Negative biomechanical effects of large grade nuclectomy in the transforaminal endoscopic discectomy increased the risk of adjacent segment diseases: A finite element study

2021 ◽  
Vol 93 ◽  
pp. 141-146
Author(s):  
Rui Cao ◽  
Yanwei He ◽  
Chengmei Qian ◽  
Lin Ma ◽  
Jingchi Li ◽  
...  
Keyword(s):  
Finite Element ◽  
Adjacent Segment ◽  
Finite Element Study ◽  
Endoscopic Discectomy ◽  
Adjacent Segment Diseases ◽  
Element Study

scholarly journals Traditional and Cortical Trajectory Screws of Static and Dynamic Lumbar Fixation- A Finite Element Study

2020 ◽  
Author(s):  
Che-Wei Liu ◽  
Lu-Lin Wang ◽  
Yu-Kun Xu ◽  
Chun-Ming Chen ◽  
Jian-Cyuan Wang ◽  
...  
Keyword(s):  
Finite Element ◽  
Cortical Bone ◽  
Large Diameter ◽  
Fatigue Cracking ◽  
Adjacent Segment ◽  
Finite Element Study ◽  
Pull Out ◽  
Comparison Results ◽  
Flexion Extension ◽  
Element Study

Abstract Background: Two types of screw trajectories are commonly used in lumbar surgery. Both traditional trajectory (TT) and cortical bone trajectory (CBT) were shown to provide equivalent pull-out strengths of a screw. CBT utilizing a laterally-directed trajectory engaging only cortical bone in the pedicle is widely used in minimal invasive spine posterior fusion surgery. It has been demonstrated that CBT exerts a lower likelihood of violating the facet joint, and superior pull-out strength than the TT screws, especially in osteoporotic vertebral body. No design yet to apply this trajectory to dynamic fixation. To evaluate kinetic and kinematic behavior in both static and dynamic CBT fixation a finite element study was designed. This study aimed to simulate the biomechanics of CBT-based dynamic system for an evaluation of CBT dynamization. Methods: A validated nonlinearly lumbosacral finite-element model was used to simulate four variations of screw fixation. Responses of both implant (screw stress) and tissues (disc motion, disc stress, and facet force) at the upper adjacent (L3-L4) and fixed (L4-L5) segments were used as the evaluation indices. Flexion, extension, bending, and rotation of both TT and CBT screws were simulated in this study for comparison. Results: The results showed that the TT static was the most effective stabilizer to the L4-L5 segment, followed by CBT static, TT dynamic, and the CBT dynamic, which was the least effective. Dynamization of the TT and CBT fixators decreased stability of the fixed segment and alleviate adjacent segment stress compensation. The 3.5-mm diameter CBT screw deteriorated stress distribution and rendered it vulnerable to bone-screw loosening and fatigue cracking. Conclusions: Modeling the effects of TT and CBT fixation in a full lumbosacral model suggest that dynamic TT provide slightly superior stability compared with dynamic CBT especially in bending and rotation. In dynamic CBT design, large diameter screws might avoid issues with loosening and cracking.

scholarly journals Traditional and Cortical Trajectory Screws of Static and Dynamic Lumbar Fixation- A Finite Element Study

2020 ◽  
Author(s):  
Che-Wei Liu ◽  
Lu-Lin Wang ◽  
Yu-Kun Xu ◽  
Chun-Ming Chen ◽  
Jian-Cyuan Wang ◽  
...  
Keyword(s):  
Finite Element ◽  
Preoperative Evaluation ◽  
Fatigue Cracking ◽  
Adjacent Segment ◽  
Lumbar Surgery ◽  
Systematic Analysis ◽  
Finite Element Study ◽  
Pull Out ◽  
Flexion Extension ◽  
Element Study

Abstract Background : To evaluate kinetic and kinematic behavior in both static and dynamic CBT fixation a finite element study was designed. Two types of screw trajectories are commonly used in lumbar surgery. Both traditional trajectory (TT) and cortical bone trajectory (CBT) provide equivalent pull-out strengths of a screw. Dynesys fixation of TT screws, but not dynamization of CBT screws, has been used extensively in lumbar surgery. This study aimed to simulate the biomechanics of CBT-based dynamic system for an evaluation of CBT dynamization.Methods: A validated nonlinearly lumbosacral finite-element model was used to simulate four variations of screw fixation. Responses of both implant (screw stress) and tissues (disc motion, disc stress, and facet force) at the upper adjacent (L3-L4) and fixed (L4-L5) segments were used as the evaluation indices. Flexion, extension, bending, and rotation of both TT and CBT screws were simulated in this study for comparison.Results: The results showed that the TT static was the most effective stabilizer to the L4-L5 segment, followed by CBT static, TT dynamic, and the CBT dynamic, which was the least effective. Dynamization of the TT and CBT fixators decreased stability of the fixed segment and alleviate adjacent segment stress compensation. The 3.5-mm diameter CBT screw deteriorated stress distribution and rendered it vulnerable to bone-screw loosening and fatigue cracking.Conclusions: A systematic analysis of the effects of TT and CBT fixation constructs on kinematic and kinetic responses in a full lumbosacral model is currently lacking. This study examined both the static fixation effect and its dynamic counterpart and identified that dynamization of CBT have slightly inferior structural stiffness than dynamic TT and cautious preoperative evaluation is essential if 3.5-mm diameter CBT screws are used. Therefore, 4.5-mm or 5.5-mm diameter CBT screws, or as big as tolerated, are recommended to avoid loosening and cracking.

Finite-Element Study of Biomechanical Explanations for Bone Loss around Dental Implants

2020 ◽  
Vol 30 (1) ◽  
pp. 21-30
Author(s):  
Ali Merdji ◽  
Belaid Taharou ◽  
Rajshree Hillstrom ◽  
Ali Benaissa ◽  
Sandipan Roy ◽  
...  
Keyword(s):  
Finite Element ◽  
Bone Loss ◽  
Dental Implants ◽  
Finite Element Study ◽  
Element Study

scholarly journals Finite Element Study on Calculation of Nonlinear Soil Consolidation Using Compression and Recompression Indexes

2020 ◽  
Vol 10 (14) ◽  
pp. 4737
Author(s):  
Chao Xu ◽  
Suli Pan
Keyword(s):  
Finite Element ◽  
Case History ◽  
Time Dependent ◽  
Discrete Equation ◽  
Soil Consolidation ◽  
Coefficient Of Consolidation ◽  
Finite Element Study ◽  
Nonlinear Consolidation ◽  
Element Study

The coefficient of consolidation is traditionally considered as a constant value in soil consolidation calculations. This paper uses compression and recompression indexes to calculate the solution-dependent nonlinear compressibility, thus overconsolidation and normal consolidation are separated during the calculations. Moreover, the complex nonlinear consolidation can be described using the nonlinear compressibility and a nonlinear permeability. Then, the finite element discrete equation with consideration of the time-dependent load is derived, and a corresponding program is developed. Subsequently, a case history is conducted for verifying the proposed method and the program. The results show that the method is sufficiently accurate, indicating the necessity of considering nonlinearity for consolidation calculations. Finally, three cases are compared to reveal the importance of separating the overconsolidation and normal consolidation. Overall, this study concluded that it is inadequate to consider just one consolidation status in calculations, and that the proposed method is more reasonable for guiding construction.

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