ABSTRACT
Objective To establish 5 different finite element models of the proximal femur based on CT images, and analyze the influences of element size on materials distribution and biomechanical behavior of the proximal femur model. Methods The proximal femur was scanned by spiral CT. The images, stored as DICOM format, were extracted by Mimics to obtain 3D geometric data, and then meshed separately by Mimics, 3-Matic and ICEM software to establa voxel element model, a tetrahedral element model and 3 hexahedral element model (with element size of 2, 1, 0.5 mm). These meshed models were assigned materials by Mimics, and their mechanical behavior was analyzed by Abaqus eventually. Results For the proximal femur model with material assignment based on CT images, the influence of element size on the total mass of all the 5 models was not significant. The nodal Mises stress and nodal displacement along the same path in 5 models showed a similar tendency, while the Mises stress at each node displayed an obvious deviation. The nodal Mises stress in the hexahedral element model with the element size of 0.5 mm showed accordance with the voxel element model. Conclusions The element size has a small influence on the total mass and nodal displacement when the material assignment is attributed to the model based on CT gray values, while decrease in the element size will affect the materials distributions and stress distributions of the model. When the element size of the proximal femur model is close to its voxel size, the mass distributions and mechanical behavior of the femur can be preferably reflected.
ABSTRACT
Objective To evaluate biomechanical differences between anterior titanium plate internal fixation and posterior pedicle screw internal fixation for treating type Ⅱ unstable Hangman’s fracture by finite element analysis. Methods An intact finite element model of the upper cervical spine (C0-3) was established and validated, and an unstable model was also established. Two different internal fixation models, i.e. anterior titanium plate+Cage with bone graft (Plate+Cage) and C2 pedicle screws+C3 lateral mass screws (C2PS+C3LMS) were established, respectively, based on the unstable model. The vertical load of 40 N was applied on the occiput to simulate head weight and 1.5 N•m torque was applied on the occiput to simulate loading conditions of flexion, extension, lateral bending and rotation. Range of motion (ROM) of C2-3, force pathway and strain at the fractured line were calculated and analyzed. ResultsCompared with the unstable model, the Plate+Cage model could decrease the ROM by 92.4%, 97.1%, 96.5% and 90.0%, while the C2PS+C3LMS model could decrease the ROM by 88.6%, 90.2%, 95.7% and 90.3%, in flexion, extension, lateral bending and axial rotation, respectively. The maximum stress of the Plate+Cage model was smaller than that of the C2PS+C3LMS model under 4 loading conditions. Conclusions The anterior Plate+Cage fixation possesses better stability than the posterior C2PS+C3LMS fixation in flexion and extension, while both fixation methods show similar stability in lateral bending and axial rotation. The anterior Plate+Cage fixation is more reasonable in structure and stress distributions, and can achieve reduction, decompression, fixation and fusion in one step, thus it is an effective operative procedure for treating typeⅡ Hangman’s fracture.
ABSTRACT
Objective To develop the three-dimensional (3D) finite element (FE) models of pelvis and fracture fixation, and test their validity. Methods Based on CT scan images, the 3D FE model of the pelvis was built by software of Mimics, ANSYS ICEM, Hypermesh and ABAQUS. A uniformly distributed load of 600 N was applied in vertical direction on the upper lamina of S1 vertebrae to simulate the stresses on the pelvis in standing position and to verify the validity of the pelvis model. T-shaped acetabular fracture models with 3 types of fixation were also established to verify the validity of internal fixation. ResultsBoth the stress and displacement distributions were found to be bilaterally symmetrical on the pelvis in standing position, with the Von Mises stresses mainly distributed in the beginning of arcuate line, pubic branch and posterior-superior area of acetabulum. The largest displacement occurred in the center of the sacral crest, and became relatively smaller in iliac fossa and femur, which was reduced gradually to the femur. Each of the three fixation types in acetabulum showed good biomechanical stability. Conclusions The established hexahedral grid-3D FE model can accurately simulate mechanical properties of the femur in standing position, which would provide an intuitive basis for clinical study.