Finite Element Model Of Cervical Spine Research Articles

Finite element analysis of a three-dimensional cervical spine model with muscles based on CT scan data

Background The incidence of cervical spondylosis is increasing, gradually affecting people’s normal lives. Establishing a finite element model of the cervical spine is one of the methods for studying cervical spondylosis. MRI (Magnetic Resonance Imaging) still has certain difficulties in transitioning from human imaging to establishing muscle models suitable for finite element analysis. Medical software provides specific morphologies and can generate muscle finite element models. Additionally, there is little research on the static analysis of cervical spine finite element models with solid muscle. Purpose A new method is proposed for establishing a finite element model of the cervical spine based on CT (Computed Tomography) data and medical software, and the model’s effectiveness is validated. Human movement characteristics based on the force distribution in various parts are analyzed and predicted. Methods The muscle model is reconstructed in medical software and a three-dimensional finite element model of the entire cervical spine (C0–C7) is established by combining muscle models with CT vertebral data models. 1.5 Nm of load is applied to the finite element model to simulate the cervical spine movement. Results The finite element model was successfully established, and effectiveness was verified. Stress variations in various parts under six movements were obtained. The effectiveness of the model was basically verified. Conclusion The finite element model of the cervical spine for mechanical analysis can be successfully established by using medical software and CT data. In daily life, the C2–3, C3–4, C4–C5 intervertebral discs, rectus capitis posterior major, longus colli, and obliquus capitis inferior are more prone to injury.

Establishment of a Finite Element Model for the Cervical Spine with Spring Muscle Units

The accelerated pace of modern life has led to an increasing number of people suffering from cervical spondylosis. Traditional research methods for cervical spondylosis are limited by ethical and material constraints, but finite element models can effectively address these issues during the research process. In this paper, a finite element model of C0-C7 vertebrae was reconstructed based on CT scan data, and finite element models of intervertebral discs, ligaments, muscles, and other anatomical structures were added and combined. The reconstructed cervical spine finite element model is highly realistic in shape and has good similarity, making it suitable for cervical spondylosis research.

Cervical Spine Finite Element Models for Healthy Subjects: Development and Validation

Abstract Finite element modeling is a popular method for predicting kinematics and kinetics in spine biomechanics. With the advancement of powerful computational equipment, more detailed finite element models have been developed for the various spine segments. In this study, five detailed finite element models of the cervical spine are developed and validated. The geometric boundaries of the vertebrae are determined from computed tomography (CT) scans of five female subjects. The models include the C2–C7 vertebrae, intervertebral discs, nuclei, endplates, and five major ligaments (anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), ligamentum flavum (LF), interspinous ligament (ISL), and capsular ligament (CL)). The ligaments follow nonlinear stress–strain curves whereas all other parts adopt linear material properties. All the material properties are taken from existing literature. The mesh convergence test is performed under flexion/extension. For flexion/extension motion, a pure moment is applied at the top surface of the odontoid process of the C2 vertebra while nodes at the bottom surface of the C7 vertebra are fixed in all directions. The models are extensively validated in flexion/extension, lateral bending, and axial rotation against experimental and finite element studies in the literature. Intervertebral rotation and range of motion are studied under different loading conditions found in the literature. This research also investigates intersubject variability for the cervical spine among five finite element models from five different subjects. Predicted angular displacements and ranges of motion of the current models are consistent with the literature. The validated models are expected to be applicable to simulate neck-related trauma like whiplash and high-g acceleration, among other scenarios.

Contribution of ligaments to intersegmental stability following type II odontoid fracture.

