Behavior Of Intervertebral Disc Research Articles

Effect of fiber volume and material property and nucleus pulposus area on intervertebral disc mechanical behavior

The material properties and volume proportion of the fibers as well as the cross-sectional area proportion of nucleus pulposus vary greatly in different studies. The effect of these factors on the mechanical behavior of intervertebral discs (IVDs) are uncertain. The IVDs finite element models with different parameters were created to investigate the pressure, height, rotation, stress, and strain of the IVDs under loads: pure compression, rotation after compression or axial moment after compression. The results showed that the material properties of fibers had great impact on the mechanical behavior of IVDs, especially on the rotation angle. When the fiber volume ratio was small, its changes had a significant impact on the rotation angle of the IVDs. The area proportions of nucleus pulposus had relatively little effect on the mechanical behavior of IVDs. The IVDs rotation should be observed when validating the model. By adjusting the elastic modulus or volume ratio of fibers within a reasonable range, a model that could simulate the mechanical behavior of normal IVDs could be obtained. It was reasonable to make the area proportion of nucleus pulposus within 25%-50% for the IVDs finite element model. This study provides guidance and reference for finite element modeling of the IVDs and the investigation of the IVDs degeneration mechanism.

Analysis of the Biomechanical Behavior of the Intervertebral Discs by Modeling Three-Phase Finite Elements

Intervertebral discs act as a shock absorber to counteract the blows to the spine. These elements have the ability to deform when applied pressure, thus reducing the intensity of impacts. The main shape of discs is spherical when not under pressure; but when they are placed between the vertebrae, they expand under the pressure. One of the important functions of intervertebral discs is to facilitate movements in the spine In order to study biological mechanics as one of the engineering infrastructures, in this paper, the combined modeling of finite element intervertebral discs as a saturated porous soft tissue is discussed. First, according to the continuum mechanics, the mathematical model is extracted and then the finite element model is prepared by ANSYS program package. Based on the different loads according to the available medical information, the biomechanical behavior of the disk was investigated. This model can be used to investigate the behavior of intervertebral discs in patients before or after surgery. In this paper, in addition to the mathematical model, the mechanical behavior of the disk and the stress distribution under different loads were investigated.

Research progress in creep characteristics of lumbar intervertebral disc

To summarize the research progress in creep characteristics of lumbar intervertebral disc. The relevant literature at home and abroad was systematically searched. Then, the concept and structural basis of lumbar disc creep, the description of creep characteristics, and the latest progress of its influencing factors were summarized and analyzed. The intervertebral disc is viscoelastic. After loading, the deformation increases with time. However, the degree of increase is not linear with time. That is creep, which plays an important role in buffering the load generated by human activities and absorbing energy in order to maintain stable movement of the spine. Both experimental and simulation studies can well describe the creep behavior of intervertebral disc. Various models including standard linear solid model and corresponding constitutive equations can quantify and compare the creep characteristics, which can be obviously changed by the degeneration of intervertebral disc and the mode of loading stress. Creep is an important mechanical properties of intervertebral discs, and an in-depth understanding of the creep characteristics of lumbar intervertebral discs is of great guiding significance for the intervention and treatment of low back pain.

Effect of Strain Rates on Failure of Mechanical Properties of Lumbar Intervertebral Disc Under Flexion.

ObjectiveTo evaluate the strain‐rate‐dependent viscoelastic properties of the intervertebral disc by in vitro experiments.MethodThe biomechanical experiments were conducted from September 2019 to December 2019. The lumbar spines of sheep were purchased within 4–6 hours from the local slaughterhouse, and the intervertebral disc samples were divided into three groups. In rupture group, the samples were used to test the mechanical behavior of the intervertebral disc rupture at different strain rates. In fatigue injury group, the samples were used to test the mechanical behavior of fatigue injury on the intervertebral disc under different strain rates. In internal displacement group, the samples were used to test the internal displacement distribution of the intervertebral disc at different strain rates by applying an optimized digital image correlation (DIC) technique.ResultsBoth the yielding and cracking phenomenon occurs at fast and medium loading rates, while only the yielding phenomenon occurs at a slow loading rate. The yield stress, compressive strength, and elastic modulus all increase with the increase of the strain rate, while the yield strain decreases with the increase of the strain rate. The logarithm of the elastic modulus in the intervertebral disc is approximately linear with the logarithm of the strain rate under different strain rates. Both before and after fatigue loading, the stiffness in the loading and unloading curves of the intervertebral disc is inconsistent, forming a hysteresis loop, which is caused by the viscoelastic effect. The strain rate has no significant effect on the internal displacement distribution of the intervertebral disc. Based on the experimental data, the constitutive relationship of the intervertebral disc at different strain rates is obtained. The fitting curves are well coupled with the experimental data, while the fitting parameters are approximately linear with the logarithm of the strain rate.ConclusionsThese experiments indicate that the strain rate has a significant effect on the mechanical behavior of the intervertebral disc rupture and fatigue injury, while the constitutive equation can predict the rate‐dependent mechanical behavior of lumbar intervertebral disc under flexion very well. These results have important theoretical guiding significance for preventing lumbar disc herniation in daily life.

