AKS Documentation
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Transcript of AKS Documentation
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Abaqus Knee Simulator
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Table of Content
Introduction
Installation and conventions
Knee parts
Test suites
Workflows
Appendix
References
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What is the knee simulator?
Abaqus Knee Simulator (AKS) is an automatedmodeling tool for building
advancedknee implant simulations based on a validatedframework
Abaqus Knee Simulator includes five workflowswhich cover various aspects
of knee implant design evaluation:
Contact mechanics
Implant constraint
TibioFemoral (TF) constraint
Wear simulator
Basic Total Knee Replacement (TKR) loading
Introduction
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Introduction
Step by Step Import geometries
Build test suite
Set-up each workflow
Check for interference
Adjust positioning
Define output requests
Set simulation options
Run analysis and monitor
progress
Visualize results
Import
partsCreate
test suite Check for
interference
Adjust
positioning
Define output
requests
Set simulation
options
Run analysis and
monitor progress
Visualize
results
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GUI Overview
AKS panel includes the Knee Partstab and the Test Suites tab
Introduction
AKS panel
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Knee implant components are imported into AKS using
the Knee Partstab
Test suites which are repositories of workflows are
created using the Test Suites tab
Introduction
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Designerand Analystmodes
The simulator has two interface modes
The designer mode provides a streamlined interface for performing knee
implant simulation
The analyst mode extends the designer mode by providing full accesses to
features of Abaqus/CAE
Introduction
Designer mode Analyst mode
Switches between the two modes
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For both modes, everything you need to build a simulation is
collected in a single panel where you specify
output requests
simulation options
result visualization options
Introduction
Output request Simulation options Result visualization
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Here are the steps:
1. Install Abaqus/CAE on Windows
platform
2. Install license file with Abaqus Knee
Simulator feature enabled
3. Open command line window
4. Enter: abaqus kneeapp
Installation and Conventions
Installation and execution
Abaqus Knee Simulator comes with
all Abaqus/CAE installation on
Windows platform
Special license is required to enable
AKS
Enter the following command in a
command line window to start
Abaqus Knee Simulator
abaqus kneeapp
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Platform
AKS GUI is only supported for Window platform including win32 and win64
The analysis generated by AKS can be solved using other platforms
supported by Abaqus/Explicit except for the wear simulator which requires
compiled user subroutine library for the specific platform
Please contact our local office for the l ibrary file
Unit system
As AKS provides a set of human knee geometry and material properties, itrequires user input and geometries to use the same consistent unit system:
length: mm | force: N | pressure: MPa
Installation and Conventions
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Sources of implant geometries
From neutral geometry files exported
from CAD
SAT, IGES, STEP, etc.
From associative CAD interfaces
Pro/E, SolidWorks, CATIA V5, NX
Note the associative interface license need to be acquired separately
From existing CAE model
The user can copy existing CAE parts into the KneeSim-Parts model to be used by
AKS
Knee Parts
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Knee type
The knee anatomy (bones, soft tissues)
provided in the simulator belongs to a right
knee
The user can import either right knee or a leftknee implants
If left knee implants are imported, they will be
mirrored to right knee implants to be consistent
with the anatomy
Knee Parts
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Implant geometry landmarks
Femur component
A plane parallel to the frontal plane of the body
Dwell (lowest) point for medial and lateral condyle
surface
Knee Parts
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Implant geometry landmarks
Tibia component
A plane parallel to the transverse plane of
the body
Dwell (lowest) point for medial and lateral
condyle surface
Knee Parts
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Implant geometry landmarks
Patella component
A plane parallel to the frontal plane
A point on the medial side
A point on the posterior side
Knee Parts
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Dwell points
If a mistake is made to the dwell point, you have
the option to either edit or swap the dwell points
by right-mouse-click on the imported part
Sets and surfaces
Sets and surfaces can also be created for output
purposes
Sets and surfaces created in Knee Parts tab will
be available to all test suites created afterwards
Knee Parts
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Meshing
The femur and patellar button components are mesh automatically upon
import
Femur component as rigid triangle elements
Patellar button as 2nd
order tetrahedron elements
The parts are seeded with a default element size calculated based on the