Purpose: Management of Anderson and D'Alonzo type II odontoid fractures continues to be controversial despite extensive research and increasing prevalence. To the authors' knowledge, the three odontoid ligaments, the alar ligament, the vertical portion of the cruciate ligament, and the transverse ligament, have not been biomechanically examined in type II odontoid fracture in spite of their potential significance in management. Therefore, this study aims to explore the intersegmental rotations of the craniovertebral junction following Anderson and D'Alonzo type II odontoid fracture and various combinations of ligament ruptures. Methods: A validated C0-C7 cervical spine finite element model was employed to address the research objectives. The model was subjected to flexion-extension, lateral bending, and axial rotation under eight distinct injury conditions apart from the intact state. Prescribed rotations were applied to the top of the cranium while the C7 inferior surface was fixed. Rotation-moment data were retrieved from the model. Results: Type II odontoid fracture caused mixed forms of instability considering flexion-extension. In lateral bending, the fracture alone did not have a significant effect, whereas the disruption of ligaments led to moderate rotation increments. Notably, in axial rotation, the fracture was the most crucial factor for stability. Conclusions: Overall, type II odontoid fracture was found to be the main destabilizing element. Nonetheless, the vertical cruciate and the transverse ligament played a modest role in stabilization. The alar ligament provided minimal or no stability. Furthermore, instances were observed where both the vertical cruciate and the transverse ligament were necessary to prevent more instability.

Enhancing the Biofidelity of an Upper Cervical Spine Finite Element Model Within the Physiologic Range of Motion and Its Effect on the Full Ligamentous Neck Model Response.

Contemporary finite element (FE) neck models are developed in a neutral posture; however, evaluation of injury risk for out-of-position impacts requires neck model repositioning to non-neutral postures, with much of the motion occurring in the upper cervical spine (UCS). Current neck models demonstrate a limitation in predicting the intervertebral motions within the UCS within the range of motion, while recent studies have highlighted the importance of including the tissue strains resulting from repositioning FE neck models to predict injury risk. In the current study, the ligamentous cervical spine from a contemporary neck model (GHBMC M50 v4.5) was evaluated in flexion, extension, and axial rotation by applying moments from 0 to 1.5 N·m in 0.5 N·m increments, as reported in experimental studies and corresponding to the physiologic loading of the UCS. Enhancements to the UCS model were identified, including the C0-C1 joint-space and alar ligament orientation. Following geometric enhancements, an analysis was undertaken to determine the UCS ligament laxities, using a sensitivity study followed by an optimization study. The ligament laxities were optimized to UCS-level experimental data from the literature. The mean percent difference between UCS model response and experimental data improved from 55% to 23% with enhancements. The enhanced UCS model was integrated with a ligamentous cervical spine (LS) model and assessed with independent experimental data. The mean percent difference between the LS model and the experimental data improved from 46% to 35% with the integration of the enhanced UCS model.

Biomechanical Analysis of 3-Level Anterior Cervical Discectomy and Fusion Under Physiologic Loads Using a Finite Element Model

ObjectivePseudarthrosis and adjacent segment degeneration (ASD) are 2 common complications after multilevel anterior cervical discectomy and fusion (ACDF). We aim to identify the potential biomechanical factors contributing to pseudarthrosis and ASD following 3-level ACDF using a cervical spine finite element model (FEM). MethodsA validated cervical spine FEM from C2 to C7 was used to study the biomechanical factors in cervical spine intervention. The FEM model was used to simulate a 3-level ACDF with intervertebral spacers and anterior cervical plating with screw fixation from C4 to C7. The model was then constrained at the inferior nodes of the T1 vertebra, and physiological loads were applied at the top vertebra. The pure moment load of 2 Nm was applied in flexion, extension, and lateral bending. A follower axial force of 75 N was applied to reproduce the weight of the cranium and muscle force, was applied using standard procedures. The motion-controlled hybrid protocol was utilized to comprehend the adjustments in the spinal biomechanics. ResultsOur cervical spine FEM demonstrated that the cranial adjacent level (C3–4) had significantly more increase in range of motion (ROM) (+90.38%) compared to the caudal adjacent level at C7–T1 (+70.18%) after C4–7 ACDF, indicating that the cranial adjacent level has more compensatory increase in ROM than the caudal adjacent level, potentially predisposing it to earlier ASD. Within the C4–7 ACDF construct, the C6–7 level had the least robust fixation during fixation compared to C4–5 and C5–6, as reflected by the smallest reduction in ROM compared to intact spine (-71.30% vs. -76.36% and -77.05%, respectively), which potentially predisposes the C6–7 level to higher risk of pseudarthrosis. ConclusionBiomechanical analysis of C4–7 ACDF construct using a validated cervical spine FEM indicated that the C3–4 has more compensatory increase in ROM compared to C7–T1, and C6–7 has the least robust fixation under physiological loads. These findings can help spine surgeons to predicate the areas with higher risks of pseudarthrosis and ASD, and thus developing corresponding strategies to mitigate these risks and provide appropriate preoperative counseling to patients.

