Development and validation of an optimized finite element model of the human orbit

Biomechanical Analysis of Orbital Development: A Finite Element Analysis by an Experimentally Validated Model

AIMS

Constructing orbital finite element models capable of simulating the development process and analyzing the biomechanical mechanism.

METHODS

Four normal orbits from 1-month-old New Zealand white rabbits were used in this study. Toshiba Aquilion Prime was used to determine the computed tomography scan and direct orbital pressure manometry using an improved manometer based on the TSD104 pressure sensor transducer. The finite element analysis was conducted using the ANSYS Workbench platform.

RESULTS

The biomechanics of each orbital wall improved to varying degrees as the rabbit orbit grew and developed. The von Mises stress in both rabbits initially concentrated at the lower edge of the posterior orbital wall, expanded to the entire orbit, and ultimately became more significant in the biomechanics of the region that consisted of the posterior orbital and superior orbital walls. During the expansion phase, the biomechanics of both rabbits gradually developed from the nasal side to the occipital side for radial displacement. It is evident that the finite element model is a good fit for simulating the physiological development of the rabbit orbit. The maximum radial displacement and maximum von Mises stress appeared 2 intermissions during the development of the orbit, at about 50 to 60 days and 80 to 90 days.

CONCLUSION

This study establishes a theoretical foundation for the creation of a biomechanical model of human orbital development by offering the first finite element model to simulate orbital development and analyze the biomechanical mechanism of orbital pressure on orbital development.

Biomechanical analysis of fixation methods for bone flap repositioning after lateral orbitotomy approach: A finite element analysis

OBJECTIVE

In ophthalmic surgery, different materials and fixation methods are employed for bone flap repositioning after lateral orbitotomy approach (LOA), yet there is no unified standard. This study aims to investigate the impact of different fixation strategies on orbital stability through Finite Element Analysis (FEA) simulations of the biomechanical environment for orbital rim fixation in LOA.

METHODS

A Finite Element Model (FEM) was established and validated to simulate the mechanical responses under various loads in conventional lateral orbitotomy approach (CLOA) and deep lateral orbital decompression (DLOD) using single titanium plate, double titanium plates, and double absorbable plates fixation methods. The simulations were then validated against clinical cases.

RESULTS

Under similar conditions, the maximum equivalent stress (MES) on titanium alloy fixations was greater than that on absorbable plate materials. Both under static and physiological conditions, all FEM groups ensured structural stability of the system, with material stresses remaining within safe ranges. Compared to CLOA, DLOD, which involves the removal of the lateral orbital wall, altered stress conduction, resulting in an increase of MES and maximum total deformation (MTD) by 1.96 and 2.62 times, respectively. Under a horizontal load of 50 N, the MES in FEM/DLOD exceeded the material's own strength, with an increase in MES and MTD by 3.18 and 6.64 times, respectively, compared to FEM/CLOA. Under a vertical force of 50 N, the MES sustained by each FEM was within safe limits. Bone flap rotation angles remained minimally varied across scenarios. During follow-up, the 12 patients validated in this study did not experience complications related to the internal fixation devices.

CONCLUSION

Under static or physiological conditions, various fixation methods can effectively maintain stability at the orbitotomy site, and absorbable materials, with their smoother stress transmission properties, are more suited for application in CLOA. Among titanium plate fixations, single titanium plates can better withstand vertical stress, while double titanium plates are more capable of handling horizontal stress. Given the change in the orbital mechanical behavior due to DLOD, enhanced fixation strength should be considered for bone flap repositioning.

Biomechanical analysis using finite element analysis of orbital floor fractures reproduced in a realistic experimental environment with an anatomical model

Introduction: In this study, we attempted to demonstrate the actual process of orbital floor fracture visually and computationally in anatomically reconstructed structures and to investigate them using finite element analysis. Methods: A finite element model of the skull and cervical vertebrae was reconstructed from computed tomography data, and an eyeball surrounded by extraocular adipose was modeled in the orbital cavity. Three-dimensional volume mesh was generated using 173,894 of the 4-node hexahedral solid elements. Results: For the cases where the impactor hit the infraorbital foramen, buckling occurred at the orbital bone as a result of the compressive force, and the von Mises stress exceeded 150 MPa. The range of stress components included inferior orbital rim and orbital floor. For the cases where the impactor hit the eyeball first, the orbital bone experienced less stress and the range of stress components limited in orbital floor. The critical speeds for blowout fracture were 4 m/s and 6 m/s for buckling and hydraulic mechanism. Conclusion: Each mechanism has its own fracture inducing energy and its transmission process, type of force causing the fracture, and fracture pattern. It is possible to determine the mechanism of the fracture based on whether an orbital rim fracture is present.

