Automated Hexahedral Meshing of Femoral Growth Plates

The mechanobiological model requires hexahedral elements aligned within the growth plate stacked in several layers to define transition zones and enable progressive growth simulations for each layer of the growth plate. We developed the GP-Tool to automatically create hexahedral meshes based on the subject-specific femoral geometry. The STL-files obtained from the segmented femurs were used as input for the GP-Tool. A visual overview of the steps to create a mesh with the GP-Tool is shown in Figure 1.
Using MATLAB’s (MathWorks, Natick, MA, United States) principal component analysis (“pca”-function) the main orientation of the growth plate was determined. All parts of the femur were rotated so that growth plates’ main orientation was parallel to the XY plane. The growth plate itself was removed and the part above the growth plate of the proximal trabecular bone was positioned on the part which is below the growth plate. Smoothing of the intersection region was performed with MeshLab (Cignoni et al., 2008 (link)). These steps were necessary to create a continuous mesh to add perfectly aligned hexahedral elements in the growth plate later. Sculpt tool of Coreform Cubit (Coreform, Utah, United States) was used to create a hexahedral mesh with an element size of approximately 1.5 mm. A mesh convergence study was conducted based on three femurs to ensure that the results are not influenced by the number of elements in the mesh (see Supplementary Material). The part above the growth plate was moved to its original position and ten layers with equal height were added and presented the growth plate. Finally, the mesh was optimized to no longer include elements with negative Jacobians. This procedure was performed for each femur of all participants (N = 50) and resulted in meshes of approximately 150.000 nodes and 140.000 elements varying due to different femur sizes.