scholarly journals The importance of intervertebral disc material model on the prediction of mechanical function of the cervical spine

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Amin Komeili ◽  
Akbar Rasoulian ◽  
Fatemeh Moghaddam ◽  
Marwan El-Rich ◽  
Le Ping Li
Keyword(s):  
Intervertebral Disc ◽  
Mechanical Response ◽  
Fluid Pressure ◽  
Material Model ◽  
Load Sharing ◽  
Disc Height ◽  
Loading Conditions ◽  
Material Models ◽  
Linear Elastic ◽  
Disc Material

Abstract Background Linear elastic, hyperelastic, and multiphasic material constitutive models are frequently used for spinal intervertebral disc simulations. While the characteristics of each model are known, their effect on spine mechanical response requires a careful investigation. The use of advanced material models may not be applicable when material constants are not available, model convergence is unlikely, and computational time is a concern. On the other hand, poor estimations of tissue’s mechanical response are likely if the spine model is oversimplified. In this study, discrepancies in load response introduced by material models will be investigated. Methods Three fiber-reinforced C2-C3 disc models were developed with linear elastic, hyperelastic, and biphasic behaviors. Three different loading modes were investigated: compression, flexion and extension in quasi-static and dynamic conditions. The deformed disc height, disc fluid pressure, range of motion, and stresses were compared. Results Results indicated that the intervertebral disc material model has a strong effect on load-sharing and disc height change when compression and flexion were applied. The predicted mechanical response of three models under extension had less discrepancy than its counterparts under flexion and compression. The fluid-solid interaction showed more relevance in dynamic than quasi-static loading conditions. The fiber-reinforced linear elastic and hyperelastic material models underestimated the load-sharing of the intervertebral disc annular collagen fibers. Conclusion This study confirmed the central role of the disc fluid pressure in spinal load-sharing and highlighted loading conditions where linear elastic and hyperelastic models predicted energy distribution different than that of the biphasic model.

DYNAMIC RESPONSES OF INTERVERTEBRAL DISC DURING STATIC CREEP AND DYNAMIC CYCLIC LOADING: A PARAMETRIC POROELASTIC FINITE ELEMENT ANALYSIS

2013 ◽  
Vol 25 (01) ◽  
pp. 1350013 ◽  
Author(s):  
Mohammad Nikkhoo ◽  
Mohammad Haghpanahi ◽  
Mohamad Parnianpour ◽  
Jaw-Lin Wang
Keyword(s):  
Finite Element ◽  
Elastic Modulus ◽  
Intervertebral Disc ◽  
Pore Pressure ◽  
Void Ratio ◽  
Disc Height ◽  
Poisson's Ratio ◽  
Height Loss ◽  
Loading Frequency ◽  
Loading Conditions

Low back pain is a common reason for activity limitation in people younger than 45 years old, and was proved to be associated with heavy physical works, repetitive lifting, impact, stationary work postures and vibrations. The study of load transferring and the loading condition encountered in spinal column can be simulated by finite element models. The intervertebral disc is a structure composed of a porous material. Many physical models were developed to simulate this phenomenon. The confounding effects of poroelastic properties and loading conditions on disc mechanical responses are, nevertheless, not cleared yet. The objective of this study was to develop an axisymmetric poroelastic finite element model of intervertebral disc and use it to investigate the confounding effect of material properties and loading conditions on the disc deformation and pore pressure. An axisymmetric poroelastic model of human lumbar L4–L5 motion segment was developed. The model was validated by comparing the height loss and intradiscal pressure of the L4–L5 intervertebral disc with in vitro cadaveric studies. The effect of permeability, void ratio, elastic modulus, and Poisson's ratio on disc height and pore pressure was investigated for the following three loading conditions: (1) 1334 N creep loading, (2) peak-to-peak, 1000-to-1600 N, 1 Hz cyclic loading, and (3) same loading magnitude, but at 5 Hz loading frequency. The disc height loss and pore pressure of the three loading conditions were analyzed. The predictions of the disc height loss and intradiscal pressure of the current FE model are well comparable with the results of in vitro cadaveric studies. After model validation, the parametric study of disc poroelastic properties on the disc mechanical responses shows that the increase of permeability and void ratio increases the disc height loss and decreases the pore pressure, and these effects are sensitive to external loading frequency. Higher elastic modulus reduces the disc deformation and the pore pressure, but this reduction is not sensitive to the loading frequency. The effect of Poisson's ratio on disc height loss and pore pressure is negligible. In conclusion, the hydraulic permeability describes the fluid flow capability within tissue matrix which has a higher sensitivity on the saturation time for disc deformation and pore pressure. Void ratio directly affects the amount of mobile water within disc and changes time-dependent response of disc. Increase in loading frequency reduces time for fluid inflow and outflow, which fades out the role of permeability and void ratio. Values of elastic modulus and Poisson's ratio, which demonstrates stiffness and bulging capacity, respectively, do not affect the overall dynamic response of disc.

