| With spinal instrumentation applied broadly in clinical practice, Spinal instrumentation failure was found. In order to seek the causes of the instrumentation failure, the implant designer and the clinicians did a lot of research on it. The Three-Dimensional finite element model of thoracolumbar vertebrae and its instrumentation model are constructed in our research, comparing the biomechanics characteristics of the angular-screw system and the angular-bar system.Experimentation is a direct means to analyze the behavior of the implant through displacement (degree) response of instrumented segments to applied forces (moments), compared to that of an intact one. However, experimentation has some awkward limitations, such as, 1-Many procedures (number of vertebrae in the segment, boundary condition) used by different authors are nonstandard. 2.Specimens for Experimentation were different. 3. Didn't observe the stress distribution in the vertebrae and in the different parts of the device, etc. These limitations impacted the validity of the experimental result. Otherwise, Twenty years has past when the finite element was first applied in the study of spinal biomechanics, it was the most valuable method to study spinal biomechanics, it can cope with these limitations of the experimentation, for example, it enables the same procedure (number of vertebrae in the segment, boundary conditions) and the same vertebral segment (geometry, mechanical characteristics) to be used for different spinal implant, and for each implant to analyze the influence of different parameters. At the same time, it can observe the stress distribution in the vertebrae and the device, etc. Therefore, a validated finite element would be a powerful simulation tool, for clinician as well as the implant designer.52001Many overseas scholars reported the finite element model of Steffee instrumentation (Goel-VK et al, 1988) and CD instrumentation (Lavaste et al, 1994) and study their biomechanics, but they did not report the finite element model of thoracolumbar fixation. Many domestic scholars reported many about treating thoracolumbar fracture with AF or RF instrumentations, and many about biomechanical research of experimentation with AF and RF instrumentations, However, they did not report the finite element model of AF or RF instrumentation. So we established the finite element models of thoracolumbar vertebrae and thoracolumbar implant in order to compare the stress distribution of AF or RF instrumentations and analyze the causes of implant failure. Then, we can find ways of decreasing the failure of implant.Method and materialThis research was completed in the orthopaedic Department of Zhejiang University School of Medicine. We use constructive software (GS-CAD), which is provided by the CAD chamber of Zhejiang University and the finite element analysis software(ALGOR).1. Construction of thoracolumbar three-dimensional nonlinear geometric and mechanical modelThe fresh adult cadaver is acquired and intercepted T^ LI and L2 to be specimen. The model is constructed in GS-CAD according to the parameters from the specimen measurement. Second, the model is entered ALGOR and amended till satisfaction. The nodes and cells of model are divided according to the common laws of the finite element division. The ligaments and the annulus fibrosis are modeled as TRUSS elements, whose materials is nonlinear, that is, its material properties changes with value of loads; Facet articulation is modeled as General Contact elements, and taken as non-friction between opposing facets and 0.45mm-distance between the articulating surfaces. The intervertebral disc is divided into fiber bands(lamellae), ground substance and nucleus. The hydrostatic characteristics of nucleus pulposus are simulated with a three-dimensional incompressible fluid element represented by its bulk modulus, and the fibers are arranged at average 30 degree to the horizontal in a criss-cross pattern; Others(Cortical bone, Cancellous bone and endplates) are simplifi...
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