Poroelastic Finite Element Model Research Articles

Revealing Detailed Cartilage Function Through Nanoparticle Diffusion Imaging: A Computed Tomography & Finite Element Study

The ability of articular cartilage to withstand significant mechanical stresses during activities, such as walking or running, relies on its distinctive structure. Integrating detailed tissue properties into subject-specific biomechanical models is challenging due to the complexity of analyzing these characteristics. This limitation compromises the accuracy of models in replicating cartilage function and impacts predictive capabilities. To address this, methods revealing cartilage function at the constituent-specific level are essential. In this study, we demonstrated that computational modeling derived individual constituent-specific biomechanical properties could be predicted by a novel nanoparticle contrast-enhanced computer tomography (CECT) method. We imaged articular cartilage samples collected from the equine stifle joint (n = 60) using contrast-enhanced micro-computed tomography (µCECT) to determine contrast agents’ intake within the samples, and compared those to cartilage functional properties, derived from a fibril-reinforced poroelastic finite element model. Two distinct imaging techniques were investigated: conventional energy-integrating µCECT employing a cationic tantalum oxide nanoparticle (Ta2O5-cNP) contrast agent and novel photon-counting µCECT utilizing a dual-contrast agent, comprising Ta2O5-cNP and neutral iodixanol. The results demonstrate the capacity to evaluate fibrillar and non-fibrillar functionality of cartilage, along with permeability-affected fluid flow in cartilage. This finding indicates the feasibility of incorporating these specific functional properties into biomechanical computational models, holding potential for personalized approaches to cartilage diagnostics and treatment.

A mechano-regulation model to design and optimize the surface microgeometry of titanium textured devices for biomedical applications

In a technological context where, thanks to the additive manufacturing techniques, even sophisticated geometries as well as surfaces with specific micrometric features can be realized, we propose a mechano-regulation algorithm to determine the optimal microgeometric parameters of the surface of textured titanium devices for biomedical applications. A poroelastic finite element model was developed including a portion of bone, a portion of a textured titanium device and a layer of granulation tissue separating the bone from the device and occupying the space between them. The algorithm, implemented in the Matlab environment, determines the optimal values of the root mean square and the correlation length that the device surface must possess to maximize bone formation in the gap between the bone and the device. For low levels of compression load acting on the bone, the algorithm predicts low values of root mean square and high values of correlation length. Conversely, high levels of load require high values of root mean square and low values of correlation length. The optimal microgeometrical parameters were determined for various thickness values of the granulation tissue layer. Interestingly, the predictions of the proposed computational model are consistent with the experimental results reported in the literature. The proposed algorithm shows promise as a valuable tool for addressing the demands of precision medicine. In this approach, the device or prosthesis is no longer designed solely based on statistical averages but is tailored to each patient's unique anthropometric characteristics, as well as considerations related to their metabolism, sex, age, and more.

Bayesian Monte Carlo Inversion of InSAR Time Series Deformation Induced by Wastewater Injection: A Case Study in West Texas

AbstractWastewater disposal can induce detectable surface uplift, which may cause ground instability and threaten infrastructure. The distributions of local hydro‐geomechanical parameters, especially Young's modulus and hydraulic conductivity, play an essential role in these geohazards. To constrain these parameters, we have inverted spatio‐temporal deformation measured by Interferometric Synthetic Aperture Radar (InSAR) and injection information using a Bayesian Monte Carlo approach with a poroelastic finite element model. Sentinel‐1A/B imagery from 2014 to 2020 is processed to track the spatio‐temporal deformation in Winkler county, West Texas, USA. The posterior distribution of subsurface effective volumes reveals under‐reported volumes in the well near the deformation center. In addition, the inversion results provide better constraints for the parameters than those solely obtained based on the cumulative spatial deformation or temporal development of the deformation center.

Anatomical parameters alter the biomechanical responses of adjacent segments following lumbar fusion surgery: Personalized poroelastic finite element modelling investigations.