Ratcheting Behavior of Intervertebral Discs Under Cyclic Compression: Experiment and Prediction.

ObjectiveTo evaluate the ratcheting behavior of intervertebral discs (IVD) by experiments and theoretical study.MethodThe lumbar spines of sheep were obtained at a local slaughterhouse, and the IVD was processed with upper and lower vertebral bodies (about 5 mm) to ensure the mechanical state of the IVD in situ. The ratcheting tests of uniaxial cyclic compression loading for disc samples is carried out using the Electronic Universal Fatigue Testing System at room temperature. The effects of different stress variations, stress rates, as well as different segments on ratcheting behavior of discs were investigated.ResultsThe ratcheting strain evolution of lumbar IVD include stages of sharp increase and asymptotic stability. Both the ratcheting strain and ratcheting strain rate increase with an increase of stress variation (R = 0.962, P = 0.004) but decrease with an increase of the stress rate (R = −0.876, P = 0.019 ). Compression stiffness increases with an increase of the stress rate (R = 0.964, P = 0.004 ) or stress variation (R = 0.838, P = 0.037). Compared with L5 – 6, the L6 – 7 disc showed less ratcheting strain (P = 0.04 ), indicating that the disc at this segment was more resistant to the impact of the ratcheting cycle. In addition, ratcheting strain evolution was predicted using a ratcheting evolution constitutive equation, and the predicted results were in good agreement with experimental data.ConclusionsThe ratcheting behavior occurs in IVD, and this cumulative deformation is consistent with the general ratcheting behavior. The constitutive equation can predict the ratcheting strain evolution of IVD very well. These results are of great significance for the analysis of defects and the development of repair in IVD.

Finite element investigation of the intervertebral disc behaviour

Cervical disc injury due to impact has been observed in clinical and biomechanical investigations; however, there is a lack of data that helps to elucidate the mechanisms of disc injury during thes...

Study of the biomechanical behaviour of structurally stable/unstable motion segments of the sheep spine

AbstractThe effects of damage of intervertebral discs on their biomechanical behaviour and the factors favouring the progression of instability are studied. Healthy and damaged movement segments are analyzed experimentally and numerically. The aim is to represent and predict the effects of tissue damage and changes in the spine by comparison with healthy segments. Since the intervertebral disc acts as a mechanical damper, relaxation tests are performed in addition to pressure experiments. The experiments are carried out in a bioreactor with tempered nutrient solution. A cultivation period in the bioreactor allows detecting cell viability, solute diffusion rates and gene expression of the discs. Numerically, the nonlinear, viscoelastic, anisotropic and diffusion‐dependent behaviour of the intervertebral disc is modelled with the FE‐program Abaqus, using a modular material law as a UMAT subroutine. With the measurement results, the relevant parameters can be determined so that the mechanical behaviour of intervertebral discs can be simulated. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Homogenisation method to capture the non‐linear behaviour of intervertebral discs in multi‐body systems

AbstractThe present contribution is motivated by the desire to compute physiological loads on the intervertebral discs (IVD) of a human lumbar spine during activities like standing, bending and falling. Following this, a mechanical multi‐body system (MBS) is utilised to capture the overall mechanical behaviour of a human, whereas an inhomogeneous, anisotropic, multi‐phasic finite‐element model (FEM) is applied to resolve the resulting field quantities inside an IVD. In order to couple the FEM of the IVD with the numerically diverse MBS, a homogenisation procedure has to be applied such that field quantities can be converted into discrete quantities. In particular, the MBS captures the mechanical behaviour of an IVD using a bushing element, which provides discrete force‐displacement and moment‐rotation relations.The goal of this contribution is to present a homogenisation method for the IVD as well as a possibility to include the homogenised results in the MBS without the need for embedded FE computations in the MBS. Instead, certain deformation modes of the IVD are pre‐computed and represented using a non‐linear constitutive equations. This task becomes even more challenging, as the resulting discrete DOF of a motion segment appear in a coupled fashion due to the structure of the IVD, i. e., a rotation in the sagittal plane triggers a resulting moment and a resulting force. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Resultados a largo plazo de la microdiscectomía lumbar en una población laboralmente activa

