Biomechanical Evaluation of Cortical Bone and Traditional Trajectories for Lumbar Single Level Segment Fixation

Background: The aim of this study was to evaluate the biomechanical stability of a lumbar internal fixation system with 3 different fixation techniques by the establishment of a three-dimensional finite element (FE) model of lumbar single level fixation.Methods: A three-dimensional osseoligamentous nonlinear FE model of osteoporosis lumbar 4-5 (male, aged 57 years, height 170 cm, weight 70 kg, bone mineral density T value -2.8SD) was built to detect the biomechanical stability of an internal fixation system with the following 3 screw trajectories: traditional pedicle screw trajectory fixation (TT), cortical bone trajectory (CBT) screw and hybrid pedicle screw fixation (CBT + TT). The location and area of maximal equivalent stress and the angular displacement of this lumbar model with different screw trajectories were measured in anterior bending, posterior extension, lateral bending and during rotation.Results: The angular displacement of this lumbar model with the 3 different screw trajectories was similar, all of which could restrict the angular displacement of lumbar vertebrae. The maximal equivalent stress was located at the border of the CBT screw and rod, with the hybrid screw fixation technique in axial rotation. Conclusion: The use of CBT and TT screws in lumbar internal fixation had similar stability. The CBT screw could be an alternative solution to lumbar short-segmented fixation, but temporary immobilization would be required to avoid the failure of CBT screw fixation due to the increasing stress in position of extensive lateral bending and rotation.

Kinematics and Mechanical Properties of Knees following Patellar Replacing and Patellar Retaining Total Knee Arthroplasty

Knee injury is a common medical issue. A full understanding of the kinematics and mechanical properties of knees following total knee arthroplasty (TKA) repair utilizing patellar replacement (only the base of the patella is replaced) versus patellar retaining surgical techniques is still lacking. In the current paper, we investigated magnetic resonance (MR) imaging data from knees repaired by these two methods and evaluated total knee models created using imaging reconstruction technology that simulated gait conditions. Results revealed that patellar replacement had little influence on tibiofemoral kinematics, although the tibia-surface equivalent stress increased slightly. By contrast, patellar replacement had a significant influence on the patellofemoral joint; patellar internal rotation, external rotation, and medial-lateral translation were all increased. Moreover, the stress distribution on patellar prostheses was altered, resulting in an increased surface maximal equivalent stress on the corresponding area. Moreover, during the gait cycle, we found that the area with maximal equivalent stress shifted its position. Finally, the patellofemoral joint showed decreased motion stability. From the view of kinematics and mechanics, this paper suggests that patella should be retained during TKA if it is possible. The present study presented approaches and technologies for evaluating kinematics and mechanical properties of total knee joint after TKA under gait loads.

Simulation Research of Banded Wedge and Synchronous V Belt Drive Based on ANSYS Workbench

For cutting down the stress and displacement of banded wedge and synchronous V belt drive in the transmission process, promoting the transmission mechanism, and improving quality of the belt drive, the working principle of the transmission mechanism was introduced briefly. The three dimensional solid model of the transmission mechanism constituted in pro/e; the main parameters of the model were set using ANSYS Workbench. And then the serialization simulation analysis of the transmission mechanism was achieved when the tension force is located in the point of the V belt exiting meshing with the driven wheel; the cloud diagram of Von Mises stress and the maximal Von Mises stress and total deformation of the transmission mechanism were elicited. The simulation results were analyzed. The simulation results show that the maximal equivalent stress and maximal total deformation of the transmission mechanism are determined by the size of the tensioning force when the active force is small. Augmenting the active force of the transmission mechanism the maximal equivalent stress increases effectively and the maximal total deformation changes little when the active force is large. Reducing becomingly the tensioning force in ensuring natural belt drive shall reduce effectively the maximal Von Mises stress of the transmission mechanism. Adjusting opportunely the location of the tensioning force the total deformation of the transmission mechanism reduces effectively.

The Equivalent Stress Contrast Analyse of Inverse Structure and General Structure Asphaltum Pavement

Based on the multi-layer elastic system theory , it was elicited that the top basic-layer rigidity was a main determinate factor for the surface-layer bottom maximal equivalent stress. And the more basic-layer rigidity, the less surface-layer bottom maximal equivalent stress, showing the more the partake action of basic-layer to the surface-layer bearing axis load. On the side, bearing the same axis load, the stress passed to groundwork from the inverse structure was most compared with the other structures. So the inverse structure has no predominance in the road structure design.