Establishment And Verification On Three-Dimensional Finite Element Emulation Model Of Human Foot And Ankle

Objective:According to CT and MRI cross-sectional images of a healthy male volunteers’ foot-ankle, with the help of Mimics, SolidWorks, HyperMesh and Abaqus software, to establish three-dimensional finite element emulation model of normal human foot-ankle with fine anatomical structures. Furthermore, its effectiveness must be verified, so it can provide a reliably digital platform for the study of the foot-ankle biomechanics, the simulation of all kinds of foot-ankle injury as well as internal fixation operations.Methods:(1) The subjects and data acquisitionChoose a healthy subjects, by physical examination and X-ray examination found no foot disease, then was scanned by 64-slice CT and 3.0T MRI, obtaining 1087 2D-CT slices and 366 2D-MRI slices. All the slices were saved in the format of the DICOM and burned to a CD.(2) The establishment of three-dimensional finite element emulation modelThe scanned images were fully imported into the medical image processing software of Mimics 15.0. According to the data, a three-dimensional model of the foot-ankle bones, cartilage and surrounding soft tissue were established by threshold segmentation automatically or manually. Outcome was saved in the format of point cloud. Then the point cloud data was imported into the reverse engineering software SolidWorks2014, using the plug-in of Scan To 3-D to generate geometric model and rebuild assembly. Outcome was saved in the format of Parasolid. The solid model of the foot-ankle were then processed in the software of HyperMesh12.0. Based on foot ligament anatomic information, the ligaments were established using Truss element and Springs element, as were as reconstructed the foot cartilage. Then the models were meshed, given material parameter, set boundary condition and loading. All the finite element pre-treatments completed, the models were imported into the FE software ABAQUS for emulation analysis.(3)Set the loading, Boundary and contact of the finite element modelTo emulate the neutral phase of gait on the foot-ankle model in ABAQUS software, the superior surface of the soft tissue, distal tibia and fibula was entirely constrained while the foot muscle force directly applied on the corresponding node, muscle direction confirmed by corresponding tendon anatomy position, and through the support plate upward continuous displacement to simulate the foot reaction. To simulate the friction contact between the joint surfaces and the foot-ground interface, ABAQUS automated surface-to-surface contact option was used, the friction coefficient was set to 0.01 and 0.6, respectively.Results:(1)This research established three-dimensional finite element emulation model of foot-ankle, containing 205203 elements and 48748 nodes, which was made up of 29 bones,113 ligaments, each articular cartilage and surrounding soft tissue. The three-dimensional finite element emulation model has complete structure, realistic shape, and material properties is relatively accurate, moreover the contact boundary, load were set reasonable, which is well meet the needs of foot-ankle finite element simulation analysis, at the same time by using visualization technology can obtain 3-d information of arbitrary angle.(2) With comparing with the related research results at home and abroad can be seen that the model has high emulation, verifying its effectiveness, so that it could be used for further experimental study and clinical application. Through emulate and analysis the neutral phase of gait, plantar pressure peak appears at below of the first metatarsal head, followed by below the heel; From the talonavicular joint, cuneonacicular joint and 1-3 metatarsal bone as the main bearing parts, these parts of the bone stress distribution is relatively concentrated, von Mises stress value is bigger; stress distribution of the surface in the ankle under tibia was mainly concentrated in the central and anterolateral.Conclusions:In this research, using CT and MRI images we established three-dimensional finite element emulation model of foot-ankle which based on the softwares of Mimics、 SolidWorks、HyperMesh and ABAQUS. The model has real appearance, fine structure, well mechanical performance. In addition, the model had advantages of convenient, quick and accurate. This model which directly used Mimics, SolidWorks modeling, eliminated human disturbance to the greatest extent, greatly reduced error, and restored the real geometric model of bone. HyperMesh12.0 as professional mesh software had the characteristics of dividing the unit high quality, distributing unit size reasonably, more accurate results, and agreeing with the entity model form. Ligament, cartilage model was established and the model was more closed to the entity on the mechanical properties. Furthermore, the organizational structure in the simulation calculation can be a very good play to their respective functions. Its effectiveness is fully verified. Therefore, this model can be used as a dependable digital platform on foot biomechanics research, simulating all kinds of foot injury and internal fixation operation.