4,497 research outputs found

    Biomechanical evaluation of predictive parameters of progression in adolescent isthmic spondylolisthesis: a computer modeling and simulation study

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    <p>Abstract</p> <p>Background</p> <p>Pelvic incidence, sacral slope and slip percentage have been shown to be important predicting factors for assessing the risk of progression of low- and high-grade spondylolisthesis. Biomechanical factors, which affect the stress distribution and the mechanisms involved in the vertebral slippage, may also influence the risk of progression, but they are still not well known. The objective was to biomechanically evaluate how geometric sacral parameters influence shear and normal stress at the lumbosacral junction in spondylolisthesis.</p> <p>Methods</p> <p>A finite element model of a low-grade L5-S1 spondylolisthesis was constructed, including the morphology of the spine, pelvis and rib cage based on measurements from biplanar radiographs of a patient. Variations provided on this model aimed to study the effects on low grade spondylolisthesis as well as reproduce high grade spondylolisthesis. Normal and shear stresses at the lumbosacral junction were analyzed under various pelvic incidences, sacral slopes and slip percentages. Their influence on progression risk was statistically analyzed using a one-way analysis of variance.</p> <p>Results</p> <p>Stresses were mainly concentrated on the growth plate of S1, on the intervertebral disc of L5-S1, and ahead the sacral dome for low grade spondylolisthesis. For high grade spondylolisthesis, more important compression and shear stresses were seen in the anterior part of the growth plate and disc as compared to the lateral and posterior areas. Stress magnitudes over this area increased with slip percentage, sacral slope and pelvic incidence. Strong correlations were found between pelvic incidence and the resulting compression and shear stresses in the growth plate and intervertebral disc at the L5-S1 junction.</p> <p>Conclusions</p> <p>Progression of the slippage is mostly affected by a movement and an increase of stresses at the lumbosacral junction in accordance with spino-pelvic parameters. The statistical results provide evidence that pelvic incidence is a predictive parameter to determine progression in isthmic spondylolisthesis.</p

    Biomechanical analysis and modeling of different vertebral growth patterns in adolescent idiopathic scoliosis and healthy subjects

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    <p>Abstract</p> <p>Background</p> <p>The etiology of AIS remains unclear, thus various hypotheses concerning its pathomechanism have been proposed. To date, biomechanical modeling has not been used to thoroughly study the influence of the abnormal growth profile (i.e., the growth rate of the vertebral body during the growth period) on the pathomechanism of curve progression in AIS. This study investigated the hypothesis that AIS progression is associated with the abnormal growth profiles of the anterior column of the spine.</p> <p>Methods</p> <p>A finite element model of the spinal column including growth dynamics was utilized. The initial geometric models were constructed from the bi-planar radiographs of a normal subject. Based on this model, five other geometric models were generated to emulate different coronal and sagittal curves. The detailed modeling integrated vertebral body growth plates and growth modulation spinal biomechanics. Ten years of spinal growth was simulated using AIS and normal growth profiles. Sequential measures of spinal alignments were compared.</p> <p>Results</p> <p>(1) Given the initial lateral deformity, the AIS growth profile induced a significant Cobb angle increase, which was roughly between three to five times larger compared to measures utilizing a normal growth profile. (2) Lateral deformities were absent in the models containing no initial coronal curvature. (3) The presence of a smaller kyphosis did not produce an increase lateral deformity on its own. (4) Significant reduction of the kyphosis was found in simulation results of AIS but not when using the growth profile of normal subjects.</p> <p>Conclusion</p> <p>Results from this analysis suggest that accelerated growth profiles may encourage supplementary scoliotic progression and, thus, may pose as a progressive risk factor.</p

    Method to geometrically personalize a detailed finite element model of the spine

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    To date, developing geometrically personalized and detailed solid finite element models of the spine remains a challenge, notably due to multiple articulations and complex geometries. To answer this problem, a methodology based on a free form deformation technique (kriging) was developed to deform a detailed reference finite element mesh of the spine (including discs and ligaments) to the patient-specific geometry of 10 and 82-year old asymptomatic spines. Different kriging configurations were tested: with or without smoothing, and control points on or surrounding the entire mesh. Based on the results, it is recommended to use surrounding control points and smoothing. The mean node to surface distance between the deformed and target geometries was 0.3 mm ± 1.1. Most elements met the mesh quality criteria (95%) after deformation, without interference at the articular facets. The method’s novelty lies in the deformation of the entire spine at once, as opposed to deforming each vertebra separately, with surrounding control points and smoothing. This enables the transformation of reference vertebrae and soft tissues to obtain complete and personalized FEMs of the spine with minimal post-processing to optimize the mesh. Biomechanics

