Automated three - Dimensional finite-element meshing for total hip prosthesis

The finite element method (FEM) is a powerful tool in orthopaedic biomechanics. However, developing a 3-D mesh model in irregular geometry object is a labor intensive works hence limits the usage of the three dimensional approaches for bony objects. This study presents a automatic procedure to generate the three dimensional finite element model of femur and prosthesis system from CT slices and CAD system. Image processing, simulation of stem implantation, three dimensional automesh and determining the material properties are the major phases of this study. Firstly, CT scan is used as the raw input data. A self-developed image processing system was employed to detect the periosteal boundaries and endosteal boundaries of the femur. These femoral boundaries are transferred into a CAD system. A series of stem contours can be obtained and merged into the femoral boundaries within the CAD system. The mesh process is basically a moving nodes of uniform cube approach. The boundaries of each CT slice are superimposed by a uniform grid points. For grid points that are within half grid space of the boundaries, they will be moved to the nearest position of the boundaries. The grid points outside the periosteal boundaries will be discarded. The remaining grid points is then regarded as nodal points of the mesh. A cube will be formed from the corresponding grid points between two adjacent slices, and will be broken to generate the tetrahedral elements thus create the three-dimensional FE mesh. Finally, the material property of each element can be calculated from CT number by a cubic equation.