-strut to preserve and how much grafting is needed.

Objectives

To determine the factors correlated with yield strength of the cartilaginous nasal septum and to explore the association between L-strut width and thickness in determining yield strength.

Design, Setting, and Participants

In an anatomy laboratory, yield strength of rectangular pieces of fresh cadaver nasal septal cartilage was measured, and regression was performed to identify the factors correlated with yield strength. To measure yield strength in L-shaped models, 4 bonded paper L-struts models were constructed for every possible combination of the width and thickness, for a total of 240 models. Mathematical modeling using the resultant data with trend lines and surface fitting was performed to quantify the associations among L-strut width, thickness, and yield strength. The study dates were November 1, 2015, to April 1, 2016.

Main Outcomes and Measures

The factors correlated with nasal cartilage yield strength and the associations among L-strut width, thickness, and yield strength in L-shaped models.

Results

Among 95 cartilage pieces from 12 human cadavers (mean [SD] age, 67.7 [12.6] years) and 240 constructed L-strut models, L-strut thickness was the only factor correlated with nasal septal cartilage yield strength (coefficient for thickness, 5.54; 95% CI, 4.08-7.00; P < .001), with an adjusted R2 correlation coefficient of 0.37. The mean (SD) yield strength R2 varied with L-strut thickness exponentially (0.93 [0.06]) for set widths, and it varied with L-strut width linearly (0.82 [0.11]) or logarithmically (0.85 [0.17]) for set thicknesses. A 3-dimensional surface model of yield strength with L-strut width and thickness as variables was created using a 2-dimensional gaussian function (adjusted R2 = 0.94). Estimated yield strengths were generated from the model to allow determination of the desired yield strength with different permutations of L-strut width and thickness.

Conclusions and Relevance

In this study of human cadaver nasal septal cartilage, L-strut thickness was significantly associated with yield strength. In a bonded paper L-strut model, L-strut thickness had a more important role in determining yield strength than L-strut width. Surgeons should consider the thickness of potential L-struts when determining the amount of cartilaginous septum to harvest and graft.

Level of Evidence

NA.

A Model to Estimate L-Strut Strength With an Emphasis on Thickness

IMPORTANCE

To perform and teach septorhinoplasty, one must have a principled understanding of the mechanics of the nasal septum. The thickness of the L-strut and how it changes septal strength have not been adequately quantified, yet calculating septal strength based on changes to thickness and size is vital in maintaining lasting nasal strength and integrity.

OBJECTIVE

To establish standards for the nasal septal cartilage thickness, dorsal and caudal septum length, and Young's modulus. To provide a basis for quantitative, operative decision making, a mathematical model of L-strut strength is presented based on changes in thickness and width.

DESIGN, SETTING, AND PARTICIPANTS

Nasal septal cartilages from 30 fresh cadavers were used to measure thickness at clinically relevant points and length of dorsal and caudal L-strut arms. The Young modulus was directly measured using a force gauge. Statistical analyses were performed to compare thicknesses in anatomically relevant areas. Using a cantilevered beam construct, the spring constant of the L-strut dorsal and caudal arms were estimated individually with width and thickness as variables.

MAIN OUTCOMES AND MEASURES

Thickness, dorsal and caudal length, and the Young modulus of nasal septal cartilage. Spring constants of dorsal and caudal L-strut arms with different combinations of thickness and width.

RESULTS

The mean (SD) age at death of the 30 cadavers was 79.2 (13.6) years (range 50-97 years). Of these, 17 (57%) were male, and 13 (43%) were female. The mean (SD) nasal septal cartilage thickness in the 30 cadavers was 1.45 (0.54) mm. Mean (SD) thickness of points along the 2-mm L-strut line was 1.49 (0.56) mm and was significantly thicker than points along the 5-mm L-strut line (mean [SD] thickness, 1.29 [0.52] mm) but significantly thinner than points along the 15-mm L-strut line (mean [SD] thickness, 1.68 [0.53]). Mean (SD) thicknesses of the posterior dorsal and caudal cartilage points were 1.52 (0.45) mm and 1.71 (0.69) mm and were significantly thicker than the anterior dorsal and caudal points (mean [SD] thickness, 1.28 [0.42] mm and 1.31 [0.44] mm, respectively). Mean (SD) dorsal and caudal L-strut arm lengths were 21.9 (3.7) mm and 20.9 (3.5) mm, respectively. The mean (SD) Young modulus was 2.03 (1.3) MPa. A model was generated demonstrating the thickness required to maintain a desired strength at a given dorsal or caudal arm width.

