Based on the CT data and the structure characteristics of the femoral fractures during different healing stages, medical FE models of fractured femur treated with locking compression plate (LCP)were built.Under the physiological load of a standard body weight (70 kg) and the constraint condition,the stress distributions of LCP and fractured femur during healing were calculated by means of three-dimensional finite element analysis (3D-FEA).The results showed that the stress distribution in the LCP and the fractured femur was similar,during the initial stage which there was no newly formed bone or soft tissue in fracture site.The maximum von Mises stress (371.23,272.76 MPa) in the fractured femur was much higher than that in natural femur,and the intensive stress was concentrated mainly in the proximal area of the fractured femur.With the growth of bony callus bone in fracture site,the intensity of stress in proximal femur decreased.Contrasted to the two cases mentioned above,the value of the maximum von Mises stress (68.17 MPa) in bony callus bone stage decreased significantly,and was lower than the safe strength of natural bone.Therefore,appropriate training which is benefitial for the growth to new bone could be arranged for the better rehabilitation.
We observed the effect of vibration parameters on lumbar spine under different vibration conditions using finite element analysis method in our laboratory. In this study, the CT-images of L1-L5 segments were obtained. All images were used to develop 3D geometrical model using the Mimics10.01 (Materialise, Belgium). Then it was modified using Geomagic Studio12.0 (Raindrop Geomagic Inc. USA). Finite element (FE) mesh model was generated by Hypermesh11.0 (Altair Engineering, Inc. USA) and Abaqus. Abaqus was used to calculate the stress distribution of L1-L5 under different vibration conditions. It was found that in a vibration cycle, tensile stress was occurred on lumbar vertebra mainly. Stress distributed evenly and stress concentration occurred on the left rear side of the upper endplate. The stress had no obvious changes under different frequencies, but the stress was higher when amplitude was greater. In conclusion, frequency and amplitude parameters have little effect on the stress distribution in vertebra. The stress magnitude is positively correlated with the amplitude.
A geometrical model of L4-L5 lumbar segment was constructed using a three-dimensional graphics software. Four conditions of the degenerated discs, i.e. light degeneration, moderate degeneration, severe degeneration and complete excision degeneration, were simulated with loading situations using finite element method under the condition of appropriate computational accuracy. By applying a vertical load of 378.93 N on L4 vertebral plate, stress nephograms on joint isthmus under four different working conditions were obtained. The results showed that the contacted area of facet joint was influenced by the degree of intervertebral disc degeneration level, which influenced the mises stress on joint isthmus. It was proved that joint isthmus was the important pressure-proof structure of the back of lumbar vertebra, and the stress values and distribution were related to structural stiffness of the back of lumbar vertebra as well as the contact area of facet joint. The conclusion could be the theoretical reference for the analysis of spinal biomechanics and artificial disc replacement as well.
This study was aimed to compare the mechanical characteristics under different physiological load conditions with three-dimensional finite element model of rigid fixation and elastic fixation in the lumbar. We observed the stress distribution characteristics of a sample of healthy male volunteer modeling under vertical, flexion and extension torque situation. The outcomes showed that there existed 4-6 times pressure on the connecting rod of rigid fixation compared with the elastic fixations under different loads, and the stress peak and area of force on elastic fixation were much higher than that of the rigid fixations. The elastic fixation has more biomechanical advantages than rigid fixation in promoting interbody lumbar fusion after surgery.
Finite element analysis can be used to study the change of the structure and the interior field intensity of human and animal body organs and tissues with simulation experiment. We in our research used finite element analysis software to analyze and solve the spinal cord surface potential problems, and investigated the transmission features of signals generated by interneurons in spinal nerves which were related with body motion control and sensory processing. A three dimensional model of electrical source in rat spinal cord was built, and the influence on potential distribution on spinal cord surface caused by position changes of electrical source in transverse direction and dorsoventral direction were analyzed and calculated. We obtained the potential distribution curves of spinal cord surface and found that the potential distribution on spinal cord surface showed monotone. In addition, potentials of some registration points were smaller than that of registration points around.
Based on the surgical model using transforaminal lumbar interbody fusion (TLIF) to treat lumbar spondylolisthesis, this paper presents the investigations of the biomechanical characteristics of cage and pedicle screw in lumbar spinal fusion implant fixed system under different combinations with finite element method. Firstly, combining the CT images with finite element pretreatment software, we established three dimensional nonlinear finite element model of human lumbar L4-L5 segmental slight slippage and implant under different fixed combinations. We then made a comparison analysis between the biomechanical characteristics of lumbar motion range, stress distribution of cage and pedicle screw under six status of each model which were flexion, extension, left lateral bending, right lateral bending, left axial rotation and right axial rotation. The results showed that the motion ranges of this model under different operations were reduced above 84% compared with those of the intact model, and the stability of the former was improved significantly. The stress values of cage and pedicle screw were relatively larger when they were fixed by single fusion device additional unilateral pedicle screw, but there was no statistically significant difference. The above research results would provide reference and confirmation for further biomechanics research of TLIF extracorporal specimens, and finally provide biomechanical basis for the feasibility of unilateral internal fixed diagonal intervertebral fusion TLIF surgery.