Numerical Investigation of Spinal Cord Injury After Flexion-Distraction Injuries at the Cervical Spine.

Flexion-distraction injuries frequently cause traumatic cervical spinal cord injury (SCI). Post-traumatic instability can cause aggravation of the secondary SCI during patient care. However, there is little information on how the pattern of disco-ligamentous injury affects the SCI severity and mechanism. This study objective was to analyze how posterior disco-ligamentous injuries affect spinal cord compression and stress and strain patterns in the spinal cord during post-traumatic flexion and extension. A cervical spine finite element model including the spinal cord was used and different combinations of partial or complete intervertebral disc (IVD) rupture and disruption of various posterior ligaments were modeled at C4-C5, C5-C6, or C6-C7. In flexion, complete IVD rupture combined with posterior ligamentous complex rupture was the most severe injury leading to the highest von Mises stress (47-66 kPa), principal strains p1 (0.32-0.41 in white matter) and p3 (-0.78 to -0.96 in white matter) in the spinal cord and the highest spinal cord compression (35-48%). The main post-trauma SCI mechanism was identified as the compression of the anterior white matter at the injured level combined with distraction of the posterior spinal cord during flexion. There was also a concentration of the maximum stresses in the gray matter during post-traumatic flexion. Finally, in extension, the injuries tested had little impact on the spinal cord. The capsular ligament was the most important structure to protect the spinal cord. Its status should be carefully examined during the patient's management.

Biomechanical Analysis of Posterior Ligaments of Cervical Spine and Laminoplasty

Cervical laminoplasty is a valuable procedure for myelopathy but it is associated with complications such as increased kyphosis. The effect of ligament damage during cervical laminoplasty on biomechanics is not well understood. We developed the C2–C7 cervical spine finite element model and simulated C3–C6 double-door laminoplasty. Three models were created (a) intact, (b) laminoplasty-pre (model assuming that the ligamentum flavum (LF) between C3–C6 was preserved during surgery), and (c) laminoplasty-res (model assuming that the LF between C3–C6 was resected during surgery). The models were subjected to physiological loading, and the range of motion (ROM), intervertebral nucleus stress, and facet contact forces were analyzed under flexion/extension, lateral bending, and axial rotation. The maximum change in ROM was observed under flexion motion. Under flexion, ROM in the laminoplasty-pre model increased by 100.2%, 111.8%, and 98.6% compared to the intact model at C3–C4, C4–C5, and C5–C6, respectively. The ROM in laminoplasty-res further increased by 105.2%, 116.8%, and 101.8% compared to the intact model at C3–C4, C4–C5, and C5–C6, respectively. The maximum stress in the annulus/nucleus was observed under left bending at the C4–C5 segment where an increase of 139.5% and 229.6% compared to the intact model was observed for laminoplasty-pre and laminoplasty-res model, respectively. The highest facet contact forces were observed at C4–C5 under axial rotation, where an increase of 500.7% and 500.7% was observed compared to the intact model for laminoplasty-pre and laminoplasty-res, respectively. The posterior ligaments of the cervical spine play a vital role in restoring/stabilizing the cervical spine. When laminoplasty is performed, the surgeon needs to be careful not to injure the posterior soft tissue, including ligaments such as LF.

Load-Sharing and Kinematics of the Human Cervical Spine Under Multi-Axial Transverse Shear Loading: Combined Experimental and Computational Investigation.

