Webinar ortho optimization 08 28 09 v1 - The ANSYS Experts Musculoskeletal... · 28-08-2009 · of the device (bending fatigue test, static torsion test, static four-point bend test)

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Musculoskeletal WebinarMusculoskeletal Simulation and Device

Design (webinar will start at 9am PST)

David Wagner, PhDOzen EngineeringAugust 28, 2009

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4D2%*,#%400BA%92%EA2The CAE Tools

Why Is Ozen Engineering Hosting Webinars?

- Get our name out there

- Another avenue that compliments dissemination throughpeer reviewed papers

- Resources available for research => would like to seesimilar dedication at the commercial level

- Improve collaboration between ‘people’ (researchers,students, teachers, companies) who use (or want to use)musculoskeletal simulation

- Answer the question: “What engineering problems can weaddress with the existing state of the art software andmethods currently available?”

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Summary

Optimization results and future questions

An example application (proximal radius fracture plate)

A Proposed workflow for incorporating musculoskeletal modeling

Modeling the human body – Musculoskeletal simulation of activitiesof daily living

Quick review of the previous webinar (uses of simulation)

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Uses of Simulation in the Orthopedic Industry

Replicating Physical Test Research (Internal/University)

Kim et al. 2008, SBC2008-193023

Li et al. 2008, SBC2008-192776

Design of Orthopedic Devices and ProstheticsASME Summer Bioengineering Conference (2008)

Finding out what went wrong

Finite-elementanalysis offailure of theCapital HipdesignsJanssen et al.2005

Benefits of Simulation

The use of computational simulation can be beneficial if it:• accurately represents and replicates the physics of the system• increases the number of possible design iterations (within a fixed

time)• decreases the cost associated with each design iteration• improves the fidelity of analysis as related to making design

decisions• is integrated in the design process

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Replicating Standardized Physical Tests

For example…ASTM F384 -06 Standard Specifications and Test Methods for Metallic Angled OrthopedicFracture Fixation Devices (no associated ISO standard)

• Methods for bending fatigue testing• Fatigue life over a range of maximum bending moment levels• Estimate the fatigue strength for a specified number of fatigue cycles• Not intended to define levels of performance of case-specific

ASTM F1264 Standard Specification and Test Methods for Intramedullary Fixation Devices• performance definitions• test methods and characteristics determined to be important to in-vivo performance

of the device (bending fatigue test, static torsion test, static four-point bend test)

• It is not the intention of this specification to define levels of performance or case-specific clinical performance of these devices, as insufficient knowledge to predictthe consequences of the use of any of these devices in individual patients forspecific activities of daily living is available

Components of a Device Analysis

Similar process flow used by Duda et al. 1998, Taylor M.E. et al. 1996, Speirs et al. 2007, TaylorR.E. et al. 2008, and Wagner et al. 2009

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From Kojic 2008

Comparison of Fracture Fixation Devices

Fixed PlateInternal compressionresulting from screw +fixation plate geometry

Intramedullary nailBending stiffness:Kb = ExI

E, Young’s Modulus of ElasticityI, the second moment of inertia

for bending of the nail crosssection

Torsional stiffness:Kt = ExIt

G, Shear ModulusIt, the second moment of inertia

for torsion

From Kojic 2008

Example Analysis - Fixed Plate Boundary Conditions

FixedConstraint

~ approximatingof axial loadduring humanwalking (singlestance phase of70 kgindividual)

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From Kojic 2008

Example Analysis Results - Effective Stresses

No slipconditionmodeledbetweenscrews, plate,and bone =>i.e. bondedcontacts

MPa

From Kojic 2008

Example Analysis Results - Fixed Plate Stresses

Stainless steelused for plateand screws

E = 2.1x105 Mpa

Poissons ratio = 0.3

Maximum effective stressless than critical values forstainless steel. However,cyclic loading leading tomaterial fatigue must alsobe considered

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From Kojic 2008

Example Analysis - Intramedullary Nail

Same bone geometry,material properties, and

boundary conditions as inthe neutralization plateanalysis

From Kojic 2008

Example Analysis - Intramedullary Nail StressesEffective stress concentrations in the nail near the screw regions => However, stress valuesare significantly lower than the corresponding neutralization plate regions (~80 MPa).Implication is that risk of intramedullary nail failure is significantly lower when compared toneutralization plate.

