FEBio

• 1: CAD Modeling Instructions for Pelvic Hip Fracture
• 2: Meshing Instructions for Hip Model
• 3: Working with Simmetrix Meshes

1 - CAD Modeling Instructions for Pelvic Hip Fracture

Note: Ensure that you follow the steps faithfully to avoid issues and achieve desired results

Step 1: Opening and Preprocessing in Autodesk Meshmixer

1. Open M11_cg_bone_lpelvis.obj in Autodesk Meshmixer.
2. Select the entire geometry.
3. Navigate to Edit > Remesh to reduce the chance of overlapping during offsetting.
4. Accept the Remesh operation.
5. Continue with Edit > Extrude > Offset +1.77 mm (direction: normal).
6. Select the geometry again and perform Edit > Remesh (optional but beneficial).

Step 2: Exporting and Transferring to Siemens NX

1. Export the model as an .obj file.
2. Transfer the file to Siemens NX on SCOREC computers using WinSCP or hard drive.
3. Save and close the file to individually save convergent bodies as separate .prt files.

Step 3: Performing Subtractions in Siemens NX

1. Open one file and import the second (outer and inner).
2. Navigate to File > Start > Modeling.
3. Select the outer part and use the Subtract operation with settings:
   • Subtract Tool from Target. Keep Tool operation.*
4. Repeat the subtraction with the sacrum until a full shell model is created.

Step 4: Processing the Sacrum Shell

1. To remove the right half of the sacrum: Place a Datum CSYS in the middle of the sacrum shell using Home > Datum CSYS and position the datum such that there is left-right symmetry.
2. Trim the body using Trim Body command after selecting the appropriate plane. You may have to select the Reverse Direction option to leave the desired left half remaining.
   • It is advised to trim the cancellous and cortical parts separately.
3. Save as a .prt.

Step 5: Facet Cleanup and Hole Insertion

1. In NX, Open the cartilage (m11_cg_jnt_lsi.obj) and save it as a part file.
2. Create a new model in Siemens NX and ensure that units are in mm.
3. Import the Sacrum, Cartilage, and Pelvis parts.
4. Use Facet > Cleanup Facet Body to clean mesh.
5. Delete all minor extra parts that may appear.
6. Add a fracture to the sacrum (Note: trim body command would be more efficient, but has proven to be problematic with regard to the meshing)
   • First, duplicate the entire geometry as it currently exists and make sure its copy is superimposed upon the original
   • Create another Datum CSYS, place it where shear would occur
   • Create a sketch of a large square of arbitrary size, as long as it encompasses the geometry
   • Extrude it in one direction (right if observing from the front) such that it covers half of the sacrum and all of the pelvis
   • Use the subtract command to subtract the box from the part of the bone (choose one of the superimposed copies) which it overlaps
   • Repeat the process for the other half, this time deleting from the other superimposed half
   • This will leave you with one right side and one left side, leaving you with the geometry you had after Step 4, but with a “fracture”
7. Insert a hole:
   • Place a Datum CSYS and then Create Sketch on Plane.
   • Draw a rectangle going into/through sacrum (~100mm length, 3.66 – 3.67mm radius).
   • Revolve the rectangle
   • Select the cylinder and use Facet Body from Body to make the new cylinder convergent.
   • Use Subtract Tool to remove the cylinder from the bone model (one part at a time).
   • Repeat for the second hole, which should not be parallel to the first.

Step 6: Inserting Screw and Final Steps

1. Open the screw (screw-7-74.prt) and remove the Split Bodies and Datum Planes.
2. Import the updated screw part using Assemblies > Add Component.
3. Align the screw to the hole using Assembly constraints (Touch Align the centerlines first and then use Distance Align).
4. Save the entire model as a .prt file.
5. Export the final model as a Parasolid binary file .x_b

2 - Meshing Instructions for Hip Model

1. Importing Geometry:

   • Open SimModeler
   • If the file is in parasolid format, go to File → Import Geometry. For files in .obj or .stl format, choose Import Discrete Data.

2. Preparing for meshing:

   • Navigate to the Modeling tab, choose Delete Parts, and select the screws.
   • In the Meshing tab, click on Generate Mesh. Uncheck “Structured Mesh” and proceed. Upon successful generation, view the mesh by selecting Show Mesh, which creates an .sms file. (Remember to return to the .smd file for generating a new mesh if required.)

3. Refining Mesh:

   • Use Mesh Attributes located on the right-hand side of the screen.
   • The following chart represents some suggested Mesh Attributes and corresponding values:

     Type	Sub-Type	Value
     Mesh Size	Absolute	0.001
     Mesh Curvature Refinement	Absolute	0.005
     Volume Shape Metric	Aspect Ratio	3.0
     Allow Refinement For Shape	Relative	0.0001

   • After making refinements, regenerate the mesh to incorporate the changes.

4. Quality Check:

   • Assess the quality of the mesh by going to the .sms file and navigating to the Display Tab.
   • Click Mesh Stats and scrutinize the Aspect Ratio.

5. Exporting Mesh:

   • To export the mesh, navigate to File > Export Mesh.
   • Save the file if not done previously.
   • Choose the export format as Abaqus 3D (.inp).

6. Meshing Screws Separately:

   • Follow the same steps as for the bone meshing process for the screws.

3 - Working with Simmetrix Meshes