This study aims to investigate the range of motion (ROM) and the stress variation in the intervertebral disc and the vertebral body on adjacent segments and the influence of force transmission mode after the dynamic cervical implant (DCI) surgery. Two types of surgery, DCI implantation and interbody fusion were used to establish the finite element model of the cervical C5, 6 segment degeneration treatment. The ROM and the adjacent discs and vertebral body stresses of two procedures under flexion, extension, lateral bending and axial rotation working conditions were analyzed. The results showed that ROM of the surgical segment in DCI model was well preserved and could restore to the normal ROM distributions (reduction of the amplitude was less than 25%), and the kinetic characteristics of adjacent segments was less affected. In fusion surgery model, however, ROM of the surgical segment was reduced by 86%-91%, while ROM, disc stress and vertebral stress of adjacent segments were increased significantly, and stress of the C5 vertebral body was increased up to 171.21%. Therefore DCI surgery has relatively small influence on cervical ROM and stress. The study provides a theoretical basis for DCI and fusion surgery in clinic.
Due to the superior pigment and high flexural strength, machinable lithium disilicate ceramics can be used as a monolithic crown or veneering porcelains on the zirconia core to form the all-ceramic crowns by sintering or bonding procedures. This paper reports the research on the differences in stress distributions amongst these three types of all-ceramic crowns under typical loading conditions. Three-dimensional numerical models of the restored crown based on the first mandibular molar were developed. The vertical concentrated load and 8-point uniformly distributed load were applied, respectively. The maximum stress and stress distribution were resulted from finite element evaluation. It was found that the maximum tensile stress in 3 types of restored crowns subjected to the concentrate load was less than the flexural strength of IPS e.max. The stress distributions in the sintered and bonded double layered crowns were basically identical, and different from the monolithic crown. The stress magnitude in veneer porcelain of the bonded crown was greater than that in the sintered crown. The use of IPS e.max computer aided design monolithic crown as molar restorations should be careful to avoid high stress as the cyclic stress is a concern of fatigue which may influence the longevity of the restored crown. The bonded double layer crowns bear greater risks of veneer chipping compared with the sintered crowns. The conclusions of this study provide helpful guidelines in clinical applications for preparation of computer aided design/computer aided manufacture lithium disilicate all-ceramic restorations.
Objective To investigate the validity of improving the femur’s mechanical characteristics by implanting calcium phosphate ceramic screws after removing dynamic hip screw (DHS). Methods The three dimensional finite element model of the femur was built based on the CT scanning of a normal male volunteer. Then the models of the femur with and without DHS were established. According to calcium phosphate ceramic screws with porosity and apparent elastic modulus, 80% and 0.1 GPa were set as group A, 50% and 1.0 GPa as group B, and 30% and 1.5 GPa as group C. Von Mises stress distribution and maximum stress were recorded when the joint was maximally loaded in a gait cycle. Results The Von Mises in normal femoral shaft was uniform; no phenomena of stress concentration was observed and the maximum stress located at the joint load-bearing site of the proximal femur. The stress concentration was observed in the femur without DHS, and the maximum stress located at the distal femur around the screw hole. By comparing several different calcium phosphate ceramic screws, the stress distribution of group B was similar to normal femur model, and the maximum stress located at the joint load-bearing site. The other screws of groups A and C showed varying degrees of stress concentration. Conclusion Implanting calcium phosphate ceramic screw can improve the mechanical characteristics of the femur after removing dynamic hip screw, and the calcium phosphate ceramic screw with 50% porosity and 1.0 GPa apparent elastic modulus is suitable for implanting.
The risk of vertebral cortical shell fracture increases with aging. However, it remains unclear how aging contributes to cortex fracture at present. The aim of this study is to make understanding of the mechanism of how the spinal aging influences the cortical shell strain. Two finite element (FE) models of spinal segments (mildly and fully aged) were created, and then were compared to the FE models of the healthy spinal segment. The FE models of the aged spinal segments were generated by modifying both the geometry of the intervertebral disc (IVD) and the material properties of the spinal components. To find out under which case the cortical shell strain was influenced more, we created two types of FE model comparison methods: one with changes only in the spinal material properties and the other with changes only in the IVD geometry. The results showed that the cortical shell strains increased with aging and that compared to the changes of IVD geometry, the changes of spinal material property have a higher influence on the cortical shell strains. This study may suggest that for the prevention and treatment of vertebral cortex fracture, the augmentation of the vertebral body is a more effective treatment.