The cervical spine experiences shear forces during everyday activities and injurious events yet there is a paucity of biomechanical data characterizing the cervical spine under shear loading. This study aimed to (1) characterize load transmission paths and kinematics of the subaxial cervical spine under shear loading, and (2) assess a contemporary finite element cervical spine model using this data. Subaxial functional spinal units (FSUs) were subjected to anterior, posterior, and lateral shear forces (200 N) applied with and without superimposed axial compression preload (200 N) while monitoring spine kinematics. Load transmission paths were identified using strain gauges on the anterior vertebral body and lateral masses and a disc pressure sensor. Experimental conditions were simulated with cervical spine finite element model FSUs (GHBMC M50 version 5.0). The mean kinematics, vertebral strains, and disc pressures were compared to experimental results. The shear force-displacement response typically demonstrated a toe region followed by a linear response, with higher stiffness in anterior shear relative to lateral and posterior shear. Compressive axial preload decreased posterior and lateral shear stiffness and increased initial anterior shear stiffness. Load transmission patterns and kinematics suggest the facet joints play a key role in limiting anterior shear while the disc governs motion in posterior shear. The main cervical spine shear responses and trends are faithfully predicted by the GHBMC cervical spine model. These basic cervical spine biomechanics and the computational model can provide insight into mechanisms for facet dislocation in high severity impacts, and tissue distraction in low severity impacts.

Development, validation, and application of ligamentous cervical spinal segment C6-C7 of a six-year-old child and an adult

Background and objectiveThe cervical spine is one of the primary regions that is easily injured in traffic accidents. Although adult cervical spine finite element models have been widely adopted to investigate the cervical injury, few efforts have been made with respect to the development and application of FE models of the pediatric cervical spine, especially that of a six-year-old child. The objective of this study is to develop and validate high quality cervical spinal segment C6-C7 FE models of a six-year-old child and an adult, and to further investigate the differences of C6-C7 between the child and adult under different loading conditions. MethodsThe cervical spinal segment C6-C7 FE models were developed by a structured multiblock method, and were verified under flexion, extension, axial rotation, and lateral bending conditions. The validated models were used to investigate the differences of C6-C7 between the child and adult under different loading conditions. ResultsThe global angular displacement of C6-C7, the ligament elongation ratio, and the maximum effective strain of annulus fibrosus of the child were obviously larger than those of the adult under the same loading conditions. Regarding the loading forms, the flexion angular displacement of C6-C7 of the child was obviously larger than those of the extension and lateral bending, while for the adult cervical segment C6-C7, no obvious differences existed. The elongation ratio of different ligaments was highly dependent on the types of loadings. The maximum effective strain of annulus fibrosus under flexion, extension and lateral bending loads occurred at the compressive region of the front, rear, and one compressive lateral side, in which the annulus fibrosus was more susceptible to injury under the lateral bending condition, compared with those of the flexion and extension conditions. ConclusionsBoth the developed child and adult cervical spinal segment C6-C7 FE models exhibited high biofidelity. The responses (angular displacement, the ligament elongation ratio, and the maximum effective strain of annulus fibrosus) of the child and adult are dependent on the loading types, and the responses of the child were obviously larger than those of the adult under the same loading conditions.

Rear-Impact Neck Whiplash: Role of Head Inertial Properties and Spine Morphological Variations on Segmental Rotations.

Whiplash injuries continue to be a concern in low-speed rear impact. This study was designed to investigate the role of variations in spine morphology and head inertia properties on cervical spine segmental rotation in rear-impact whiplash loading. Vertebral morphology is rarely considered as an input parameter in spine finite element (FE) models. A methodology toward considering morphological variations as input parameters and identifying the influential variations is presented in this paper. A cervical spine FE model, with its morphology parametrized using mesh morphing, was used to study the influence of disk height, anteroposterior vertebral depth, and segmental size, as well as variations in head mass, moment of inertia, and center of mass locations. The influence of these variations on the characteristic S-curve formation in whiplash response was evaluated using the peak C2-C3 flexion marking the maximum S-curve formation and time taken for the formation of maximum S-curve. The peak C2-C3 flexion in the S-curve formation was most influenced by disk height and vertebral depth, followed by anteroposterior head center of mass location. The time to maximum S-curve was most influenced by the anteroposterior location of head center of mass. The influence of gender-dependent variations, such as the vertebral depth, suggests that they contribute to the greater segmental rotations observed in females resulting in different S-curve formation from men. These results suggest that both spine morphology and head inertia properties should be considered to describe rear-impact responses.