In the treatment of the lumbar disc herniaton (LDH) microdiscectomy constitutes one of the standard procedures. In the present study we have analyzed the clinical outcome of the lumbar microdis- cectomy in a series of worker patients who underwent surgery in our service. Retrospective analysis and a 5-year follow up, of a series of 142 patients operated on by means of lumbar microdiscectomy in the 2004-2005 period. The clinical outcome was analyzed according to the "Herron and Turner" outline: pain reduction, use of medical treatment, restriction in the ability to perform physical activities, and return to work. 116 men and 26 women, with an average age of 37.9 and 45.4 years respectively, underwent surgery because of LDH. In the clinical aspect, sciatica was predominant over low back pain in a ratio of three to one. The L5-S1 discal level was operated on in 68.3% of the cases. It was considered that occupational activities gave rise to damage in 107 patients (75.3%). Besides a symptomatic disc, there was an additional injured disc in 44.3% of the cases. An initial unfavourable outcome was seen in 42 patients (33%), 15 of which recovered from in an interval of 3 months, and another fifteen within a one year period. A re-operation was necessa ry in 16 patients because of recurrent lumbar disc herniation (11%). Work reintegration was achieved in 83.3% (119/142) of the cases. After a 5-year follow up, we stated the consistency of the clinical result. We analyzed the intervertebral disc behaviour as regards sex, age, variety of discal herniation, additional disc, outcome and re-operation variables. After the analysis of the type of discal herniation and additional disc we defined three disc injury patterns. We consider microdiscectomy as the technique of choosing for the treatment of recurrence disc herniation. Between the working class, discal injury predominates in young men, as a consequence of the annulus breakage, or an annulus plus posterior longitudinal ligament breakage (traumatic herniae). Frequently it was observed that more than one disc was involved, and a left lateralization.

Simulation of the Lumbar Spine as a Multi-Module Paralel Manipulator

In this paper a simulation of movements of lumbar spine is proposed by using a model with serially connected parallel manipulators. An analysis has been computed for the human spine structure and its movements, in order to simulate the motions and forces that actuate a spine specifically in the lumbar segment. A mechanical model has been designed with available identified parameters of human spine, by using characteristics of parallel manipulators and spring stiffness. This model is suitable to properly simulate the trunk behavior at macroscopic level but also the smooth behavior of intervertebral discs and actuating motions of muscles and tendons. Simulation results for spring actions and joints reaction forces can give an evaluation of the forces that intervertebral discs supports during motions of a real spine.

Simulation of the Lumbar Spine as a Multi-Module Paralel Manipulator

In this paper a simulation of movements of lumbar spine is proposed by using a model with serially connected parallel manipulators. An analysis has been computed for the human spine structure and its movements, in order to simulate the motions and forces that actuate a spine specifically in the lumbar segment. A mechanical model has been designed with available identified parameters of human spine, by using characteristics of parallel manipulators and spring stiffness. This model is suitable to properly simulate the trunk behavior at macroscopic level but also the smooth behavior of intervertebral discs and actuating motions of muscles and tendons. Simulation results for spring actions and joints reaction forces can give an evaluation of the forces that intervertebral discs supports during motions of a real spine.

The elastic fibre network of the human lumbar anulus fibrosus: architecture, mechanical function and potential role in the progression of intervertebral disc degeneration

Elastic fibres are critical constituents of dynamic biological structures that functionally require elasticity and resilience. The network of elastic fibres in the anulus fibrosus of the intervertebral disc is extensive, however until recently, the majority of histological, biochemical and biomechanical studies have focussed on the roles of other extracellular matrix constituents such as collagens and proteoglycans. The resulting lack of detailed descriptions of elastic fibre network architecture and mechanical function has limited understanding of the potentially important contribution made by elastic fibres to healthy disc function and their possible roles in the progression of disc degeneration. In addition, it has made it difficult to postulate what the consequences of elastic fibre related disorders would be for intervertebral disc behaviour, and to develop treatments accordingly. In this paper, we review recent and historical studies which have examined both the structure and the function of the human lumbar anulus fibrosus elastic fibre network, provide a synergistic discussion in an attempt to clarify its potentially critical contribution both to normal intervertebral disc behaviour and the processes relating to its degeneration, and recommend critical areas for future research.

