Recurring Meeting of Cleveland Clinic - University of Utah

Date: April 8, 2015

Time: 2:00 PM EST

Means: Conference call

Attendees:

1. Ahmet Erdemir (Cleveland Clinic)
2. Jeff Weiss (University of Utah)
3. Ben Ellis (University of Utah)
4. Steve Maas (University of Utah)

Agenda:

1. Update on in situ strain studies.

   • http://wiki.simtk.org/openknee/Febio/InSituStrain

2. Update on other feature implementations.

   1. Set definitions - http://wiki.simtk.org/openknee/Febio/SetDefinitions

   2. Connector elements - http://wiki.simtk.org/openknee/Febio/RigidBodyMotions

   3. Splitting of FEBio input files
3. Convergence improvements for Open Knee(s) - Generation 1.
4. Decide action items for next meeting.
5. Other.

Immediate Action Items:

• Cleveland Clinic (Ahmet)
  • Start populating the wiki on interpretation of simulation results, particularly from convergence and accuracy perspective.
• University of Utah (Steve)
  • Implement in situ strains from literature to Open Knee(s) - Generation 1 model.

Notes:

1. Update on in situ strain studies.
   • Steve will implement in situ strains reported in Dhaher's manuscript. This may help stabilize internal rotation and therefore lateral meniscus posterior translation. The goal is to define in situ strains at anticipated levels first. For debugging, simulations can be conducted with menisci tied to the cartilage (see discussion on convergence improvements).
2. Update on other feature implementations.
   • Steve updated the wiki to describe splitting of FEBio input files.
   • Steve asked about FEBio features requested by the Cleveland Clinic team and how it may fit to Open Knee future. Ahmet provided a brief description of how each feature may facilitate simulations with the Open Knee(s) and in general, with any musculoskeletal joint. The goal is to establish these models as turn-key solutions to conduct robust simulations supported by FEBio.
3. Convergence improvements for Open Knee(s) - Generation 1.
   • In the Open Knee(s) - Generation 1 model, Steve tied the lateral meniscus not allowing it to move. With that the simulations seemed to be converging when setting static analysis flag. With the lateral meniscus constrained, dynamic simulations had convergence issues. It may be necessary to introduce damping to the system and time integration parameters may be need to be adjusted as the dynamic simulations may be suffering from vibrations. Steve noted that all simulations were conducted using full Newton approach.
   • In relation to meniscus, Jeff noted that the cartilage extends beyond menisci footprints. Ahmet noted that this may be a segmentation error but also it may be physiological (based on dissection of other knees).
   • It may be wise to add soft torsional and linear springs at the center of mass of the femur to stabilize the rigid body degrees of freedom. Steve will run the simulations in the debug mode to see which degrees of freedom may be problematic. He will consecutively try specifying and fixing the 5 degrees of freedom (other than flexion). Ahmet noted that it may be beneficial to look at tibia and femur forces and moments. The discrepancies in these may indicate the problematic degrees of freedom.
   • For convergence analysis, it is fine to run simulations with the menisci tied. Yet, for physiological simulations it is necessary to justify addition of new features or boundary conditions. This will help establish appropriate realism while aiding convergence.
   • The group also discussed comparison of tibia and femur reaction forces/moments for model debugging and interpretation. Documentation of such approaches, e.g., in the wiki, will help the users of the model to understand the limitations and capabilities of the model (and modifications on it) better.
4. Decide action items for next meeting.
   • See Immediate Action Items above.
5. Other.
   • None noted.