Development of a Biofidelic Material Model for Brain Tissue

2011 ◽  
Author(s):  
Sandeep Kulathu ◽  
David L. Littlefield
Keyword(s):  
Brain Tissue ◽  
Grey Matter ◽  
Mechanical Response ◽  
Constitutive Models ◽  
Material Model ◽  
Small Sample ◽  
Material Models ◽  
Computational Mesh ◽  
Injury Mechanisms ◽  
The Brain

Computational simulations of brain injury mechanisms have advanced to a level of sophistication where in addition to capturing different anatomic regions, the computational mesh is capable of distinguishing white and grey matter in the brain. Brain tissue is typically modeled as an isotropic, viscoelastic material. Experiments have shown that the mechanical response of brain tissue to an external load varies depending on the location from which the tissue is harvested and also the direction of loading. Some researchers have developed anisotropic constitutive models by appealing to the composite material case wherein cylindrical axon fibers are immersed in a cellular matrix. Though such material models have been developed over a small sample, they have not been applied over the entire brain for simulation purposes.

Comparing Predictive Accuracy and Computational Costs for Viscoelastic Modeling of Spinal Cord Tissues

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Nicole L. Ramo ◽  
Kevin L. Troyer ◽  
Christian M. Puttlitz
Keyword(s):  
Experimental Data ◽  
Spinal Cord ◽  
Mechanical Response ◽  
Predictive Accuracy ◽  
Material Model ◽  
Loading Conditions ◽  
Nonlinear Viscoelastic ◽  
Arbitrary Loading ◽  
Linear Viscoelastic ◽  
Viscoelastic Modeling

Abstract The constitutive equation used to characterize and model spinal tissues can significantly influence the conclusions from experimental and computational studies. Therefore, researchers must make critical judgments regarding the balance of computational efficiency and predictive accuracy necessary for their purposes. The objective of this study is to quantitatively compare the fitting and prediction accuracy of linear viscoelastic (LV), quasi-linear viscoelastic (QLV), and (fully) nonlinear viscoelastic (NLV) modeling of spinal-cord-pia-arachnoid-construct (SCPC), isolated cord parenchyma, and isolated pia-arachnoid-complex (PAC) mechanics in order to better inform these judgements. Experimental data collected during dynamic cyclic testing of each tissue condition were used to fit each viscoelastic formulation. These fitted models were then used to predict independent experimental data from stress-relaxation testing. Relative fitting accuracy was found not to directly reflect relative predictive accuracy, emphasizing the need for material model validation through predictions of independent data. For the SCPC and isolated cord, the NLV formulation best predicted the mechanical response to arbitrary loading conditions, but required significantly greater computational run time. The mechanical response of the PAC under arbitrary loading conditions was best predicted by the QLV formulation.

A Comparison of the Human Lumbar Intervertebral Disc Mechanical Response to Normal and Impact Loading Conditions

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
David Jamison ◽  
Marco Cannella ◽  
Eric C. Pierce ◽  
Michele S. Marcolongo
Keyword(s):  
Low Back Pain ◽  
Back Pain ◽  
Intervertebral Disc ◽  
Impact Loading ◽  
High Speed ◽  
Mechanical Response ◽  
Back Injury ◽  
Low Back ◽  
Loading Conditions ◽  
High Incidence

Thirty-four percent of U.S. Navy high speed craft (HSC) personnel suffer from lower back injury and low back pain, compared with 15 to 20% of the general population. Many of these injuries are specifically related to the intervertebral disc, including discogenic pain and accelerated disc degeneration. Numerous studies have characterized the mechanical behavior of the disc under normal physiological loads, while several have also analyzed dynamic loading conditions. However, the effect of impact loads on the lumbar disc—and their contribution to the high incidence of low back pain among HSC personnel—is still not well understood. An ex vivo study on human lumbar anterior column units was performed in order to investigate disc biomechanical response to impact loading conditions. Samples were subjected to a sequence of impact events of varying duration (Δt = 80, 160, 320, 400, 600, 800, and 1000 ms) and the level of displacement (0.2, 0.5, and 0.8 mm), stiffness k, and energy dissipation ΔE were measured. Impacts of Δt = 80 ms saw an 18–21% rise in k and a 3–7% drop in ΔE compared to the 1000 ms baseline, signaling an abrupt change in disc mechanics. The altered disc mechanical response during impact likely causes more load to be transferred directly to the endplates, vertebral bodies, and surrounding soft tissues and can help begin to explain the high incidence of low back pain among HSC operators and other individuals who typically experience similar loading environments. The determination of a “safety range” for impacts could result in a refinement of design criteria for shock mitigating systems on high-speed craft, thus addressing the low back injury problem among HSC personnel.