CONCLUSIONS AND RELEVANCE

Although thickness was not uniform throughout the nasal septum, there is a predictable pattern. Thickness of the L-strut contributes more to septal strength than does L-strut width. The model generated in this study can be used in planning, performing, or teaching the applied mechanics of septorhinoplasty.

LEVEL OF EVIDENCE

NA.

Quantifying Optimal Columellar Strut Dimensions for Nasal Tip Stabilization After Rhinoplasty via Finite Element Analysis

IMPORTANCE

The contribution of columellar strut grafts (CSGs) to nasal tip support has not been determined via structural mechanics. Optimal graft dimensions have yet to be objectively determined.

OBJECTIVES

To use a finite element model (FEM) of the human nose to (1) determine the effect of the CSG on nasal tip support and (2) identify how suture placement contributes to tip support.

DESIGN, SETTING, AND PARTICIPANTS

A multiple-component FEM of the human nose consisting of bone, skin/soft tissue, and cartilage was rendered from a computed tomographic scan. Then, CSGs of varying sizes were created, ranging from 15 × 4 × 1 mm to 25 × 8 × 1 mm, and placed in the model between the medial crura. Two FEMs were constructed for each strut size: (1) CSGs that were physically attached to the nasal spine, medial crura, and caudal septum and (2) CSGs that were not in direct contact with these structures and free to move within the soft tissue. A control model was also constructed wherein no graft was placed.

MAIN OUTCOMES AND MEASURES

Nasal tip support for each model was assessed, and the resultant distribution of von Mises stress, reaction force, and strain energy density with respect to the alar cartilages were calculated.

RESULTS

Compared with the control, the reaction force increased with increasing strut volume, while the strain energy density (calculated over the alar cartilages) generally decreased with increasing CSG volume. Simulations with struts that had suture attachments along the entire length of the graft generated a larger reaction force than the models without any suture attachments. Models with anteriorly placed sutures generated reaction forces similar to that of the fully sutured model, whereas the models with posterior sutures showed reaction forces similar to the fully disconnected model.

CONCLUSIONS AND RELEVANCE

Insertion of CSGs does effect the amount of force the nasal tip can withstand post rhinoplasty. Moreover, anteriorly placed sutures incur reaction forces similar to struts that are fully connected to the alar cartilage. Thus, our simulations are congruent with clinical practice in that stability increases with graft size and fixation, and that sutures should be placed along either the entire CSG or the anterior most portion for optimal support.

LEVEL OF EVIDENCE

NA.

Redefining the Septal L-Strut to Prevent Collapse

During septorhinoplasty, septal cartilage is frequently resected for various purposes but the L-strut is preserved. Numerous materials are inserted into the nasal dorsum during dorsal augmenation rhinoplasty without considering nasal structural safety. This study used a finite element method (FEM) to redefine the septal L-strut, to prevent collapse as pressure moved from the rhinion to the supratip breakpoint on the nasal dorsum and as the contact percentage between the caudal L-strut and the maxillary crest changed. We designed a 1-cm-wide L-strut model based on computed tomography data. At least 45% of the width of the L-strut in the inferior portion of the caudal strut must be preserved during septoplasty to stabilize the septum. In augmentation rhinoplasty, the caudal L-strut must either be preserved perfectly or reinforced to prevent collapse or distortion of the L-strut. The dorsal augmentation material must be fixed in an augmentation pocket to prevent movement of graft material toward the supratip breakpoint, which can disrupt the L-strut. We conducted a numerical analysis using a FEM to predict tissue/organ behavior and to help clinicians understand the reasons for target tissue/organ collapse and deformation.

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.

Finite Element Model Analysis of Cephalic Trim on Nasal Tip Stability

IMPORTANCE

Alar rim retraction is the most common unintended consequence of tissue remodeling that results from overresection of the cephalic lateral crural cartilage; however, the complex tissue remodeling process that produces this shape change is not well understood.

OBJECTIVES

To simulate how resection of cephalic trim alters the stress distribution within the human nose in response to tip depression (palpation) and to simulate the internal forces generated after cephalic trim that may lead to alar rim retraction cephalically and upward rotation of the nasal tip.