Development of a 3-y-old Pediatric Cervical Spine Finite Element Model

A 3-year-old pediatric cervical spine finite element (FE) model with detailed anatomical and material properties was developed and validated against cadaver tests under both quasi-static loadings. First, bone geometry was reconstructed based on high-resolution computed tomography (CT) scans, and elastic-plastic material was defined to simulate the cortical and cancellous bones. To simulate various ligament tears during dynamic tensile, ligament failure was defined using force versus displacement curves, which had a sigmoidal shape governed by three control points. To better represent the complicated structure of the disc, nucleus pulposus, annulus fibrosus substrate and four pairs of reinforced fiber lamina, intervertebral discs were defined using composite materials combined with viscoelastic material, hill foam material and four pairs of reinforced fiber lamina, respectively. This FE model could be utilized in prediction of cervical spine fracture, ligament and disc tear underlying pediatric cervical injuries.

Cervical spine morphology and ligament property variations: A finite element study of their influence on sagittal bending characteristics

Cervical spine finite element models reported in biomechanical literature usually represent a static morphology. Not considering morphology as a model parameter limits the predictive capabilities for applications in personalized medicine, a growing trend in modern clinical practice. The objective of the study was to investigate the influence of variations in spinal morphology on the flexion-extension responses, utilizing mesh-morphing-based parametrization and metamodel-based sensitivity analysis. A C5-C6 segment was used as the baseline model. Variations of intervertebral disc height, facet joint slope, facet joint articular processes height, vertebral body anterior-posterior depth, and segment size were parametrized. In addition, material property variations of ligaments were considered for sensitivity analysis. The influence of these variations on vertebral rotation and forces in the ligaments were analyzed. The disc height, segmental size, and body depth were found to be the most influential (in the cited order) morphology variations; while among the ligament material property variations, capsular ligament and ligamentum flavum influenced vertebral rotation the most. Changes in disc height influenced forces in the posterior ligaments, indicating that changes in the anterior load-bearing column of the spine could have consequences on the posterior column. A method to identify influential morphology variations is presented in this work, which will help automation efforts in modeling to focus on variations that matter. This study underscores the importance of incorporating influential morphology parameters, easily obtained through computed tomography/magnetic resonance images, to better predict subject-specific biomechanical responses for applications in personalized medicine.

Strain behavior of malaligned cervical spine implanted with metal-on-polyethylene, metal-on-metal, and elastomeric artificial disc prostheses – A finite element analysis

BackgroundPostoperative alterations in cervical spine curvature (i.e. loss of lordotic angle) are frequently observed following total disc replacement surgery. However, it remains unclear whether such changes in lordotic angle are due to preoperative spinal deformities and/or prostheses design limitations. The objective of the study is to investigate strain and segmental biomechanics of the malaligned cervical spine following total disc replacement. MethodsThree disc prostheses were chosen, namely a metal-on-polyethylene, a metal-on-metal, and an elastomeric prosthesis, which feature different geometrical and material design characteristics. All discs were modelled and implanted into multi-segmental cervical spine finite element model (C3-C7) with normal, straight and kyphotic alignments. Comparative analyses were performed by using a hybrid protocol. FindingsThe results indicated that as the spine loses lordotic alignment, the prosthesis with elastomeric core tends to produce significantly larger flexion range of motion (difference up to 6.1°) than metal-on-polyethylene and metal-on-metal prostheses. In contrast, when the treated spine had normal lordotic alignment, the range of motion behaviors of different prostheses are rather similar (difference within 1.9°). Large localized strains up to 84.8% were found with the elastomeric prosthesis, causing a collapsed anterior disc space under flexion loads. InterpretationChanges in cervical spinal alignments could significantly affect the surgical-level range of motion behaviors following disc arthroplasty; the in situ performance was largely dependent on the designs of the artificial disc devices in particular to the material properties.

