TableOfContents

Synopsis

The overall goal of this case study is to understand convergence characteristics of Open Knee(s) - Generation 1 model to conduct simulations in an efficient and effective manner.

Use Case

The case relies on simulations of varying levels of tibiofemoral joint loading to evaluate the performance of the model in terms of convergence while reasonably predicting joint mechanics. Convergence is defined by the ease and speed of simulations. Relative predictive accuracy evaluates changes in predicted joint kinematics and tissue stress-strain distributions.

Simulation Aims

Model

The model is based on Open Knee(s) - Generation 1 model, which was updated for FEBio version 2.1:

Inputs

The loading and boundary conditions relies on prescribed time histories of movement and loading of the tibiofemoral joint (six degrees of freedom) for various loading scenarios (see Simulation Conditions):

Outputs

Simulation Conditions


Use Cases


max_retries & max_refs

Parameter permutations:

Converged:

Ranking:

  1. max_retries = 5, max_refs = 20
  2. max_retries = 20, max_refs = 20

both have similar results

Results: https://simtk.org/svn/openknee/app/Convergence/sol/max_retries_refs_1/


flexion angle & Anterior-Posterior (AP) force

SET 1

Parameter permutations:

Converged:

Non-converged:

Results: https://simtk.org/svn/openknee/app/Convergence/sol/flexion_AP_1/

SET 2

Parameter permutations:

Converged:

Non-converged:

Results: https://simtk.org/svn/openknee/app/Convergence/sol/flexion_AP_2/


flexion angle & Internal-External (IE) torque

SET 1

Parameter permutations:

Converged:

Nonconverged

Results: https://simtk.org/svn/openknee/app/Convergence/sol/flexion_IE_1/

SET 2

Parameter permutations:

Nonconverged:

Results: https://simtk.org/svn/openknee/app/Convergence/sol/flexion_IE_2/


flexion angle & Varus-Valgus (VV) torque

SET 1

Parameter permutations:

Converged:

Nonconverged:

Results: https://simtk.org/svn/openknee/app/Convergence/sol/flexion_VV_1/

SET 2

Parameter permutations:

Converged:

Nonconverged:

Results: https://simtk.org/svn/openknee/app/Convergence/sol/flexion_VV_2/


SPRING SETS, 90 degree passive flexion, 1.0 s, ramp-only

tf_joint_FEBio_v2.feb, repository revision 1103

Load curve: ramp only (without hold as in original version)

Passive flexion, 90 degrees

Total time = 1.0 s

NONE CONVERGED!!!

SUMMARY:

Spring Set

None

Transverse

Transverse

Transverse

Medial

Medial

Medial

Capsule

Capsule

Capsule

Stiffness (N/mm) / spring

0

33.3

66.6

100

33.3

66.6

100

33.3

66.6

100

# Springs

0

3

3

3

137

137

137

130

130

130

Total Stiffness (N/mm)

0

100

200

300

4566.6

9133.3

13700

4333.3

8666.6

13000

Fraction Complete

0.141834

0.666360

0.827006

0.883352

0.859743

0.909037

0.978855

0.507349

0.444903

0.584906

Flexion achieved (deg)

12.8

60.0

74.4

79.5

77.4

81.8

88.1

45.7

40.0

52.6

NO SPRING SETS

Grood-Suntay Kinematics:

attachment:no_springs_flexion_90.png

Transverse Ligament

33.3 N/mm / spring

attachment:transverse_33.3_flexion_90.png

66.6 N/mm / spring

attachment:transverse_66.6_flexion_90.png

100 N/mm / spring

attachment:transverse_100_flexion_90.png

Medial Ligament

33.3 N/mm / spring

attachment:medial_33.3_flexion_90.png

66.6 N/mm / spring

attachment:medial_66.6_flexion_90.png

100 N/mm / spring

attachment:medial_100_flexion_90.png

Joint Capsule

33.3 N/mm / spring

attachment:capsule_33.3_flexion_90.png

66.6 N/mm / spring

attachment:capsule_66.6_flexion_90.png

100 N/mm / spring

attachment:capsule_100_flexion_90.png

SPRING SETS, 45 degree passive flexion, 1.0 s, ramp-only

tf_joint_FEBio_v2.feb, repository revision 1103

Load curve: ramp only (without hold as in original version)

Passive flexion, 45 degrees

Total time = 1.0 s

CONVERGED!!!

Flexion achieved = 45 degrees

SPRING SETS, 90 degree passive flexion, 2.0 s, ramp-only

tf_joint_FEBio_v2.feb, repository revision 1103

Load curve: ramp only (without hold as in original version)

Passive flexion, 90 degrees

Total time = 2.0 s

NONE CONVERGED!!!

SUMMARY:

Spring Set

None

Transverse

Transverse

Transverse

Medial

Medial

Medial

Capsule

Capsule

Capsule

Stiffness (N/mm) / spring

0

33.3

66.6

100

33.3

66.6

100

33.3

66.6

100

# Springs

0

3

3

3

137

137

137

130

130

130

Flexion achieved (deg)

78.3

73.8

56.2

79.9

40.5

66.6

60.3

77.4

76.5

42.3


Team Members

Ahmet Erdemir - study planning, assisting simulations, interpretation of results

Craig Bennetts - scripting for large scale analysis, execution of simulations, interpretation of results

Snehal Chokhandre - execution of simulations, interpretation of results

Progress

Source Code Repository

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

Data

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

Model Customization

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

Simulations

Post-Processing

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

Publications

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

References