Mechanisms of Development of Orbital Fractures: A Review

PURPOSE

The purpose of this study is to review the mechanisms in the development of orbital fractures.

METHODS

This is a comprehensive literature review that summarizes the mechanisms of developing orbital fractures.

RESULTS

There are 3 proposed mechanisms in the development of orbital fractures, which include the buckling, hydraulic, and globe-to-wall contact mechanisms. These mechanisms, as well as patient age, causes of injuries, and periorbital anatomy, influence the extent, sites, and patterns of orbital fractures.

CONCLUSION

A deeper understanding of these mechanisms helps us to detect and properly manage orbital fractures in the clinical setting.

Do mandibular titanium miniplates affect the biomechanical behaviour of the mandible? A preliminary experimental study

INTRODUCTION

Whether to conserve or remove titanium miniplates after rigid internal fixation of mandibular fractures still remains controversial. Miniplates could affect the biomechanical behaviour of the mandible in case of trauma, and therefore cause more complex fractures.

MATERIALS AND METHODS

An experimental study, consisting in simulating a mandibular trauma, was designed in order to compare the fractures caused by an impact on the mandible in the presence or absence of an internal fixation. We simulated an impact on the right parasymphysis region in 10 post-mortem human subjects, according to the Charpy impact test method at an impact speed of 7.4 m/s, using a 5 kg test impactor.

RESULTS

In the control group, the fracture lines were vertical and straight, without comminution. In the miniplate group, the fractures occurred close to the miniplates (4 cases) and under the miniplates (one case). The fracture lines were more complex, even comminuted in 2 cases. Thus, miniplates impacted the biomechanical behavior of the mandible, resulting in more complex fractures.

CONCLUSION

Our experimental study highlighted the impact of the presence of miniplates on the mandible in case of trauma, and the risk of causing more complex fractures. We therefore recommend further investigations to determine if titanium miniplates should be systematically removed after bone healing, in patients with a higher risk of trauma in relation with previous assault injuries, alcohol or substance abuse, the practice of fighting or contact sport/activities, and soldiers.

Tensile modulus of human orbital wall bones cut in sagittal and coronal planes

In the current research, 68 specimens of orbital superior and/or medial walls taken from 33 human cadavers (12 females, 21 males) were subjected to uniaxial tension untill fracture. The samples were cut in the coronal (38 specimens) and sagittal (30 specimens) planes of the orbital wall. Apparent density (ρ_app), tensile Young’s modulus (E-modulus) and ultimate tensile strength (UTS) were identified. Innovative test protocols were used to minimize artifacts and analyze the obtained data: (1) grips dedicated to non-symmetrical samples clamping were applied for mechanical testing, (2) non-contact measuring system of video-extensometer was employed for displacement registration, (3) ink imprint technique coupled with CAD analysis was applied to precisely access the cross-sectional areas of tested samples. With regard to a pooled group, apparent density for the coronal and sagittal cut plane was equal 1.53 g/cm³ and 1.57 g/cm³, tensile Young’s modulus 2.36 GPa and 2.14 GPa, and ultimate tensile strength 12.66 MPa and 14.35 MPa, respectively. No significant statistical differences (p > 0.05) were found for all the analyzed parameters when comparing coronal and sagittal plane cut groups. These observations confirmed the hypothesis that direction of sample cut does not affect the mechanical response of the orbital wall tissue, thus suggesting that mechanical properties of orbital wall bone show isotropic character.