geometry landmarks
Knee Parts
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Meshing
Two elliptical partitions with user-specified major and minor radii of the
ellipses are created on the tibial insert to provide automated hexahedral
mesh for the area in contact with the femur component
Knee Parts
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Here are the steps:
1. Single click on Add Test Suite
2. Give a suite name
3. Select parts to be included in the test
suite
4. Select material model for each part
5. Select workflows
6. Select modeling space (only
applicable for TF constraint and basic
TKR loading workflows
7. Select bundle type (only applicable forbasic TKR loading workflow
Test Suites
Build a test suite
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Here are the steps:
1. Right-mouse-click on the workflow to
access inference check
2. Surfaces with interference will be
highlighted
3. Right-mouse-click on Parts to accesspositioning options
4. Repeat step 1-3 until there is no
interference between the parts
Note: interference between anatomy and
implants can be ignored
Test Suites
Set up workflows
Remove interference between
implant parts
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Here are the steps:
1. Select sets for outputs
a. Sets can be created on-the-fly
2. Select surfaces for outputs
a. Surfaces can be created on-
the-fly
3. Pick output variables
a. Specific sets/surfaces can be
selected
The variables may be different from oneworkflow to another
Test Suites
Set up workflows
Set output request
T S i
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Here are the steps:
1. Choose deformable or rigid insert
a. Rigid insert could be used for
kinematic and contact forcesevaluation with significant
computational savings and little
compromise on accuracy
2. Select platform type
3. Input joint load
4. Enter knee flexion angle
5. Set workflow-specific options which is
discussed in details later on
6. Set job submission options, write
input and submit job
Test Suites
Set up workflows
Set simulation options
T t S it
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Here are the steps:
1. Retrieve AKS results
2. Select results variable to be visualized
3. Select location of the variable
4. Choose X axis quantity to be time or
flexion angle
5. Select analysis step
6. Pick specific flexion angel
7. Visualize with various options
Note: Results output as a function of flexion
angle need to be exported as a text f ile
and graphically visualized externally
Test Suites
Set up workflows
Visualize results
W kfl
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Contact mechanics workflow
Objective:predict contact mechanics and
stresses of the components under basic
loading conditions, and facilitate comparison
of devices
A constantor varyingcompressive load is
applied to the femoral component, with a
prescribed medial-lateral load distribution,
to bring the implants into contact
Workflows
W kfl
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Contact mechanics workflow
The femoral component is flexedto a prescribed
flexion angle, with choices of fixedor freedegrees-of-
freedom for medial-lateral (M-L) translation, internal-
external (I-E) rotation and varus-valgus (V-V) rotation
Contact area, peak and average contact pressure, and
stress in the components are reported throughout the
simulation
Workflows
Workflows
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Implant constraints workflow
Objective:Evaluate the laxity for a set of femoral and
tibial components without surrounding soft tissue
structures
Anterior-posterior (A-P) displacement, internal-external
(I-E) rotation and medial-lateral (M-L) displacement
tests available
Workflows
Workflows
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Implant constraints workflow
For a given test
a displacement or rotation is applied in both directions
under a prescribed compressive load
with fixed or free options for the remaining degrees-of-
freedom
the force or torque generated on the insert is measured
Workflows
Workflows
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Implant constraints workflow
The tests may be preformed at a series of flexion angles
Kinematic, force, contact mechanics and stress data is
produced from each test
Workflows
Workflows
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Tibiofemoral (TF) constraints workflow
Objective: describe the laxity of the
tibiofemoral joint, with physiological
ligamentous constraint, for a specific implant
design
The workflow includes femur and tibia bones,
femoral and tibial components, plus 1-D or 2-
D representation of the primary ligaments
crossing the tibiofemoral joint
Workflows
Workflows
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Tibiofemoral (TF) constraints workflow
Ligaments can be selectively included or omitted
from the analysis
to represent situations such as a posterior-stabilized
implant (no posterior cruciate ligament)
or to represent tibiofemoral joint with torn or weak
ligaments
Workflows
Workflows
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Tibiofemoral (TF) constraints workflow
A compressive load is applied and a series of
laxity tests (A-P, I-E and V-V), performed at
prescribed flexion angles, are available
For each test, a load (an A-P force, I-E torque or
V-V torque) is applied to the joint, with remaining
degrees-of-freedom selected as either fixed or
free