Introduction: While the short-term post-operative outcome of lumbar fusion is satisfying for most patients, adjacent segment disease (ASD) can be prevalent in long-term clinical observations. It might be valuable to investigate if inherent geometrical differences among patients can significantly alter the biomechanics of adjacent levels post-surgery. This study aimed to utilize a validated geometrically personalized poroelastic finite element (FE) modeling technique to evaluate the alteration of biomechanical response in adjacent segments post-fusion. Methods: Thirty patients were categorized for evaluation in this study into two distinct groups [i.e., 1) non-ASD and 2) ASD patients] based on other long-term clinical follow-up investigations. To evaluate the time-dependent responses of the models subjected to cyclic loading, a daily cyclic loading scenario was applied to the FE models. Different rotational movements in different planes were superimposed using a 10Nm moment after daily loading to compare the rotational motions with those at the beginning of cyclic loading. The biomechanical responses of the lumbosacral FE spine models in both groups were analyzed and compared before and after daily loading. Results: The achieved comparative errors between the FE results and clinical images were on average below 20% and 25% for pre-op and post-op models, respectively, which confirms the applicability of this predictive algorithm for rough pre-planning estimations. The results showed that the disc height loss and fluid loss were increased for the adjacent discs in post-op models after 16h of cyclic loading. In addition, significant differences in disc height loss and fluid loss were observed between the patients who were in the non-ASD and ASD groups. Similarly, the increased stress and fiber strain in the annulus fibrosus (AF) was higher in the adjacent level of post-op models. However, the calculated stress and fiber strain values were significantly higher for patients with ASD. Discussion: Evaluating the biomechanical response of pre-op and post-op modeling in the non-ASD and ASD groups showed that the inherent geometric differences among patients cause significant variations in the estimated mechanical response. In conclusion, the results of the current study highlighted the effect of geometrical parameters (which may refer to the anatomical conditions or the induced modifications regarding surgical techniques) on time-dependent responses of lumbar spine biomechanics.

Comparative biomechanical analyses of lower cervical spine post anterior fusion versus intervertebral disc arthroplasty: A geometrically patient-specific poroelastic finite element investigation.

Background/ObjectiveThe optimal surgical technique for the treatment of cervical degenerative disc disease (CDDD) towards decreasing the risk of adjacent segment disease (ASD) remains elusive. This study aimed to comparatively investigate the biomechanics of the lower cervical spine following fusion (ACDF) and artificial disc arthroplasty (Bryan® and Prestige LP®) using a validated geometrically patient-specific poroelastic finite element modeling (FEM) approach.MethodsTen subject-specific pre-operative models were developed and validated based on a FEM approach. Poroelastic models were then constructed using post-operation images for three different treatment scenarios: ACDF; Prestige LP® and Bryan® artificial discs at the C5–C6 level. The biomechanical responses at both surgical and adjacent spinal levels were studied subject to static and cyclic loading.ResultsPostoperatively, greater range of motion (ROM), higher annulus fibrosus stress and strain values, and increased disc height and fluid loss at the adjacent levels were detected post ACDF, as compared with pre-op as well as artificial disc arthroplasty. The facet joint forces were larger for the Prestige LP® disc, particularly during extension. The lowest values in disc height and fluid exchange were observed in the Bryan® artificial disc arthroplasty models.ConclusionBiomechanical analyses revealed that ACDF poses the highest potential risk for adjacent disc degeneration. The artificial discs investigated here (Prestige LP® and Bryan®) not only preserved motion at the instrumented level, but also sustained the pre-op ROM and decreased the intradiscal pressure (IDP) and facet joint forces (FJFs) at adjacent levels, particularly during flexion/extension. The Bryan® artificial disc demonstrated the most efficacy in maintaining the natural poroelastic characteristics of adjacent discs.The translational potential of this articleThis study provided a technique for clinicians to use quantitative data towards subject-specific evaluation to comparatively evaluate the impact of ACDF and disc arthroplasty using two types of artificial discs on the biomechanics of the cervical spine. It confirms differences in the poroelastic characteristics of adjacent discs for different fixation techniques, and reveals the advantage of artificial discs with a flexible core for decreasing the risk of ASD.

