| Summary: | 博士 === 國立中央大學 === 機械工程學系 === 101 === There have been many types of implants used to treat various diseases related to lumbosacral instability and deformity. Prior to their clinical use, the in vivo behaviors of the implants can be evaluated by means of biomechanical experiment and numerical simulation. In the field of lumbosacral biomechanics, the finite-element method has been used to evaluate implant-induced effects on the kinematic and mechanical responses at the fixed and adjacent segments. This study first developed intact and degenerative models of the five-segment lumbosacral column. After validation, the intact model served as the comparison baseline and the degenerative model was instrumented with a transpedicular fixation to calculate the load-controlled method (LCM) and ROM-controlled method (RCM) results. Subsequently, a displacement-controlled method (DCM) was proposed by using the nodal displacements of the intact model to guide the vertebral motion of the instrumented model. By using the most efficient controlled method, the current study aimed to investigate the biomechanical effects of fixator stiffness and disc degeneration on the transition and adjacent segments. The degeneration grade of the discs and cord stiffness of the dynamic fixator were varied to investigate the trade-off of the junctional problem at the adjacent segments and motion preservation at the transition segments. The findings of the current study are to provide insight into the device- and surgery-related factors associated with better outcomes of the hybrid fixation. For computational efficiency, the calculation time of the DCM model was seventeen times faster than that of the RCM models. The comparable results and efficient calculation make the DCM the improved strategy for executing the lumbosacral nonlinear analysis. This study also showed that the hybrid fixator can serve as both a motion-preserver and a load-shield for the transition segment. However, the kinematic and mechanical constraints due to the hybrid fixation were inevitably compensated to the adjacent segments. Consequently, the hybrid fixator protected the transition segment but potentially deteriorated the adjacent segments. This study presented the trade-off concept that the protection of the transition segment and the deterioration of the adjacent segments should be balanced. The trade-off stiffness of the flexible cord provides improved rigidity and flexibility of the hybrid fixation and depends on both fixator design and disc degeneration.
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