scholarly journals Finite Element modeling of Mechanical Loading-Pumpkin Peel and flesh

2017 ◽  
Vol 13 (5) ◽  
Author(s):  
Maryam Shirmohammadi ◽  
Prasad KDV Yarlagadda
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Plastic Material ◽  
Material Model ◽  
Mean Square ◽  
Fe Modeling ◽  
Material Models ◽  
Linear Elastic Material ◽  
Error Indicator ◽  
Linear Elastic

Abstract Finite element (FE) models of uniaxial loading of pumpkin peel and flesh tissues were developed and validated using experimental results. The tensile model was developed for both linear elastic and plastic material models, the compression model was developed only with the plastic material model. The outcomes of force versus time curves obtained from FE models followed similar pattern to the experimental curves; however the curve resulted with linear elastic material properties had a higher difference with the experimental curves. The values of predicted forces were determined and compared with the experimental curve. An error indicator was introduced and computed for each case and compared. Additionally, Root Mean Square Error (RMSE) values were also calculated for each model and compared. The results of modeling were used to develop material model for peel and flesh tissues in FE modeling of mechanical peeling of tough skin vegetables. The results presented in this paper are a part of a study on mechanical properties of agricultural tissues focusing on mechanical peeling methods using mathematical, experimental and computational modeling.

Mechanical yield of the lumbar annulus: a possible contributor to instability

2014 ◽  
Vol 21 (4) ◽  
pp. 608-613 ◽  
Author(s):  
Brian D. Stemper ◽  
Jamie L. Baisden ◽  
Narayan Yoganandan ◽  
Barry S. Shender ◽  
Dennis J. Maiman
Keyword(s):  
Lumbar Spine ◽  
Intervertebral Disc ◽  
Mechanical Response ◽  
Facet Joint ◽  
Intervertebral Discs ◽  
Stress And Strain ◽  
Anatomical Region ◽  
Linear Elastic ◽  
Load Carrying ◽  
Ultimate Failure

Object Segmental instability in the lumbar spine can result from a number of mechanisms including intervertebral disc degeneration and facet joint degradation. Under traumatic circumstances, elevated loading may lead to mechanical yield of the annular fibers, which can decrease load-carrying capacity and contribute to instability. The purpose of this study was to quantify the biomechanics of intervertebral annular yield during tensile loading with respect to spinal level and anatomical region within the intervertebral disc. Methods This laboratory-based study incorporated isolated lumbar spine annular specimens from younger and normal or mildly degenerated intervertebral discs. Specimens were quasi-statically distracted to failure in an environmentally controlled chamber. Stress and strain associated with yield and ultimate failure were quantified, as was stiffness in the elastic and postyield regions. Analysis of variance was used to determine statistically significant differences based on lumbar spine level, radial position, and anatomical region of the disc. Results Annular specimens demonstrated a nonlinear response consisting of the following: toe region, linear elastic region, yield point, postyield region, and ultimate failure point. Regional dependency was identified between deep and superficial fibers. Mechanical yield was evident prior to ultimate failure in 98% of the specimens and occurred at approximately 80% and 74% of the stress and strain, respectively, to ultimate failure. Fiber modulus decreased by 34% following yield. Conclusions Data in this study demonstrated that yielding of intervertebral disc fibers occurs relatively early in the mechanical response of the tissues and that stiffness is considerably decreased following yield. Therefore, yielding of annular fibers may result in decreased segmental stability, contributing to accelerated degeneration of bony components and possible idiopathic pain.

Stability Analysis of Arteries Under Torsion

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Nir Emuna ◽  
David Durban
Keyword(s):  
Mechanical Response ◽  
Twist Angle ◽  
Fluid Pressure ◽  
Geometrical Parameters ◽  
Prediction Errors ◽  
Key Factors ◽  
Stability Margins ◽  
Linear Elastic ◽  
Twist Rate ◽  
Experimental Approaches

