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Contents

  1. Synopsis
    1. Use Case
    2. Simulation Aims
    3. Model
    4. Inputs
    5. Outputs
    6. Simulation Conditions
  2. Use Cases
    1. max_retries & max_refs
    2. flexion angle & Anterior-Posterior (AP) force
      1. SET 1
      2. SET 2
    3. flexion angle & Internal-External (IE) torque
      1. SET 1
      2. SET 2
    4. flexion angle & Varus-Valgus (VV) torque
      1. SET 1
      2. SET 2
    5. SPRING SETS, 90 degree passive flexion, 1.0 s, ramp-only
      1. NO SPRING SETS
      2. Transverse Ligament
        1. 33.3 N/mm / spring
        2. 66.6 N/mm / spring
        3. 100 N/mm / spring
      3. Medial Ligament
        1. 33.3 N/mm / spring
        2. 66.6 N/mm / spring
        3. 100 N/mm / spring
      4. Joint Capsule
        1. 33.3 N/mm / spring
        2. 66.6 N/mm / spring
        3. 100 N/mm / spring
    6. SPRING SETS, 45 degree passive flexion, 1.0 s, ramp-only
    7. SPRING SETS, 90 degree passive flexion, 2.0 s, ramp-only
  3. Team Members
  4. Progress
    1. Source Code Repository
    2. Data
    3. Model Customization
    4. Simulations
    5. Post-Processing
    6. Publications
  5. References

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

  • To understand the role of joint loading on convergence characteristics
  • To understand the role of simulation (numerical analysis) parameters on convergence characteristics
  • To understand model parameters on convergence characteristics
  • To understand new model features on convergence characteristics

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):

  • flexion
  • internal/external rotation torque
  • varus/valgus torque
  • anterior/posterior force
  • medial/lateral force
  • compression/distraction force

Outputs

  • Convergence metrics (primary)
    • Completion of simulation (Yes/No)
    • If not completed - time point at which the simulation crashed
    • If completed - computation time (also provide computer specifications), number of iterations
  • Time histories of kinematics-kinetics of the tibiofemoral joint (six degrees of freedom) (secondary)
    • flexion torque
    • internal/external rotation
    • varus/valgus
    • anterior/posterior translation
    • medial/lateral translation
    • compression/distraction
  • Post-processed joint mechanics information (secondary)
    • Comparison of tibia kinetics and femur kinetics
    • Comparison of tibiofemoral joint kinematics to baseline simulation results
  • Time histories of stress-strain behavior (secondary)

Simulation Conditions

  • Simulation (numerical analysis) parameters (refer to FEBio manual for descriptions):
    • Convergence tolerances
      • dtol
      • etol
      • rtol
      • lstol
    • Time stepper properties
      • dtmin
      • dtmax
      • max_retries
      • opt_iter
      • aggressiveness
    • Newton/quasi-Newton parameters
      • max_refs
      • max_ups
    • cmax
    • min_residual
    • Analysis type (static/dynamic)
  • Model parameters
    • Increase of menisci circumferential modulus
    • Increase of cartilage modulus (relative to menisci)
    • Increase of ligament fiber moduli
    • Change in tibia and femur inertial properties (for dynamic simulations)
  • Model changes
  • Loading conditions
    • passive flexion
    • internal/external rotation laxity
    • anterior-posterior translation laxity
    • varus/valgus laxity
    • pivot shift

Use Cases

max_retries & max_refs

Parameter permutations:

  • max_retries = 5,10,20
  • max_refs = 5,10,20

Converged:

  • all permutations

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:

  • flexion angle = 0,30,60,90 degrees
  • AP force = -100 (P), 100 (A) N
  • max_retries = 5
  • max_refs = 20

Converged:

  • flexion angle = 0 degrees
  • AP force = -100 (P) N

Non-converged:

  • all other permutations

  • failed due to: Max. nr of retries reached.

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

SET 2

Parameter permutations:

  • flexion angle = 0,30,60,90 degrees
  • AP force = -100 (P), 100 (A) N
  • max_retries = 20
  • max_refs = 20

Converged:

  • flexion angle = 0,30 degrees
  • AP force = -100 (P) N

Non-converged:

  • all other permutations
  • flexion angle = 60 degrees completed flexion
  • flexion angle = 90 degrees did not complete flexion

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

flexion angle & Internal-External (IE) torque

SET 1

Parameter permutations:

  • flexion angle = 0,30,60,90 degrees
  • IE torque = -5 (I), 5 (E) N*mm = -0.005,0.005 N*m
  • max_retries = 5
  • max_refs = 20

Converged:

  • flexion angle = 0,30 degrees
  • IE torque = -5,5 N*mm

Nonconverged

  • flexion angle = 60,90 degrees
  • IE torque = -5,5 N*mm

  • failed due to: Max. nr of retries reached.

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

SET 2

Parameter permutations:

  • flexion angle = 0,30,60,90 degrees
  • IE torque = -5000 (I), 5000 (E) N*mm = -5,5 N*m
  • max_retries = 5
  • max_refs = 20

Nonconverged:

  • all permutations
  • flexion angle = 0,30 degrees, completed flexion, began applying loading
  • flexion angle = 60,90 degrees, didn't complete flexion

  • failed due to: Max. nr of retries reached.

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

flexion angle & Varus-Valgus (VV) torque

SET 1

Parameter permutations:

  • flexion angle = 0,30,60,90 degrees
  • VV torque = -10 (Varus), 10 (Valgus) N*mm = -0.01,0.01 N*m
  • max_retries = 5
  • max_refs = 20

Converged:

  • flexion angle = 0,30 degrees
  • VV torque = -10,10 N*mm

Nonconverged:

  • flexion angle = 60,90 degrees
  • VV torque = -10,10 N*mm

  • failed due to: Max. nr of retries reached.

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

SET 2

Parameter permutations:

  • flexion angle = 0,30,60,90 degrees
  • VV torque = -10000 (Varus), 10000 (Valgus) N*mm = -10,10 N*m
  • max_retries = 5
  • max_refs = 20

Converged:

  • flexion angle = 0 degrees
  • VV torque = -10000,10000 N*mm

Nonconverged:

  • flexion angle = 30,60,90 degrees
  • VV torque = -10000,10000 N*mm
  • flexion angle = 30,60 degrees, began loading
  • flexion angle = 90 degrees, didn't finish flexion

  • failed due to: Max. nr of retries reached.

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:

no_springs_flexion_90.png

Transverse Ligament

33.3 N/mm / spring

transverse_33.3_flexion_90.png

66.6 N/mm / spring

transverse_66.6_flexion_90.png

100 N/mm / spring

transverse_100_flexion_90.png

Medial Ligament

33.3 N/mm / spring

medial_33.3_flexion_90.png

66.6 N/mm / spring

medial_66.6_flexion_90.png

100 N/mm / spring

medial_100_flexion_90.png

Joint Capsule

33.3 N/mm / spring

capsule_33.3_flexion_90.png

66.6 N/mm / spring

capsule_66.6_flexion_90.png

100 N/mm / spring

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

Cases/ConvergenceOptimization (last edited 2016-05-04 22:09:52 by localhost)