Effects of Osteocyte Shape on Fluid Flow and Fluid Shear Stress of the Loaded Bone.

This study was conducted to better understand the specific behavior of the intraosseous fluid flow. We calculated the number and distribution of bone canaliculi around the osteocytes based on the varying shapes of osteocytes. We then used these calculated parameters and other bone microstructure data to estimate the anisotropy permeability of the lacunar-canalicular network. Poroelastic finite element models of the osteon were established, and the influence of the osteocyte shape on the fluid flow properties of osteons under an axial displacement load was analyzed. Two types of boundary conditions (BC) that might occur in physiological environments were considered on the cement line of the osteon. BC1 allows free fluid passage from the outer elastic restraint boundary, and BC2 is impermeable and allows no free fluid passage from outer displacement constrained boundary. They both have the same inner boundary conditions that allow fluid to pass through. Changes in the osteocyte shape altered the maximum value of pressure gradient (PG), pore pressure (PP), fluid velocity (FV), and fluid shear stress (FSS) relative to the reference model (spherical osteocytes). The maximum PG, PP, FV, and FSS in BC2 were nearly 100% larger than those in BC1, respectively. It is found that the BC1 was closer to the real physiological environment. The fluid flow along different directions in the elongated osteocyte model was more evident than that in other models, which may have been due to the large difference in permeability along different directions. Changes in osteocyte shape significantly affect the degrees of anisotropy of fluid flow and porous media of the osteon. The model presented in this study can accurately quantify fluid flow in the lacunar-canalicular network.

Interactive effects of various loading parameters on the fluid dynamics within the lacunar-canalicular system for a single osteocyte.

The osteocyte lacunar-canalicular system (LCS) serves as a mechanotransductive core where external loading applied to the skeleton is transduced into mechanical signals (e.g., fluid shear) that can be sensed by mechanosensors (osteocytes). The fluid velocity and shear stress within the LCS are affected by various loading parameters. However, the interactive effect of distinct loading parameters on the velocity and shear stress in the LCS remains unclear. To address this issue, we developed a multiscale modeling approach, combining a poroelastic finite element (FE) model with a single osteocytic LCS unit model to calculate the flow velocity and shear stress within the LCS. Next, a sensitivity analysis was performed to investigate individual and interactive effects of strain magnitude, strain rate, number of cycles, and intervening short rests between loading cycles on the velocity and shear stress around the osteocyte. Lastly, we developed a relatively simple regression model to predict those outcomes. Our results demonstrated that the strain magnitude or rate alone were the main factors affecting the velocity and shear stress; however, the combination of these two was not directly additive, and addition of a short rest between cycles could enhance the combination of these two related factors. These results show highly interactive effects of distinct loading parameters on fluid velocity and shear stress in the LCS. Specifically, our results suggest that an enhanced fluid dynamics environment in the LCS can be achieved with a brief number of load cycles combined with short rest insertion and high strain magnitude and rate.

Comparative biomechanical analysis of rigid vs. flexible fixation devices for the lumbar spine: A geometrically patient-specific poroelastic finite element study

Background and ObjectiveLumbar spinal stenosis (LSS), or the narrowing of the spinal canal, continues to be the leading preoperative diagnosis for adults older than 65 years who undergo spine surgery. Although the treatment of LSS depends on its severity, the optimal surgical technique towards decreasing the risk of adjacent segment disease (ASD) remains elusive. This study aimed to comparatively analyze spinal biomechanics with rigid and flexible fixation devices (i.e., rigid and dynamic posterolateral fusion (PLF) and interspinous process (ISP) devices) during daily activities. MethodsUsing a validated parametric poroelastic finite element modeling approach, 8 subject-specific pre-operative models were developed, and their validity was evaluated. Parametric FE models of the lumbar spines were then regenerated based on post-operation images for (A) rigid PLF (B) dynamic PLF (C) rigid ISP device (Coflex) and (D) flexible ISP device (DIAM) at L4-L5 level. Biomechanical responses for instrumented and adjacent intervertebral discs (IVDs) were analyzed and compared subject to static and cyclic loading. ResultsThe preoperative models were well comparable with previous works in literature. The postoperative results for the PLF and Coflex rigid systems, demonstrated greater ROM; higher values of stress and strain in the AF region; and increased disc height and fluid loss at the adjacent levels, as compared with the pre-op models and the post-op results of the flexible systems (i.e., dynamic PLF and DIAM). The calculated forces on the facet joint were of smaller magnitude for the ISP devices as compared to the PLF, particularly during extension. ConclusionsThis study demonstrates that the dynamic PLF construct and DIAM implants could be effective to maintain the natural poroelastic characteristics of adjacent IVDs, which could be beneficial for enhancing long-term clinical outcomes. FEM provides clinicians with an invaluable patient-specific quantitative tool for informed surgical planning and discerning follow-up management.