    Development Of A Finite Element Pelvis And Lower Extremity Model With Growth Plates For Pediatric Pedestrian Protection

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    Finite element (FE) model is a useful tool frequently used for investigating the injury mechanisms and designing protection countermeasures. At present, no 10 years old (YO) pedestrian FE model has been developed from appropriate anthropometries and validated against limitedly available impact response data. A 10 YO child FE pelvis and lower extremities (PLEX) model was established to fill the gap of lacking such models in this age group. The baseline model was validated against available pediatric postmortem human subjects (PMHS) test data and additional scaled adult data, then the PLEX model was integrated to build a whole-body FE model representing a 10 YO pedestrian. Additional investigations revealed that the immature tissues, growth plates (GPs), should be explicitly modeled because they have different mechanical properties than the surrounding bones. Epidemiological data revealed that GP accounted for a large portion of pediatric fractures. To investigate the GP’s material property for further advancement of the baseline PLEX FE model for simulating impact mechanical responses, a series of tensile and shearing experiments on porcine bone-GP-bone units were carried out. The GPs from the femoral head, distal femur, and proximal tibia of 20-weeks-old piglets were tested, under different strain rates. Randomized block ANOVA was conducted to determine the effects of anatomic region and strain rate on the material properties of GPs. By comparing the porcine experimental data to the limited data obtained from tests on human subjects reported in the literature, an optimal conversion factor was derived to correlate the material properties of 20-week-old piglet GPs and 10 YO child GPs. A transversely isotropic hyperelastic material model (MAT_92 available in LS-DYNA) with added viscosity was adopted to mimic the GP tissues. After a series of optimization procedures, the material parameter sets needed for MAT_92 were determined to represent the GPs of a 10 YO child. To further explore the GP modeling techniques, a sub-model representing the proximal femur was extracted from the PLEX model. The femoral head GP in the sub-model was modeled using the geometry from CT scans and the material properties from early optimizations. FE simulations of femoral head shearing were conducted on the sub-model to determine other GP modeling settings. In the following technical application, similar GP modeling techniques were implemented to model the GPs at the hip and knee regions to update the baseline PLEX model, and further the whole-body model. An SUV-to-pedestrian impact scenario was simulated using the updated whole-body model, the remarkable influences of the GPs on the stress distributions in the PLEX were quantitatively assessed

    Computational modelling of the scoliotic spine: A literature review

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    Scoliosis is a deformity of the spine that in severe cases requires surgical treatment. There is still disagreement among clinicians as to what the aim of such treatment is as well as the optimal surgical technique. Numerical models can aid clinical decision-making by estimating the outcome of a given surgical intervention. This paper provided some background information on the modelling of the healthy spine and a review of the literature on scoliotic spine models, their validation, and their application. An overview of the methods and techniques used to construct scoliotic finite element and multibody models was given as well as the boundary conditions used in the simulations. The current limitations of the models were discussed as well as how such limitations are addressed in non-scoliotic spine models. Finally, future directions for the numerical modelling of scoliosis were addressed

    Computational modelling of the scoliotic spine: A literature review

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    open4siScoliosis is a deformity of the spine that in severe cases requires surgical treatment. There is still disagreement among clinicians as to what the aim of such treatment is as well as the optimal surgical technique. Numerical models can aid clinical decision-making by estimating the outcome of a given surgical intervention. This paper provided some background information on the modelling of the healthy spine and a review of the literature on scoliotic spine models, their validation, and their application. An overview of the methods and techniques used to construct scoliotic finite element and multibody models was given as well as the boundary conditions used in the simulations. The current limitations of the models were discussed as well as how such limitations are addressed in non-scoliotic spine models. Finally, future directions for the numerical modelling of scoliosis were addressed.Marco Viceconti and Giorgio Davico were supported by the EU funded project Mobilise-D. The charity Reuse-WithLove is gratefully acknowledged for the financial support to this research.openGould, Samuele L; Cristofolini, Luca; Davico, Giorgio; Viceconti, MarcoGould, Samuele L; Cristofolini, Luca; Davico, Giorgio; Viceconti, Marc

    Utilization of Finite Element Analysis Techniques for Adolescent Idiopathic Scoliosis Surgical Planning