Workflows
Workflows
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Tibiofemoral (TF) constraints workflow
Ligament mechanical properties (initial tension,
linear stiffness) can be adjusted to evaluate the
influence of variability in ligament properties, or
to recreate specimen-specific data
Location of femur, tibia and their associated
ligament attachment sites can be shifted
Six-degree-of-freedom kinematics, ligament
forces, insert forces, stresses and contactmechanics are available as outputs
Workflows
Workflows
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Wear simulator workflow
Objective: predict wear (wear volume, maximum linear
wear depth, and average linear wear) over a
prescribed number of cycles
Femoral and tibial components only (no bone or soft-
tissue) are included in the analysis
Mechanical restraint is provided in the anterior and
posterior directions to simulate behavior of the
cruciate ligaments
Workflows
Workflows
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Wear simulator workflow
A typical gait cycle, taken from ISO standards,
including flexion profile, compressive load, A-P
force and I-E torque is simulated
LinearArchardsLaw or Cross-shear wear
algorithms may be selected to predict wear on the
insert
Workflows
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Basic total knee replacement (TKR) loading
workflow
Objective: evaluate tibiofemoral and
patellofemoral kinematics, contact mechanics,
component stress, ligament and muscle forces
under physiological loading conditions for a
variety of activities of daily living
In addition to femoral and tibial bones and
components, and 1-D and 2-D soft-tissue
representation, the extensor mechanism (patella
bone, patellar implant, patellar tendon and
quadriceps) is also represented in the model
Workflows
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Basic total knee replacement (TKR) loading
workflow
The quadriceps could be either represented as
a single bundle, or as multiple bundles,
including medial and lateral longus and
oblique structures
A variety of activities (gait, squat, chair-rise,
stepdown) may be simulated, with loading
profiles dependent on the choice of activity
Workflows
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Basic total knee replacement (TKR) loading
workflow
A (activity-dependent) flexion profile is applied
to the femur, while quadriceps force is
distributed among the quadriceps bundles
Appendix
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Abbreviation Full Name
LCL Lateral Collateral Ligament
SMCL Medial Collateral Ligament
ALS Anterior Lateral Structure
PFL Popliteofibular ligament
OPL Oblique popliteal ligament
PCL Posterior Cruciate Ligament
PCAPL Lateral Posterior Capsule
PCAPM Medial Posterior Capsule
Table 1. Reference for Cut Ligaments Abbreviation
Abbreviation Full Name
LCLA_SP Anterior Lateral Collateral Ligament
LCLM_SP Medial Lateral Collateral Ligament
LCLP_SP Posterior Lateral Collateral Ligament
SMCLA_SP Anterior Medial Collateral Ligament
SMCLM_SP Medial Medial Collateral Ligament
SMCLP_SP Posterior Medial Collateral Ligament
ALS_SP Anterior Lateral Structure
PFL_SP Popliteofibular ligament
OPL_SP Oblique popliteal ligament
alPCL_SP Posterior Cruciate Ligament
pmPCL_SP Postero-medial Posterior Cruciate Ligament
Table 2. Reference for Ligament Properties Abbreviation
Abbreviation Full Name
FIBER_PL Patella Ligament
FIBER_RF Rectus Femoris
FIBER_VASTI Vasti
Table 3. Reference for Muscle Properties Abbreviation
References
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The workflows options and corresponding tissue material properties
are based on the following publications
Mark A. Baldwin, Chadd W. Clary, Clare K. Fitzpatrick, James S. Deacy, Lorin P. Maletsky,
Paul J. Rullkoetter, Dynamic finite element knee simulation for evaluation of knee
replacement mechanics, Journal of Biomechanics, Volume 45, Issue 3, 2 February 2012,
Pages 474-483
Lucy A. Knight, Saikat Pal, John C. Coleman, Fred Bronson, Hani Haider, Danny L. Levine,
Mark Taylor, Paul J. Rullkoetter, Comparison of long-term numerical and experimental total
knee replacement wear during simulated gait loading, Journal of Biomechanics, Volume 40,Issue 7, 2007, Pages 1550-1558
Mark A. Baldwin, Chadd Clary, Lorin P. Maletsky, Paul J. Rullkoetter, Verification of predicted
specimen-specific natural and implanted patellofemoral kinematics during simulated deep
knee bend, Journal of Biomechanics, Volume 42, Issue 14, 16 October 2009, Pages 2341 -
2348
Jason P. Halloran, Anthony J. Petrella, Paul J. Rullkoetter, Explicit finite element modeling oftotal knee replacement mechanics, Journal of Biomechanics, Volume 38, Issue 2, February
2005, Pages 323-331
References
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Fitzpatrick CK, Baldwin MA, Ali AA, Laz PJ, Rullkoetter PJ. Comparison of patellar bone
strain in the natural and implanted knee during simulated deep flexion. J Orthop Res. 2011
Feb;29(2):232-9
Jason P. Halloran, Sarah K. Easley, Anthony J. Petrella, and Paul J. Rullkoetter, Comparison
of Deformable and Elastic Foundation Finite Element Simulations for Predicting Knee
Replacement Mechanics, J. Biomech. Eng. 127, 813 (2005)
Petrella, AJ, Armstrong, JR, Laz, PJ, Rullkoetter, PJ, A novel cross-shear metric for
application in computer simulation of ultra-high molecular weight polyethylene wear,
Computer Methods in Biomechanics and Biomedical Engineering, (in press).