Prediction of the natural frequencies of different degrees of degenerated human lumbar segments L2-L3 using dynamic finite element analysis

Background and ObjectiveChronic exposure to resonant environment may cause more serious injuries to human lumbar spine than other vibrations. On the condition that the natural frequency of human lumbar spine is known, excitation frequency from an external vibration source can be optimized to keep away from the natural frequency and thus avoid lumbar resonance. Therefore, this study aimed to present an approach to predict the natural frequency of the human lumbar spine. MethodsFour poroelastic finite element models of human L2–L3 spinal motion segments with different degrees of degeneration were established. Dynamic finite element analyses of these models during 1 h of vibration were then conducted. The mechanical parameters of these models under vibrations at different excitation frequencies were predicted. The excitation frequencies that resulted in the greatest changes in the lumbar mechanical parameters were identified as the natural frequencies of the established L2–L3 spinal motion segments. ResultsSimulation results showed that the natural frequencies of the healthy and mildly degenerated L2–L3 spinal motion segments, moderately degenerated L2–L3 spinal motion segments, and seriously degenerated L2–L3 spinal motion segments were in the range of 5–7, 3–5, and 1–3 Hz, respectively. ConclusionsThe predicted results indicated that the natural frequencies of the human L2–L3 spinal motion segments gradually decreased with the severity of degeneration. These phenomena may be related to changes in the lumbar structures and materials because of degeneration. This study provided a feasible method to predict the lumbar natural frequencies for different populations, which may be helpful in optimizing external vibration sources to avoid lumbar resonance.

Numerical study of long-time growth of hydraulic fractures in a line drive

This work concerns detailed numerical modelling of injection fracturing in chalk formations under 2–3 km burial. The conditions and properties are chosen to resemble field conditions as typically found in oil fields subject to water injection in the Central Graben in the North Sea off-shore Denmark, Norway and the UK, but the studied phenomena are general to injection fracturing irrespective of geographical location and technological application. The complexity of reality is a challenging factor when mathematical models of hydraulic fractures in the subsurface are formulated. To this end the finite element method and a multi physics approach is instrumental, and data from fields developed and operated under conditions prudent for modelling are equally important. In the present study, a poroelastic finite element model is applied and used under plane strain conditions for a linear fracture mechanics investigation. This approach is suitable for analysing fracturing in arrays of parallel and horizontal wells as can be found in many oil fields undergoing water-flooding. Based on realistic field data, e.g. reservoir properties and rate and pressure scenarios representative for typical fields in the North Sea region, fracture initiation and fracture growth are analysed in details in a realistic field setting. Using a formulation of the J-integral, that includes Functionally Graded Material and poroelastic effects, it is demonstrated that formation fracture toughness determines fracture initiation and fracture height. The fracture propagation speed is controlled by continuity, e.g. the injection rate must balance the leak-off from the fracture wall. By combining the fields of geotechnical engineering, petroleum engineering and mechanical engineering with realistic data measurements, this study provides a novel realistic study of how the producer and injector pressure influence the fracturing process for induced hydraulic fractures in a line drive.

