A Novel Parametric Approach for Generating Subject Specific Lumbar Vertebral Bodies

Analysis of the mechanical response of the lumbar vertebral body (VB) under certain loading conditions requires a numerical model, which is the building block directly used by finite element method (FEM). Yet, such model comes with drawbacks to deal with in the generation process. The difficulties are related to lacking data integrity provided by subject-specific computed tomography (CT) scan. In order to get through the obstacles, deterministic nature of the parametric computer-aided design (CAD) modeling is adopted. Six parameters, which create a parametric curve on a cross-sectional slice image of a VB; are optimized such that best fits are obtained on fifteen slices grouped as three for each Ll, L2, L3, L4, and L5 VBs. Then, total of 72 construction points necessary to create fifteen contours, in an open-source CAD software called FreeCAD, are transformed from fifteen slice images to a global Cartesian coordinate system (CSYS) by the transformation matrices. After transforming construction points, groups of three contours are lofted to create the lumbar CAD model including only VB section. Finally, this model is compared with another parametric model in terms of Hausdorff distance (HD).