DESIGN, SETTING, AND PARTICIPANTS

A multicomponent finite element model was derived from maxillofacial computed tomography with 1-mm axial resolution. The 3-dimensional editing function in the medical imaging software was used to trim the cephalic portion of the lower lateral cartilage to emulate that performed in typical rhinoplasty. Three models were created: a control, a conservative trim, and an aggressive trim. Each simulated model was imported to a software program that performs mechanical simulations, and material properties were assigned. First, nasal tip depression (palpation) was simulated, and the resulting stress distribution was calculated for each model. Second, long-term tissue migration was simulated on conservative and aggressive trim models by placing normal and shear force vectors along the caudal and cephalic borders of the tissue defect.

RESULTS

The von Mises stress distribution created by a 5-mm tip depression revealed consistent findings among all 3 simulations, with regions of high stress being concentrated to the medial portion of the intermediate crus and the caudal septum. Nasal tip reaction force marginally decreased as more lower lateral cartilage tissue was resected. Conservative and aggressive cephalic trim models produced some degree of alar rim retraction and tip rotation, which increased with the magnitude of the force applied to the region of the tissue defect.

CONCLUSIONS AND RELEVANCE

Cephalic trim was performed on a computerized composite model of the human nose to simulate conservative and aggressive trims. Internal forces were applied to each model to emulate the tissue migration that results from decades of wound healing. Our simulations reveal that the degree of tip rotation and alar rim retraction is dependent on the amount of cartilage that was resected owing to cephalic trim. Tip reaction force is marginally reduced with increasing tissue volume resection.

LEVEL OF EVIDENCE

NA.

Investigation of the relationship between facial injuries and traumatic brain injuries using a realistic subject-specific finite element head model

In spite of anatomic proximity of the facial skeleton and cranium, there is lack of information in the literature regarding the relationship between facial and brain injuries. This study aims to correlate brain injuries with facial injuries using finite element method (FEM). Nine common impact scenarios of facial injuries are simulated with their individual stress wave propagation paths in the facial skeleton and the intracranial brain. Fractures of cranio-facial bones and intracranial injuries are evaluated based on the tolerance limits of the biomechanical parameters. General trend of maximum intracranial biomechanical parameters found in nasal bone and zygomaticomaxillary impacts indicates that severity of brain injury is highly associated with the proximity of location of impact to the brain. It is hypothesized that the midface is capable of absorbing considerable energy and protecting the brain from impact. The nasal cartilages dissipate the impact energy in the form of large scale deformation and fracture, with the vomer-ethmoid diverging stress to the "crumpling zone" of air-filled sphenoid and ethmoidal sinuses; in its most natural manner, the face protects the brain. This numerical study hopes to provide surgeons some insight in what possible brain injuries to be expected in various scenarios of facial trauma and to help in better diagnosis of unsuspected brain injury, thereby resulting in decreasing the morbidity and mortality associated with facial trauma.

Redefining the septal L-strut in septal surgery

In septal surgery, the surgeon preserves the L-strut, the portion anterior to a vertical line drawn from the rhinion to the anterior nasal spine (ANS) and at least a 1-cm width of the dorsal and caudal septal segment, to decrease the potential for loss of the tip and dorsal nasal support. However, nasal tip collapse and saddle deformities occur occasionally. We utilized a mechanical approach to determine the safe width size for the L-strut in contact with the maxillary crest. Five L-strut models were designed based on computed tomography data (80 patients) and previous studies (55 patients). All L-strut models connected the perpendicular plate of the ethmoid bone (PPE) and the maxillary crest and were assumed to be fixed to the PPE and maxillary crest. An approximated daily load was applied to the dorsal portion of the L-strut. Finite element analyses were performed to compare the stress, strain, and displacement distribution of all L-strut models. According to the differences in the contact area between the caudal L-strut and maxillary crest, there are significant differences in terms of the stress, strain, and displacement distribution in the L-strut. High stresses occurred at the inner corner of the L-strut when 60 - 100% of the strut was in contact with the maxillary crest. High stresses also occurred at the inferior portion of the caudal L-strut when 20 - 40% of the caudal strut was in contact with maxillary crest. We conclude that it is important to preserve the 1-cm width L-strut caudal segment, which corresponds to the portion posterior to a vertical line drawn from the rhinion to the ANS. In particular, we must maintain more than 40% of the contact area between the L-strut and the maxillary crest when the septal cartilage in the caudal portion of the L-strut is harvested.