Investigation of fluid flow velocity within the intervertebral disc

Enhancing fluid flow velocity within the intervertebral disc may allow to increase solute transportation rates and improve disc nutrition as the sufficient supply of the nutrients to cells of intervertebral disc is a key factor in order to avoid or delay processes of disc degeneration. Poroelastic finite element model of lumbar intervertebral disc is used to calculate fluid flow velocity with the intervertebral disc due to flexion, extension, lateral bending and axial rotation. When comparing the average of flow velocity, the highest values are calculated when flexion and extension moments were applied to the disc, but lateral bending induces the highest value of velocity component in Y direction in nucleus pulposus, yet the assumption that lateral bending could be more beneficial in order to improve nutrients supply to intervertebral disc cannot be substantiated only by this data, as calculated values of velocity component Y are significantly lower that total velocity values.

Finite element investigation on the dynamic mechanical properties of low-frequency vibrations on human L2-L3 spinal motion segments with different degrees of degeneration.

Exposure to low-frequency vibration is harmful to human lumbar health. However, the dynamic mechanical properties of lumbar spines with varying degrees of degeneration during time-dependent vibration remain incompletely understood. In this study, four poroelastic finite element models of human L2-L3 spinal motion segments, including the non-degeneration and the mild, moderate, and serious degeneration, were established. One-hour low-frequency vibrations with different frequencies were applied. Then, the dynamic mechanical properties of different degenerated lumbar models under the same vibration and the same lumbar model under vibrations at different frequencies were investigated. The results indicated and implied that the negative influences of 1-h vibration on the dynamic mechanical properties of the non-degenerated and mildly degenerated models were similar, but became obvious for the moderately and seriously degenerated models with time. Therefore, the damage caused by low-frequency vibration on the degenerated spinal motion segments was more serious compared with that on the healthy one. Meanwhile, the dynamic mechanical properties of the same lumbar model under vibrations at different frequencies expressed the negligible differences when the vibration frequency was not close to the lumbar natural frequency. Thus, the effects of the 1-h vibrations at different frequencies on one spinal motion segment were similar. Vibration frequency sensitivity analysis on the dynamic characteristics of human L2-L3 spinal motion segments with different degrees of degeneration.

Understanding Vectorial Migration Patterns of Wastewater-Induced Earthquakes in the United States

ABSTRACTThe recent surge of earthquakes in the central United States is linked to the disposal of large volumes of wastewater. Even if injection rates have been decreasing since 2015, the seismic hazard remains elevated. Moreover, some events in Kansas occur far from disposal wells. We applied a multidimensional cross-correlation technique to analyze the spatiotemporal relation between fluid injection and earthquakes. While a strong correlation is observed in east-northeastern direction of the disposal wells for the majority of events, some earthquakes occur in northeastern direction far from the disposal wells. We explain this pattern and the large-scale evolution of borehole pressure observations by directional migration of poroelastic stresses and pore pressure diffusion. This follows from our principal 2D poroelastic finite-element model that has a predicting power and identifies controlling parameters of the process. These are the permeability of the basement and its anisotropic character as well as the distribution of critical fault strengths. Our results suggest that remote locations may be destabilized even when injection rates are declining. Thus, a volume reduction may only provide an immediate effect to lower the seismicity locally. It follows that a state-wide reduction in earthquakes may require longer waiting times and that the hazard of induced seismicity may remain elevated for tens of years.

Multi-scale mechanotransduction of the poroelastic signals from osteon to osteocyte in bone tissue

In order to quantify the poroelastic mechanical signals conduction and evaluate the biomechanical effectiveness of functional units (osteocyte processes, canaliculi and lacuna) in lacunar-canalicular system (LCS), a multiscale poroelastic finite element model was established by using the Comsol Multiphysics software. The poroelastic mechanical signals (pore pressure, fluid velocity, von-Mises stress, strain) were analyzed inside the osteon-osteocyte system. The effects of osteocyte (OCY)’s shape (ellipse and circle), long axis directions (horizontal and vertical) and mechanical properties (Elastic modulus and permeability) on its poroelastic responses were examined. It is found that the OCY processes is the best mechanosensor compared with the OCY body, lacunae and canaliculi. The mechanotransduction ability of the elliptic shaped OCY is stronger than that of circular shaped. The pore pressure and flow velocity around OCYs increase as the elastic modulus and permeability of OCY increase. The established model can be used for studying the mechanism of bone mechanotransduction at the multiscale level.

