aks documentation

7/21/2019 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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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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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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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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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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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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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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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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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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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


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


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).

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