The main objective of this project is to make a parametric design of an intervertebral artificial lumbar disc using FE software (ANSYS) in APDL language (ANSYS parametric design language) and then use that software to study the structural response of the intervertebral disc in different situations. First of all the functions of the real intervertebral disc and its structure are going to be exposed, then continue with the explanation of the intervertebral artificial disc and its parameters. After the explanation modified artificial disc with thicker brim inlay is going to be analyzed under different loads studying its response. Then the disc is going to be inserted in the intervertebral space (L4-L5) of a model of the lumbar spine and it is going to be analyzed under a normal and a combined (vertical and horizontal) load state in two different positions, the correct one and a wrong one.
To achieve a new method for predicting the result of disc replacement or to predict biomechanics of lumbar (or any other skeletal segment) by finite element model analysis, its necessary to follow an organized procedure including 3D bone model, meshing the proposed model, designing an artificial implant and simulation of loading condition. In this study we try to explain the whole procedure step by step from importing the CT image to analysis of lumbar section with designed implant. First it's explained how the 3D model can be made based on the CT image using MIMICS software and some details related to simulation of the skeletal model by this software will be released. Second part shows the tutorial method for importing proposed model in ABAQUS software and how it can be analyzed. This step by step tutorial is helpful in lumbar biomechanics and creating human body skeletal model. Also it is useful to achieve a perfect procedure for creating and analyzing lumbar disc implant.
Relative motion at interacting implant surfaces will generate wear debris over time. Bio-tribological tests serve as an effective pre-clinical tool to investigate device wear characteristics. Wear debris evaluations for artificial discs are done in simulators using the currently published ASTM/ISO loading profiles. However, these tests can primarily compare wear related parameters of one disc design against another as opposed to an in vivo scenario. Additionally, these experiments are time consuming, expensive and labor intensive procedures. Current wear testing standards for artificial discs do not account for parameters such as the influence of anatomic structures and variations in the surgical procedures for disc placement. However, appropriate parametric mathematical modeling may help assess the contributions of these parameters to implant wear. The objective of this study is to address the above mentioned factors and to simulate in-vivo wear parameters as far as practicable. In this approach, the wear phenomena of the total disc replacement (for two different designs - metal on metal and metal on polymer) placed in a ligamentous functional spinal unit (FSU), as opposed the disc alone analyses conducted previously by other researchers was simulated. The models were further modified by sequential addition and removal of spinal structures in order to understand the role of each element with respect to the wear outcome. Furthermore, the effect of the implant placement was studied. This was followed by comparative analyses of load versus displacement control test methodology. A significant difference was noted between the implanted and standalone condition. The standalone test cases were in agreement with the published literature, while the implanted scenario replicated some of the retrieval failure modes. Lift-off at the device interface was observed at the implant interface which was found to be a function of facets and muscle forces. This phenomenon was also reported by other researchers, thus supporting our conclusion. The design factor was found to have more effect in comparison to the material combination. Also, implant positioning demonstrated that wear is sensitive to the device placement. Additionally, during the analysis displacement control mode led to higher wear in comparison to load control for both of the implants. We can summarize by stating that this study demonstrated the need to simulate implant wear in ligamentous finite element model in order to replicate failure modes that are observed during retrievals. Surgical factors are thus crucial with respect to the wear performance of the implant and so should be planned carefully.
To conclude, this study highlighted that cervical disc replacement with both the Bryan and Prestige LP discs not only preserved the motion at the operated level, but also maintained the normal motion at the adjacent levels. Under hybrid loading, the motion pattern of the spine with a TDR was closer to the intact motion pattern, as compared to the degenerative or fusion models. Also, in the presence of a pre-existing fusion, this study shows that an adjacent segment disc replacement is preferable to a second fusion.