The response surface method-genetic algorithm for identification of the lumbar intervertebral disc material parameters

Long-term compressive load on the lumbar intervertebral disc (IVD) might lead to lumbar IVD herniation. Exploring the material parameters of normal and degenerative enucleated IVDs is the basis for studying their mechanical behavior. According to the inverse analysis principle of the parameter estimation, an optimization method was proposed to identify the parameters of the porous material of the lumbar IVD based on finite element inverse analysis. The poroelastic finite element models were established in line with the compression creep experiment. The material parameters were combined by Box–Behnken design (BBD), and the response surface (RS) models were constructed using a quadratic polynomial with cross terms and optimized by genetic algorithm (GA). The results showed that the simulation result of the best material parameter combination had a good agreement with the experiment. Compared with the normal lumbar IVD, the elastic modulus and permeability decreased, and Poisson's ratio increased for the enucleated disk, resulting in a significant difference in mechanical properties. The algorithm used in this study can reduce the parameter identification error compared with only the RS method, and decrease the number of finite element simulations compared with only the GA.

Near-salt perturbations of stresses and pore fluid pressures and their impacts on wellbore stability in the Kuqa depression of the Tarim Basin, China

Salt structures are highly associated with economic hydrocarbon reservoirs. However, drilling a wellbore near or through the salt is usually difficult because the near-salt stresses and pore fluid pressures are largely perturbed due to weaker mechanical strength of salt bodies than their surrounding sediments. We have developed a 2D plane-strain poroelastic finite-element model to simulate stresses and pore pressures in the horizontal-compression salt tectonic system, the Kuqa depression in the Tarim Basin, China, and we use the model results of stresses and pore pressures to calculate safe drilling mud weights on drilling in the salt basin. We found that in early stage of the transient process (close to the undrained condition), pore fluid overpressure occurs at salt convex due to additional compression, whereas underpressure occurs at salt concave due to additional extension within the minibasin. Horizontal effective stress decreases at salt concave (within the minibasin) but increases at salt convex; vertical effective stress varies oppositely to horizontal effective stress. In the final stage of the transient process (drained condition), overpressure has dissipated and pore pressure remains hydrostatic, and stress perturbations are similar to those from the static geomechanical model with elastic sediments: horizontal stress increases at salt convex but decreases at salt concave; vertical stress slightly increases at salt convex and concave. Our calculated safe drilling mud weights and their windows vary over time. Especially at the salt convex, the safe windows are relatively narrow in the early stage of the transient process but become wider in later stage because overpressure dissipates over time and this makes drilling easier. Our results indicate different perturbation patterns of stresses and pore pressures near different salt geometries in a horizontal-compression salt tectonic system, and provide insights into wellbore drilling design and safe drilling mud weights in the salt system.

Wastewater leakage in West Texas revealed by satellite radar imagery and numerical modeling

Wastewater, a byproduct of oil and gas production, is injected into disposal wells. Using Interferometric Synthetic Aperture Radar (InSAR) to observe ground deformation in the Ken Regan field, West Texas, we detected surface uplift that occurred near a wastewater disposal well from 2007 to 2011. High correlation between the observed deformation and the injection volume suggests that the uplift was caused by wastewater disposal in the well. Inverse elastic models were first used to calculate the injection depth and volume. Given the initial estimates of wastewater injection, forward poroelastic finite element models were applied to simulate stress/strain and displacement fields and to estimate the effective injection volume and depth, so as to ultimately understand the subsurface geomechanical processes and provide insight into the local hydrologic properties of the strata in the well location. Results from both elastic and poroelastic models indicate that the effective injection depth is much shallower than the depth reported to the Texas Railroad Commission (RRC). The most reasonable explanation is that the well was experiencing leakage due to casing failures and/or sealing problem(s). The Rustler Aquifer, within the zone of the effective injection depth, has been used as a source of freshwater for irrigation and livestock; wastewater leaked into this aquifer may possibly contaminate that freshwater. Our analysis that exploits remote sensing data and numerical models provides a clue as to understanding the subsurface hydrogeological process responding to the oil and gas activities and an indirect leakage monitoring method to supplement current infrequent leakage detection.

