Establishment Of A 3-D Nonlinear Finite Element Model Of Thoraco-lumbar Vertebral Compression Fractures And Biomechanical Analysis About The Treatment By Hyperextending

Objective: To construct and validate the effectiveness of the 3-D nonlinear finite element models of thoracolumbar and thoracolumbar vertebral compression fractures and investigate the biomechanical mechanism of the treatment about thoracolumbar vertebral compression fractures by hyperextending.Methods: Reconstructed the 3-dimensional bone-geometry of T₁₁-L₂ based on the ultrathin CT scan datas of a young male volunteer.After automatic element meshing, we defined material property of bones by CT value based grading method. We constructedthe volumeof 3 discs and performed refined meshing by hand. The every part of the disc carry out boolean operating.All ligament-elements were constructed according to their anatomic research datas, whose material property were defined by their forcedisplacement curve that modeled with 6 point staged linear method. The elements of cartilages and contact pairs were constructed on the joint surfaces of the zygapophysial joints to simulate contact behavior of joints. After the 3-D nonlinear finite element model of thoracolumbar was constructed, this model was applied static moment load that equals to cadaver mechanic experiment, to simulate various movements of thoracolumbar and validate the effectiveness of this model. After validation of this finite element model of thoracolumbar to establish the 3-D nonlinear finite element models of the compression fractures of T₁₂ and T₁₂L₁ by imposing displacement and simulating the injury mechanism of thoracolumbar vertebral compression fractures. Then establish the 3-D nonlinear finite element models of the compression fractures of T₁₂ based on the ultrathin CT scan datas of one patient of the compression fractures of T₁₂. Validated the effectiveness of the two models by applying static moment loads. Simulate the clinical reduction approach of hyperextension at the different fulcrum of the 3-D nonlinear finite element models of the compression fractures of T₁₂ based on the original datas from the normal human. Analysing the changes of stress and displacement about the different parts of the injured vertebra in the entire reduction.Results: This 3-D nonlinear finite element model of thoracolumbar included four vertebraes,three discs, the ligaments and all joint cartilages and ligaments. By applying physiological load, the range of movement of flexion, extension, rotation and flexor was similar to results of cadaver mechanic experiment.This model gained large range of movement within small load range. With increasing load, the increment of range of movement trended to constant. This model showed apparent nonlinear mechanic feature.The structures of 2 finite element models of the compression fractures of T₁₂ are similar and they showed simila rnonlinear mechanic feature. This model of compression fracture showed the different reseting-effects after imposing reseting-load at different fulcrum. The change of displacement is the most obvious when the reseting-fulcrum is at the top of spinous process of T₁₂ vertebral, the mechanic feature of various parts of the injured vertebral is the most stable, but the stress of the zygapophysial joints is larger.Conclusion: The biomechanical feature of the 3-D nonlinear finite element models of thoracolumbar and thoracolumbar vertebral compression fractures is mainly consistent with true human movement pattern. The models can be further used in biomechanical experiment of thoracolumbar vertebral.The method of establishing the 3-D nonlinear finite element models of the compression fractures based on the ultrathin CT scan datas of normal human is feasible. The reseting-fulcrum should be elected at the top of the spinous process of the injured vertebra, the stress of the zygapophysial joints is large in the course of the reseting, this is one of the reasons of injury of zygapo-physial joints and later low back pain.