Rethinking nasal tip support: a finite element analysis

OBJECTIVE

We employ a nasal tip finite element model (FEM) to evaluate contributions of two of the three major tip support mechanisms: attachments between the upper and lower lateral cartilages and attachment of the medial crura to the caudal septum.

STUDY DESIGN

The nasal tip FEM computed stress distribution and strain energy density (SED) during nasal tip compression. We examined the impact of attachments between the upper and lower lateral cartilages and the attachment of the medial crura to the caudal septum on nasal tip support.

METHODS

The FEM consisted of three tissue components: bone, cartilage, and skin. Four models were created: A) control model with attachments present at the scroll and caudal septum; B) simulated disruption of scroll; C) simulated disruption of medial crura attachments to caudal septum; and D) simulated disruption of scroll and medial crura attachments to caudal septum. Spatial distribution of stress and SED were calculated.

RESULTS

The keystone, intermediate crura, caudal septum, and nasal spine demonstrated high concentration of stress distribution. Across all models, there was no difference in stress distribution. Disruption of the scroll resulted in 1% decrease in SED. Disruption of the medial crura attachments to the caudal septum resulted in 4.2% reduction in SED. Disruption of both scroll and medial crural attachments resulted in 9.1% reduction in SED.

CONCLUSION

The nasal tip FEM is an evolving tool to study structural nasal tip dynamics and demonstrates the loss of nasal tip support with disruption of attachments at the scroll and nasal base.

LEVEL OF EVIDENCE

N/A.

Compressive and tensile mechanical properties of the porcine nasal septum

The expanding nasal septal cartilage is believed to create a force that powers midfacial growth. In addition, the nasal septum is postulated to act as a mechanical strut that prevents the structural collapse of the face under masticatory loads. Both roles imply that the septum is subject to complex biomechanical loads during growth and mastication. The purpose of this study was to measure the mechanical properties of the nasal septum to determine (1) whether the cartilage is mechanically capable of playing an active role in midfacial growth and in maintaining facial structural integrity and (2) if regional variation in mechanical properties is present that could support any of the postulated loading regimens. Porcine septal samples were loaded along the horizontal or vertical axes in compression and tension, using different loading rates that approximate the in vivo situation. Samples were loaded in random order to predefined strain points (2-10%) and strain was held for 30 or 120 seconds while relaxation stress was measured. Subsequently, samples were loaded until failure. Stiffness, relaxation stress and ultimate stress and strain were recorded. Results showed that the septum was stiffer, stronger and displayed a greater drop in relaxation stress in compression compared to tension. Under compression, the septum displayed non-linear behavior with greater stiffness and stress relaxation under faster loading rates and higher strain levels. Under tension, stiffness was not affected by strain level. Although regional variation was present, it did not strongly support any of the suggested loading patterns. Overall, results suggest that the septum might be mechanically capable of playing an active role in midfacial growth as evidenced by increased compressive residual stress with decreased loading rates. However, the low stiffness of the septum compared to surrounding bone does not support a strut role. The relatively low stiffness combined with high stress relaxation under fast loading rates suggests that the nasal septum is a stress dampener, helping to absorb and dissipate loads generated during mastication.

Nasal tip support: a finite element analysis of the role of the caudal septum during tip depression

OBJECTIVES/HYPOTHESIS

Although minor and major tip support mechanisms have been described in detail, no quantitative models exist to provide support for the relative contributions of the structural properties of the major alar cartilage, the fibrous attachments to surrounding structures, and the rigid support structures in an objective manner.

STUDY DESIGN

The finite element method was used to compute the stress distribution in the nose during simple tip compression, and then identify the specific anatomic structures that resist deformation and thus contribute to tip support. Additionally, the impact of caudal septal resection on nasal tip support was examined.

METHODS

The computer models consisted of three tissue components with anatomically correct geometries for skin and bone derived from computed tomographic data. Septum, upper lateral cartilages, and major alar cartilages were fitted within the model using three-dimensional computer-aided design software. Five-millimeter nasal tip compression was performed on the models with caudal septal resection (3 and 5 mm) and without resection to simulate palpation, then the resulting spatial distribution of stress and displacement was calculated.

