Synopsis

The overall goal of this study is to assess the effects of variations in patella cartilage surface topology due to image segmentation attempts by different users on finite element model predictions.

Preliminary Proposal: Proposal.pdf (will be moved to repository and modified)

Use Case

This use case aims at: a) taking multiple image segmentation attempts (proposed: 6) for patellofemoral joint, b) using the exact same set of tools and protocols and build surfaces, meshes and models and, c) for a given loading scenario (similar to patellofemoral joint testing for the same specimen) comparing the peak stresses on the patella cartilage.

Simulation Aims

• To assess whether segmentation variability due to different users leads to significant variations in finite element model predictions.
• Secondary aim: assessing effect of material model variations along with surface topology on finite element predictions.

Model

• Multiple models will be developed for oks001 from several segmentation attempts.

• https://simtk.org/svn/openknee/app/SegmentationVar/src

Inputs

• 45 degree flexion angle and 600 N quadriceps load. (proposed, may be changed).

Outputs

• Time histories of patella cartilage stress behavior.

Simulation Conditions

• TBD

Team Members

• Snehal Chokhandre - study planning, model development, execution of simulations and post-processing, lead authorship in publications
• Ahmet Erdemir - overall supervision

Progress

• First attempt to manually create a simple compression model for patella and femur cartilage. Geometries generated by Craig for oks001 (smoothed) were used for this trial. Both the cartilage geometries were reoriented in Blender to overlap each other and for easier application of boundary conditions. Femur cartilage also truncated in the region not overlapped by the patella cartilage.
  • Manual meshing and FEA procedure:
    • Geometries imported in Salome (stl files created from Slicer 3D, smoothed surfaces)
    • Tetrahedral meshes and node sets created in Salome. Exported as .unv files
    • Converted .unv to .inp files using unv2abaqus.py.
    • Removed surface elements from the .inp file using text editor before importing in FEBio Preview.
    • Imported .inp files in FEBio Preview, applied boundary conditions, defined materials (Mooney-Rivlin), defined contact, exported as .feb.
    • Ran simulation using FEBio and results visualized in FEBio Postview.

cartfemcomp.bmp

Source Code Repository

https://simtk.org/svn/openknee/app/SegmentationVar/

Data

https://simtk.org/svn/openknee/app/SegmentationVar/dat/

Model Customization

https://simtk.org/svn/openknee/app/SegmentationVar/src/

Simulations

Post-Processing

https://simtk.org/svn/openknee/app/SegmentationVar/sol/

Publications

https://simtk.org/svn/openknee/app/SegmentationVar/doc/

References