Recurring Meeting of Cleveland Clinic - University of Utah

Date: March 4, 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. Decide action items for next meeting.
4. Other.

Immediate Action Items:

• Cleveland Clinic (Ahmet)
  • Provide previously obtained results of Open Knee(s) - Generation 1 in passive flexion.
• University of Utah (Steve and Ben)
  • Evaluate the role of menisci constraints on model behaviour, both in terms of predictions and convergence, update the wiki accordingly.
  • Update wiki to provide illustration of splitting files, possibly by creating a new wiki page within the FEBio section.

Notes:

1. Update on in situ strain studies.
   • Steve applied 4% constant in situ strain in the Open Knee(s) - Generation 1 model and conducted a passive flexion following that. The in situ strains were applied in a weak manner. When not enforced the errors between desired and resultant in situ strains appeared to be large. The attempts to enforce in situ strains exactly resulted in convergence problems. While this may be a result of prescription of non-physiological in situ strains, Steve suspects a numerical issue.
   • The next step is to implement in situ strains from Yasin Dhaher's paper. These are provided for different bundles of each ligament. Ahmet also asked to evaluate the changes in knee kinematics in passive flexion to see how sensitive the predicted kinematics is to in situ strain levels. He suspects internal/external rotation will be influence significantly. Steve also observed that when 4% constant in situ strain was applied the joint was rotating.
   • Steve also noted large movement of the lateral meniscus, which was suspected to be causing convergence problems. This behaviour may well be non-physiological and additional constraints to stabilize the meniscus were discussed. The horn insertion site can be distributed rather than utilizing a single point on the tibia for each horn. Ahmet previously conducted studies using three-point insertion for each horn. While meniscus edges were stabilized, large deformation of the lateral meniscus was observed. The other possibility is to increase the circumferential stiffness of the meniscus. The menisci were modeled as orthotropic material yet simulations with different ratios of circumferential vs transverse stiffness were not conducted. Ahmet also noted that adding a transverse ligament to connect anterior regions of menisci may stabilize the lateral meniscus. The medial meniscus can be connected to the medial collateral ligament and both menisci may be attached to the tibia posteriorly to represent the capsule. Such attachments can be in the form of discrete spring elements. Jeff advised Steve to see how other knee models constrained the menisci.
2. Update on other feature implementations.
   • The focus of University of Utah team was primarily on the in situ strain studies (see agenda item above).
3. Decide action items for next meeting.
   • See Immediate Action Items above.
4. Other.
   • Steve has started using file splitting to tackle the Open Knee(s) model. He advises such an approach as it simplifies navigating different model inputs.
   • Ahmet mentioned a study he has done to compare Open Knee(s) - Generation 1 model predictions against literature data on passive flexion kinematics collected on cadaver specimens. He noted the discrepancies in knee rotations particularly at large flexion angles, which were also noted by the University of Utah team. Ahmet will share this study with the Utah group. The study also provides some information on the use of different meniscal horn attachments.