RESULTS

The von Mises stress in the normal model was primarily concentrated along the medial crural angle. As caudal septum length was reduced, stress was redistributed to adjacent soft tissue and bone, resulting in less force acting on the septum. In all models, displacement was greatest near the intermediate crura.

CONCLUSIONS

These models are the first step in the comprehensive mechanical analysis of nasal tip dynamics. Our model supports the concept of the caudal septum and major alar cartilage providing the majority of critical load-bearing support.

Preliminary Deformational Studies on a Finite Element Model of the Nasal Septum Reveals Key Areas for Septal Realignment and Reconstruction

Background. With the current lack of clinically relevant classification methods of septal deviation, computer-generated models are important, as septal cartilage is indistinguishable on current imaging methods, making preoperative planning difficult. Methods. Three-dimensional models of the septum were created from a CT scan, and incremental forces were applied. Results. Regardless of the force direction, with increasing force, the septum first tilts (type I) and then crumples into a C shape (type II) and finally into an S shape (type III). In type I, it is important to address the dislocation in the vomer-ethmoid cartilage junction and vomerine groove, where stress is concentrated. In types II and III, there is intrinsic fracture and shortening of the nasal septum, which may be dislocated off the anterior nasal spine. Surgery aims to relieve the posterior buckling and dislocation, with realignment of the septum to the ANS and possible spreader grafts to buttress the fracture sites. Conclusion. By identifying clinically observable septal deviations and the areas of stress concentration and dislocation, a straighter, more stable septum may be achieved.

Mechanical analysis of the effects of cephalic trim on lower lateral cartilage stability

OBJECTIVE

To determine how mechanical stability changes in the lower lateral cartilage (LLC) after varying degrees of cephalic resection in a porcine cartilage nasal tip model.

METHODS

Alar cartilage was harvested from fresh porcine crania (n = 14) and sectioned to precisely emulate a human LLC in size and dimension. Flexural mechanical analysis was performed both before and after cephalic trims of 0 (control), 4, and 6 mm. Cantilever deformation tests were performed on the LLC models at 3 locations (4, 6, and 8 mm from the midline), and the integrated reaction force was measured. An equivalent elastic modulus of the crura was calculated assuming that the geometry of the LLC model approximated a modified single cantilever beam. A 3-dimensional finite element model was used to model the stress distribution of the prescribed loading conditions for each of the 3 types of LLC widths.

RESULTS

A statistically significant decrease (P = .02) in the equivalent elastic modulus of the LLC model was noted at the most lateral point at 8 mm and only when 4 mm of the strut remained (P = .05). The finite element model revealed that the greatest internal stresses was at the tip of the nose when tissue was flexed 8 mm from the midline.

CONCLUSION

Our results provide the mechanical basis for suggested clinical guidelines stating that a residual strut of less than 6 mm can lead to suboptimal cosmetic results owing to poor structural support of the overlying skin soft-tissue envelope by an overly resected LLC.

Postoperative effects of anterior nasal spine bone harvesting on overall nasal shape

AIM

Bone harvesting from the anterior nasal spine (ANS) is frequently used to correct peri-implant bone defects, particularly during implant placement in the anterior maxilla. However, many clinicians are concerned about the postoperative effect of removing the ANS on the nasal outline, as the ANS is integral to supporting the nose. This study aimed to describe the technique of ANS bone grafting and to investigate postoperative effects of bone harvesting from the ANS on the overall nasal shape.

MATERIAL AND METHODS

Fifteen patients with single maxillary first incisal rehabilitation using dental implant were enrolled in this prospective clinical study. Simply by extending the subperiosteal dissection in the same surgical field without additional local anesthesia, a bone block of about 0.25-0.5 ml could be harvested from the ANS. Nose width (NW), nasolabial angle (NLA), and nasal tip depth (NTD) were measured and analyzed by lateral and frontal photographs taken preoperatively (T0), and at postoperative 1 week (T1), 3 months (T2), and 6 months (T3). Postoperative complications were also recorded.

RESULTS

A significant increase in NW and decrease in both NLA and NTD were found at T1 (P < 0.05). At T3, NW, NLA and NTD returned to preoperative measurements at T0 without major complications.

CONCLUSIONS

The ANS could be an effective and easily accessible intraoral source for autologous bone. Despite acute soft tissue swelling, the net postoperative effects of removing the ANS on the overall nasal shape, including on nasal tip collapse or widening of the nose base, were negligible.