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    Adolescent Idiopathic Scoliosis, a three-dimensional deformity of the thoracolumbar spine, affects approximately 1-3% of patients ages 10-18. Surgical correction and treatment of the spinal column is a costly and high-risk task that is consistently complicated by factors such as patient-specific spinal deformities, curve flexibility, and surgeon experience. The following dissertation utilizes finite element analysis to develop a cost-effective, building-block approach by which surgical procedures and kinematic evaluations may be investigated. All studies conducted are based off a volumetric, thoracolumbar finite element (FE) model developed from computer-aided design (CAD) anatomy whose components are kinematically validated with in-vitro data. Spinal ligament stiffness properties derived from the literature are compared for kinematic assessment of a thoracic functional spinal unit (FSU) and benchmarked with available in-vitro kinematic data. Once ligament stiffness properties were selected, load sharing among soft tissues (e.g., ligaments and intervertebral disc) within the same FSU is then assessed during individual steps of a posterior correction procedure commonly used on scoliosis patients. Finally, the entire thoracolumbar spine is utilized to mechanically induce a mild scoliosis profile through an iterative preload and growth procedure described by the Hueter-Volkmann law. The mild scoliosis model is then kinematically compared with an asymptomatic counterpart. The thoracic deformation exhibited in the mild scoliosis model compared well with available CT datasets. Key findings of the studies confirm the importance of appropriately assigning spinal ligament properties with traditional toe and linear stiffness regimes to properly characterize thoracic spine FE models. Stiffness properties assigned within spinal FE models may also alter how intact ligaments and intervertebral discs respond to external loads during posterior correction procedures involving serial ligament removal, and thus can affect any desired post-surgical outcomes. Lastly, the thoracolumbar spine containing mild scoliosis experiences up to a 37% reduction in global range of motion compared to an asymptomatic spine, while also exhibiting larger decreases in segmental axial rotations at apical deformity levels. Future studies will address kinematic behavior of a severe scoliosis deformity and set the stage for column-based osseoligamentous load sharing assessments during surgical procedures

    Modeling and analysis of proximal tibial growth plate fractures in adolescents

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    Today, children and adolescents are participating heavily in organized athletics year-round. Each year, approximately one third of these children will experience a serious injury requiring a doctor\u27s or hospital visit. A large number of these are overuse injuries. Physeal, or growth plate fractures, are one such type of overuse injury commonly seen in adolescents. At the knee joint, overuse injuries in adolescents occur most often in the proximal region of the tibia. Conversely, in mature adults, overuse injuries manifest themselves more often at the middle/distal third junction of the tibia, or in the soft tissues of the knee joint. While the exact reasons for this difference have not been directly and definitively quantified, several hypotheses have been suggested. They include differences in mechanical movement strategies, changes in limb inertial and material properties, and the timing of these changes in relation to one another.In addition, the presence of an inherently weaker growth plate is present throughout growth, since the growth plate is the last portion of the bone to ossify. This renders the epiphyseal and metaphyseal; areas more susceptible to injury than the than the diaphysis, and loads that would typically cause damage or rupture to soft tissues like the ACL or MCL instead disrupt the weaker physeal plate. This thesis aims to compare the changes in and interaction of inertial properties and forces produced by the quadriceps via the patellar tendon and tibiofemoral contact before and after puberty. To this end, these forces were first determined using Kane\u27s method of dynamics in conjunction with an isometric knee extension study yielding separate adult and youth data. These results were then utilized in the finite element software package Abaqus to load tibial models with varying material properties and investigate changes in stress and strain at the proximal tibia.Shortened patellar ligament and increased force at the ankle had the greatest effect on forces at the proximal tibia. The areas at greatest risk for fracture from the finite element analysis were the posterior and lateral/medial portions of the metaphysis

    Biomechanical analysis and modeling of lumbar belt: Preliminary study.

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    International audienceLow back pain is a major public health problem in European Countries. In France, about 50% of population is suffering of this pathology every year (Fassier 2011). Because of health care cost and sick leave (Fassier 2011; Leclerc et al. 2009), low back pain has both societal and economic adverse consequences. Many treatments are proposed. However no guideline is provided to physician. Treatment depends on patient, on low back pain type and evolution and also on physician knowledge and believes. Medical devices, as lumbar belt might be proposed to treat low back pain. Several clinical trials have shown their efficacy (Calmels et al. 2009). Nevertheless, both mechanical and physiological effects of lumbar belts remain unclear. In this study, the application of a lumbar belt on the trunk is simulated by a finite element model. It is often assumed that the pain comes from the toe of the intervertebral discs and is related only to the intradiscal pressure and the thoracolumbar posture. Beside, abdominal pressure is used by belt manufacturers as a marker of the lumbar belt efficiency, because a change in the abdominal pressure could bring a change in the thoracolumbar posture and consequently on the intradiscal pressure. That's why the goal of this study is to determine the mechanical effect of wearing lumbar belt: i) on abdominal pressure; ii) on thoracolumbar posture; iii) on intervertebral disc pressure
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