Biomechanical Evaluation of the Effect of Mesenchymal Stem Cells on Cartilage Regeneration in Knee Joint Osteoarthritis

Numerous clinical studies have reported cell-based treatments for cartilage regeneration in knee joint osteoarthritis using mesenchymal stem cells (MSCs). However, the post-surgery rehabilitation and weight-bearing times remain unclear. Phenomenological computational models of cartilage regeneration have been only partially successful in predicting experimental results and this may be due to simplistic modeling assumptions and loading conditions of cellular activity. In the present study, we developed a knee joint model of cell and tissue differentiation based on a more mechanistic approach, which was applied to cartilage regeneration in osteoarthritis. First, a phenomenological biphasic poroelastic finite element model was developed and validated according to a previous study. Second, this method was applied to a real knee joint model with a cartilage defect created to simulate the tissue regeneration process. The knee joint model was able to accurately predict several aspects of cartilage regeneration, such as the cell and tissue distributions in the cartilage defect. Additionally, our results indicated that gait cycle loading with flexion was helpful for cartilage regeneration compared to the use of simple weight-bearing loading.

Influence of vibration frequency variation on poroelastic response of intervertebral disc of lumbar spine

Long-time working under whole body vibration might accelerate the degeneration of spine and lead to low back pain and other spinal diseases. A poroelastic finite element model of L4-L5 disc segment was generated to investigate the biomechanical response of lumbar spine under different frequency vibration loads. The results show that the change of the deformation, pore pressure, stress and fluid flow under 8 Hz and 11.5 Hz vibration loads appears periodic; however, the change under lower frequency vibration loads (1 Hz and 4 Hz) is relatively gentle. With increasing time, the axial displacement of disc increases, the liquid gradually flows away and the pore pressure and effective stress in nucleus all show an upward trend. The deformation, stress and fluid flow of the L4-L5 disc segment present a periodicity under higher-frequency vibration loads; however, the fluctuation period is larger than the load frequency, which means that the poroelastic characteristic of intervertebral disc presents a strong damping effect. The effective stress and pore pressure of the nucleus show a rising trend under vibration loads. The findings of this study exhibited the poroelastic performance of the spine under different frequency vibration loads.

Effects of Daily Mastication on Bone Remodeling With Implant-Tooth-Supported Fixed Partial Prosthesis: A Finite Element Study

Implant-tooth-supported fixed dentures are designed clinically due to the limitation of the local anatomy in specific implant sites or following an implant failure. However, it is difficult to precisely simulate the post-surgical biomechanical behavior on alveolar bone tissue with daily mastication. This paper presents and validates a reliable system to predict alveolar bone material properties and to identify the best fit treatment. We randomly chose 23 patients who had been followed for at least three years after Implant-tooth-supported fixed dentures. A poroelastic finite element model (FEM) is designed to characterize the biomechanical stresses of the aortic tissue for each patient. The Kernel least mean square is used to model the relationship between the alveolar bone material properties and biomechanical stress features generated by the daily occlusal force. Therefore, the alveolar bone material properties and the optimal treatment can be predicted by this integrated model prior to the operation for a new patient. The prediction accuracy of our model is 91.5%, more accurate than linear finite element model-LFEM (72.8%), mass-spring model-MSM (78.5%), and mass tensor model-MTM (80.2%). That demonstrates the high value of this model as a decision-making assistant for surgical planning of the patients who are scheduled to undergo dentures. The results of this paper demonstrate that this integrated model can predict alveolar bone material properties postoperatively with high accuracy. It combines bio-mechanical and machine learning approach to create a surgical planning tool which may support the clinical decision in the future.