Abstract Vascular tortuosity may impede blood flow, occlude the lumen, and ultimately lead to ischemia or even infarction. Mechanical loads like blood pressure, axial force, and also torsion are key factors participating in this complex mechanobiological process. The available studies on arterial torsion instability followed computational or experimental approaches, yet single available theoretical study had modeled the artery as isotropic linear elastic. This paper aim is to validate a theoretical model of arterial torsion instability against experimental data. The artery is modeled as a single-layered, nonlinear, hyperelastic, anisotropic solid, with parameters calibrated from experiment. Linear bifurcation analysis is then performed to predict experimentally measured stability margins. Uncertainties in geometrical parameters and in measured mechanical response were considered. Also, the type of rate (incremental) boundary conditions (RBCs) impact on the results was examined (e.g., dead load, fluid pressure). The predicted critical torque and twist angle followed the experimentally measured trends. The closest prediction errors in the critical torque and twist rate were 22% and 67%, respectively. Using the different RBCs incurred differences of up to 50% difference within the model predictions. The present results suggest that the model may require further improvements. However, it offers an approach that can be used to predict allowable twist levels in surgical procedures (like anastomosis and grafting) and in the design of stents for arteries subjected to high torsion levels (like the femoropopliteal arteries). It may also be instructive in understanding biomechanical processes like arterial tortuosity, kinking, and coiling.

scholarly journals Fatigue Crack Growth Analysis with Extended Finite Element for 3D Linear Elastic Material

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 397
Author(s):  
Yahya Ali Fageehi
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Propagation ◽  
Crack Growth ◽  
Mixed Mode ◽  
Propagation Path ◽  
Loading Conditions ◽  
Extended Finite Element ◽  
Linear Elastic

This paper presents computational modeling of a crack growth path under mixed-mode loadings in linear elastic materials and investigates the influence of a hole on both fatigue crack propagation and fatigue life when subjected to constant amplitude loading conditions. Though the crack propagation is inevitable, the simulation specified the crack propagation path such that the critical structure domain was not exceeded. ANSYS Mechanical APDL 19.2 was introduced with the aid of a new feature in ANSYS: Smart Crack growth technology. It predicts the propagation direction and subsequent fatigue life for structural components using the extended finite element method (XFEM). The Paris law model was used to evaluate the mixed-mode fatigue life for both a modified four-point bending beam and a cracked plate with three holes under the linear elastic fracture mechanics (LEFM) assumption. Precise estimates of the stress intensity factors (SIFs), the trajectory of crack growth, and the fatigue life by an incremental crack propagation analysis were recorded. The findings of this analysis are confirmed in published works in terms of crack propagation trajectories under mixed-mode loading conditions.

Linear elastic and hyperelastic studies of equine hoof mechanical response at different hydration levels

2021 ◽  
pp. 104622
Author(s):  
Naeim Akbari Shahkhosravi ◽  
Soheil Gohari ◽  
Amin Komeili ◽  
Colin Burvill ◽  
Helen Davies
Keyword(s):  
Mechanical Response ◽  
Linear Elastic ◽  
Equine Hoof

scholarly journals A Scoring System for Anterior Longitudinal Ligament Ossification of the Lumbar Spine in Diffuse Idiopathic Skeletal Hyperostosis: Relationship Between the Extent of Ligament Ossification and the Range of Motion

2021 ◽  
pp. 219256822199668
Author(s):  
Yusuke Murakami ◽  
Tadao Morino ◽  
Masayuki Hino ◽  
Hiroshi Misaki ◽  
Hiroshi Imai ◽  
...  
Keyword(s):  
Lumbar Spine ◽  
Intervertebral Disc ◽  
Range Of Motion ◽  
Scoring System ◽  
Diffuse Idiopathic Skeletal Hyperostosis ◽  
Disc Height ◽  
Rater Reliability ◽  
Canal Stenosis ◽  
Intervertebral Disc Height ◽  
The Relationship

Study Design: Retrospective observational study. Objective: To investigate the relationship between the extent of ligament ossification and the range of motion (ROM) of the lumbar spine and develop a new scoring system. Methods: Forty-three patients (30 men and 13 women) with lumbar spinal canal stenosis who underwent decompression from January to December 2018. Ligament ossification at L1/2 to L5/S was assessed on plain X-ray (Xp) and computed tomography (CT) using a modified Mata scoring system (0 point: no ossification, 1 point: ossification of less than half of the intervertebral disc height, 2 points: ossification of half or more of the intervertebral disc height, 3 points: complete bridging), and the intra-rater and inter-rater reliability of the scoring was assessed. The relationship of the scores with postoperative lumbar ROM was investigated. Result: Intra-rater reliability was high (Cronbach’s α was 0.74 for L5/S on Xp but 0.8 or above for other sections), as was inter-rater reliability (Cronbach’s α was 0.8 or above for all the segments). ROM significantly decreased as the score increased (scores 1 to 2, and 2 to 3). A significant moderate negative correlation was found between the sum of the scores at L1/2-L5/S and the ROM at L1-S (ρ = − 0.4493, P = 0.025). Conclusion: Our scoring system reflects lumbar mobility and is reproducible. It is effective for assessing DISH in fractures and spinal conditions, and monitoring effects on treatment outcomes and changes over time.

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