Validation of Hydraulic Mechanism during Blowout Trauma of Human Orbit Depending on the Method of Load Application

The more we know about mechanisms of the human orbital blowout type of trauma, the better we will be able to prevent them in the future. As long as the buckling mechanism's veracity is not in doubt, the hydraulic mechanism is not based on equally strong premises. To investigate the correctness of the hydraulic mechanism's theory, two different methods of implementation of the hydraulic load to the finite element method (FEM) model of the orbit were performed. The intraorbital hydraulic pressure was introduced as a face load applied directly to the orbit in the first variant, while in the second one the load was applied to the orbit indirectly as a set of nodal forces transferred from the external surface of the eyeball via the intraorbital tissues to the orbital walls within the contact problem. Such an approach is aimed at a better understanding of the pattern for the formation of blowout fractures during the indirect load applied to the orbital bones. The nonlinear dynamic analysis of both numerical models showed that the potential fracture was observed in the second variant only, embracing a relatively large area: both medial and lower wall of the orbit. Interestingly, the pressure generated by the intraorbital entities transferred the energy of the impact to the orbital sidewalls mainly; thus, the nature of the mechanism known as the hydraulic was far from the expected hydraulic pressure. According to the eyeball's deformation as well as the areas of the greatest Huber-Mises-Hencky (H-M-H) stress within the orbit, a new term of strut mechanism was proposed instead of the hydraulic mechanism as more realistic regarding the investigated phenomenon. The results of the current research may strongly influence the development of modern implantology as well as affect forensic medicine.

Biomechanical assessment of orbital fractures using patient-specific models and clinical matching

INTRODUCTION

Orbital wall fractures consider one of the most common fractures in the maxillofacial trauma. These fractures caused by two mechanisms, the buckling mechanism and hydraulic mechanism. This study aims to compare between the two mechanisms in terms of intensity and extension using the finite elements method.

MATERIAL AND METHODS

Three-dimensional model of the skull was generated using computed tomography data of young male patient. Virtual loads were applied on the eyeball and the infra-orbital rim separately. Von Mises stresses were examined in each simulation.

RESULTS

The simulation predicted fractures on the infra-orbital rim and orbital floor when simulating the hydraulic mechanism, and on the orbital floor and mesial wall when simulating the buckling mechanism.

CONCLUSION

Biomechanical studies are essential part in understanding maxillofacial fractures mechanisms. The results confirmed and ascertained what is seen clinically, and explained clearly the two mechanisms of orbital fractures.

Nonlinear dynamic analysis of the pure "buckling" mechanism during blow-out trauma of the human orbit

Considering the interplay between orbital bones and intraorbital soft tissues, commonly accepted patterns of the blow-out type of trauma within the human orbit require more thorough investigation to assess the minimal health-threatening impact value. Two different three-dimensional finite element method (FEM) models of the human orbital region were developed to simulate the pure “buckling” mechanism of orbital wall fracture in two variants: the model of orbital bone elements and the model of orbital bone, orbit and intraorbital tissue elements. The mechanical properties of the so-defined numerical skull fragment were applied to the model according to the unique laboratory tensile stress tests performed on small and fragile specimens of orbital bones as well as using the data available in the literature. The nonlinear transient analysis of the contact problem between bodies that differ substantially in terms of the Young’s modulus was carried out to investigate the interaction of different bodies within an instant injury. Potential damage areas were found within the lower orbital wall as well as the destructive load values for both FEM skull models (7,660 N and 8,520 N). Moreover, numerical simulations were validated by comparing them with computed tomography scans of real injuries.

Evaluation of Concomitant Orbital Floor Fractures in Patients with Head Trauma Using Conventional Head CT Scan: A Retrospective Study at a Level II Trauma Center

BACKGROUND

Patients with head trauma may have concomitant orbital floor fractures (OFFs). The objective of our study was to determine the specific CT findings and investigate the diagnostic performance of head CT in detecting OFFs.

METHODS

We analyzed 3534 head trauma patients undergoing simultaneous head and facial CT over a 3-year period. The clinical data and specific head CT findings between patients with and without OFFs were compared.

RESULTS

In our cohort, 198 patients (5.6%) had OFFs visible on CT. On head CT, orbital floor discontinuity, gas bubbles entrapped between floor fragments, inferior extraconal emphysema, and maxillary hemosinus (MHS) were more commonly observed among patients with OFFs (p < 0.001). The absence of MHS had a high negative predictive value (99.7%) for excluding OFFs. Among the different types of MHS, the pattern showing high-attenuation opacity mixed with mottled gas had the highest positive predictive value (69.5%) for OFFs and was the only independent predictor of OFFs after adjusting for the other CT variables in all patients with MHS.

CONCLUSION

Head CT may serve as a first-line screening tool to detect OFFs in head trauma patients. Hence, unnecessary facial CT and additional radiation exposure may be reduced.