The role of the nucleus pulposus in neutral zone human lumbar intervertebral disc mechanics

To study the effect of denucleation on the mechanical behavior of the human lumbar intervertebral disc through a 2 mm incision, two groups of six human cadaver lumbar spinal units were tested in axial compression, axial rotation, lateral bending and flexion/extension after incremental steps of “partial” denucleation. Neutral zone, range of motion, stiffness, intradiscal pressure and energy dissipation were measured; the results showed that the contribution of the nucleus pulposus to the mechanical behavior of the intervertebral disc was more dominant through the neutral zone than at the farther limits of applied loads and moments.

Identification of Viscoelastic Property of Intervertebral Disc Under Flexion, Extension and Lateral Bending

Viscoelastic behavior of the functional spinal unit (FSU) under the application of moment is important for the biomechanical understanding of physiological and pathological aspects of spine. This paper presents a mechanical model on viscoelastic behavior of intervertebral disc connecting two vertebral bodies where a posterior element and surrounding tissues have been removed from FSU. The model, which is composed of a nonlinear spring and a linear Kelvin element in series, is proposed. Specimen of human lumbar intervertebral disc (L3-intervertebral disc-L4) are used for the experiment of the cyclic moment application of flexion, extension and lateral bending with constant loading rates. Simulations by the proposed model are compared with the experiment. It is suggested that the model is good for the prediction of viscoelastic behavior of the intervertebral disc.

On the Mechanical Behaviour of Intervertebral Discs

The response to compression, shear, bending, and axial rotation of an intervertebral disc is studied by using a theoretical disc model. The annulus fibrosus is modelled by ten fibre layers with alternating fibre inclination. The nucleus pulposus as well as the substance filing the space between the fibre layers is assumed to consist of an incompressible fluid. The end-plates are assumed to bulge at action of the pressure in the fluid phase. Geometry of fibre layers and end-plates are chosen to agree as closely as possible with what is representative for lumbar discs. The results show considerable increase of the different stiffnesses at increasing levels of the axial load. They also show quite large fibre strains, well over 10% at motions within normal physiological limits.

Study in situ et in vivo of the acceleration of lumbar vertebrae of a primate exposed to vibration in the Z-axis

In order to study the propagation of vibration along the spine, the authors developed a method allowing in vivo et in situ measurement of vibrational accelerations in the lower lumbar spine of a primate. The surgical technique used to anchor the miniature accelerometers on the anterior wall of vertebral bodies is described. After recovery, the sitting animal is exposed to a vibration stimulus. Direct recording of data obtained from the lowest four lumbar vertebrae of a healthy live animal provide objective information on the behavior of intervertebral discs and will later permit definition of the role of skeletal muscles in the spinal response to a vibrational stress.

Analysis of load-deflection behavior of intervertebral discs under axial compression using exact parametric solutions of Kelvin-solid models

The analytical modelling of creep response phenomena of intervertebral discs subjected to a constant axial compressive load is attempted by using Kelvin-solid models. A mathematical analysis scheme is proposed for unique model identification wherein exact parameter solutions are developed for the one-Kelvin-unit model, the three-parameter-solid model, and the two-Kelvin-unit model. In addition, a method is presented by which the associated Young's moduli and viscosity coefficients for an identified model are obtainable. Most importantly, unique parameter values are obtained for the three-parameter-solid by utilizing exact model parameter solutions on experimental strain, ε( t), data. This particular model is observed to yield theoretical strain, ε( t) cal, values that are within an average error of 5% of the experimentally measured values, ε( t) exp, for different intervertebral discs. Further, mechanical properties of the intervertebral discs are obtained by using the values of the three-parameter-solid model parameters to calculate the associated Young's moduli and viscosity coefficient. The appropriate applications, data limitations, and possible generalizations of this exact analysis scheme are fully discussed, along with suggestions for future investigatory efforts.