Development and Tensile Investigation of a 3-year-old Cervical Spine Finite Element Model

A 3-year-old cervical spine finite element (FE) model with detailed anatomical and material properties was developed and validated against cadaver tests under dynamic loadings. First, the bone geometry was reconstructed based on high-resolution computed tomography (CT) scans, and the elastic-plastic material was defined to simulate the cortical and cancellous bones. Second, to simulate various ligament tears during dynamic tensile, ligaments failure were defined using force versus displacement curves, which had a sigmoidal shape governed by three control point. To better represent complicated structure of disc, such as nucleus pulposus, annulus fibrosus substrate and four pairs of reinforced fiber lamina, the intervertebral discs were defined using composite materials which combined by viscoelastic material, hill foam material and four pairs of reinforced fiber lamina, respectively. Finally, dynamic tensile experiments in C4-C5 and C0-C7 were used to validate the dynamic ultimate force and displacement of the 3-year-old cervical FE model, revealing that this FE model is capable of predicting intervertebral disc injury and ligament tear. This FE model will contribute to a better understanding of the mechanisms underlying pediatric cervical injuries.

Incorporating ligament laxity in a finite element model for the upper cervical spine

Background ContextPredicting physiological range of motion (ROM) using a finite element (FE) model of the upper cervical spine requires the incorporation of ligament laxity. The effect of ligament laxity can be observed only on a macro level of joint motion and is lost once ligaments have been dissected and preconditioned for experimental testing. As a result, although ligament laxity values are recognized to exist, specific values are not directly available in the literature for use in FE models. PurposeThe purpose of the current study is to propose an optimization process that can be used to determine a set of ligament laxity values for upper cervical spine FE models. Furthermore, an FE model that includes ligament laxity is applied, and the resulting ROM values are compared with experimental data for physiological ROM, as well as experimental data for the increase in ROM when a Type II odontoid fracture is introduced. Design/SettingThe upper cervical spine FE model was adapted from a 50th percentile male full-body model developed with the Global Human Body Models Consortium (GHBMC). FE modeling was performed in LS-DYNA and LS-OPT (Livermore Software Technology Group) was used for ligament laxity optimization. MethodsOrdinate-based curve matching was used to minimize the mean squared error (MSE) between computed load-rotation curves and experimental load-rotation curves under flexion, extension, and axial rotation with pure moment loads from 0 to 3.5 Nm. Lateral bending was excluded from the optimization because the upper cervical spine was considered to be primarily responsible for flexion, extension, and axial rotation. Based on recommendations from the literature, four varying inputs representing laxity in select ligaments were optimized to minimize the MSE. Funding was provided by the Natural Sciences and Engineering Research Council of Canada as well as GHMBC. The present study was funded by the Natural Sciences and Engineering Research Council of Canada to support the work of one graduate student. There are no conflicts of interest to be reported. ResultsThe MSE was reduced to 0.28 in the FE model with optimized ligament laxity compared with an MSE 0f 4.16 in the FE model without laxity. In all load cases, incorporating ligament laxity improved the agreement between the ROM of the FE model and the ROM of the experimental data. The ROM for axial rotation and extension was within one standard deviation of the experimental data. The ROM for flexion and lateral bending was outside one standard deviation of the experimental data, but a compromise was required to use one set of ligament laxity values to achieve a best fit to all load cases. Atlanto-occipital motion was compared as a ratio to overall ROM, and only in extension did the inclusion of ligament laxity not improve the agreement. After a Type II odontoid fracture was incorporated into the model, the increase in ROM was consistent with experimental data from the literature. ConclusionsThe optimization approach used in this study provided values for ligament laxities that, when incorporated into the FE model, generally improved the ROM response when compared with experimental data. Successfully modeling a Type II odontoid fracture showcased the robustness of the FE model, which can now be used in future biomechanics studies.

Development and validation of a C0-C7 cervical spine finite element model

A finite element model (FEM) of human C0-C7 cervical spine has been developed as a baseline to study the biomechanical factors in spinal surgical intervention. To accurately simulate the anisotropic properties, the intervertebral disc was divided into nucleus, annulus matrix and annulus fiber, and it was simulated with viscoelastic and fabric material models. The nonlinear force-displacement curves of ligament experiments were implemented to simulate the elastic zone and neutral zone at low loads. The model was validated with experimental data on range of motion (ROM) for normal, non-degenerated cervical spines tested in flexion and extension, lateral bending, and axial rotation at loads of 0.33, 0.5, 1.0, 1.5, and 2.0 Nm, and intra-discal pressure (IDP) was validated against experiment data at loads of 2Nm and 5Nm. For lateral bending and axial rotation, the model was well within in vitro experimental standard deviation corridors for the whole load range. For extension and flexion, however, the error index of C3-C4, C4-C5, C5-C6 flexion were 0.268, 0.03, 0.124 and the C6-C7 extension was 0.046 respectively. The IDP result was in well agreement with the experiments. These results indicated the C0-C7 cervical spine model was biofidelic for static simulation of these motions.

A Female Ligamentous Cervical Spine Finite Element Model Validated for Physiological Loads.

Mathematical cervical spine models allow for studying of impact loading that can cause whiplash associated disorders (WAD). However, existing models only cover the male anthropometry, despite the female population being at a higher risk of sustaining WAD in automotive rear-end impacts. The aim of this study is to develop and validate a ligamentous cervical spine intended for biomechanical research on the effect of automotive impacts. A female model has the potential to aid the design of better protection systems as well as improve understanding of injury mechanisms causing WAD. A finite element (FE) mesh was created from surface data of the cervical vertebrae of a 26-year old female (stature 167 cm, weight 59 kg). Soft tissues were generated from the skeletal geometry and anatomical literature descriptions. Ligaments were modeled with nonlinear elastic orthotropic membrane elements, intervertebral disks as composites of nonlinear elastic bulk elements, and orthotropic anulus fibrosus fiber layers, while cortical and trabecular bones were modeled as isotropic plastic-elastic. The model has geometrical features representative of the female cervical spine-the largest average difference compared with published anthropometric female data was the vertebral body depth being 3.4% shorter for the model. The majority the cervical segments compare well with respect to biomechanical data at physiological loads, with the best match for flexion-extension loads and less biofidelity for axial rotation. An average female FE ligamentous cervical spine model was developed and validated with respect to physiological loading. In flexion-extension simulations with the developed female model and an existing average male cervical spine model, a greater range of motion (ROM) was found in the female model.

Impact of Cervical Artificial Disc Implantation on the Biomechanical Function of Adjacent Segments

The range of movement(ROM) of adjacent segments and the change of intervertebral disc stress after implanting artificial cervical disc are investigated. The contact problem for bio-modeling is introduced. A normal cervical spine finite element model is proposed. The bone graft and fusion between C5 and C6 and C5/6 artificial disc implantation were simulated. The range of movement on adjacent segment and the change of intervertebral disc’s stress in such two cases are analyzed. Computational results show that the model includes the ligaments, joint capsule and other soft tissue structures, which is real, fine and high accuracy. When the adjacent intervertebral ROM was increased after interbody fusion surgery, the stress of corresponding intervertebral disc was increased obviously and the stress of upper segment of nucleus pulposus and annulus fibrosus were also increased about 70% ,besides the next-bit segments was increased about 40%. There were no differences among cervical spine ROM except extension (p> 0.05) after the implantation of artificial disc, and the stress on adjacent segments was increased less than 10%. The implantation of artificial cervical disc can release the stress on adjacent segments in a certain extent, and resume cervical activities at the same time.

Development and Validation of a 10-Year-Old Child Ligamentous Cervical Spine Finite Element Model

Although a number of finite element (FE) adult cervical spine models have been developed to understand the injury mechanisms of the neck in automotive related crash scenarios, there have been fewer efforts to develop a child neck model. In this study, a 10-year-old ligamentous cervical spine FE model was developed for application in the improvement of pediatric safety related to motor vehicle crashes. The model geometry was obtained from medical scans and meshed using a multi-block approach. Appropriate properties based on review of literature in conjunction with scaling were assigned to different parts of the model. Child tensile force–deformation data in three segments, Occipital-C2 (C0–C2), C4–C5 and C6–C7, were used to validate the cervical spine model and predict failure forces and displacements. Design of computer experiments was performed to determine failure properties for intervertebral discs and ligaments needed to set up the FE model. The model-predicted ultimate displacements and forces were within the experimental range. The cervical spine FE model was validated in flexion and extension against the child experimental data in three segments, C0–C2, C4–C5 and C6–C7. Other model predictions were found to be consistent with the experimental responses scaled from adult data. The whole cervical spine model was also validated in tension, flexion and extension against the child experimental data. This study provided methods for developing a child ligamentous cervical spine FE model and to predict soft tissue failures in tension.