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From Kojic 2008

Example Analysis - Intracapsular Fractures

Parallel Screws Dynamic Hip Implant

Comparison of implant designs for internal fixation of intracapsular fractures of thefemoral neck

From Kojic 2008

Example Analysis - Parallel Screws BCs

Positive correlationbetweenintraoperativestability and

femoral neckfractures that havehealed (versus didnot heal),Rehnberg et al.1989

Fixed BoundaryCondition

FR: Pelvis to femur head reaction force, 199 daNFA: Force generated by gluteal muscles, 137 daNBody weight: 70 daN

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Summary






Can we usesimulation in amore ‘pro-active’way to developbetter products?

Doing More with Simulation (one idea)

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• Help understand what is going on inside the human body

• We use simulation for many other engineering analyses,why not for the human body as well

• Design/redesign ‘safe’ working environments

• Teaching

• Functional assessments (neuromusculoskeletal system)

• Create/Mimic realistic movement

• Sometimes the only way to understand and learn moreabout complex systems (like people!)

Simulation for !Biomechanics" - Why?

• Musculoskeletal Analysis– AnyBody– LifeModeler– Opensim/SIMM/SimTK– Madymo (TNO)– ESI Group– Marlbrook– Motek– Visual3D (c-motion)

• Digital Manikins– RAMSIS (Human

Solutions)– Jack (UGS/Siemens)– HumanBuilder/Delmia

(Dassault)– HumanCAD (NexGen)– SANTOS (U. Iowa)– Some others

• Motion Capture– BodyBuilder (Vicon)– Simi – Qualisys – SIMM (Motion Analysis)– XSENS– Many others

• CAE tools (FE/CAD)– ANSYS – LS-DYNA (ANSYS)– Abacus (Dassault)– AutoCAD (AutoDesk)– NASTRAN & ADAMS (MSC)– COMSOL

• Other tools– Matlab (Mathworks)– Mathematica

Simulation Software for !Biomechanics"

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The Holy Grail…

Task + Environment + Population

UniqueSimulation

from Parkinson and Reed (2008)

Working Within the Confines of the Current Technology

• Library of activities– Can’t rely (yet) on the musculoskeletal models to ‘adapt’ to new

task/environment conditions => particularly for novel (~non-cyclic)tasks

• Global Assessments vs. Better Products/Designs– Models that match measured results are great, but models that

exhibit realistic trends may be sufficient (and as useful)

• Better incorporation/understanding of variability– E.g. Within subject variability as indicator of model performance

• Will we ever be able to use Musculoskeletal Simulationwithout a corresponding validation study– Can’t ALWAYS be expected to conduct a validation study for a new activity– Must have confidence in the tools (e.g. Finite Element Models)

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Expanding the Use of Activities of Daily Living with a

Library of Musculoskeletal Simulations

• Long-term stability of hip-implants have been

evaluated using normalwalking, sit to stand, stairclimbing, and combinationsof those activities.

• Traditionally used aspass/fail tests to identifywhether a particular designperforms to a set ofminimum specifications

• Significantly Underutilized

Musculoskeletal Models Used Here80

14.6

35

5.2

549

121

709

782804

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121

121

(b)

Popular class of musculoskeletalmodels based on rigid bodydynamics:

• Bones and objects from theenvironment are rigid

• Muscles and ligaments aremass-less actuators

• Soft tissue – “wobbly“masses are not taken intoaccount (mass isconcentrated in bones)

• Phenomenological musclemodels

• ‘Easily’ scalable

Suited for simulating internal body forces (muscle,joint, ligament) for prescribed activities

Static 2D

Dynamic 3D (AnyBody

Modeling System)

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},..,1{ ,0

],[ where,

)()(

)()(

MMi nif !"

==MRfffdCf

MuscleforcesJoint

reactions

Internalforces

Appliedforces

The matrix C is rectangular. This means that there areinfinitely many solutions to the system of equations.How to pick the right one?

Formulating Dynamic Equilibrium

Using Optimization to Get a Solution

!

Minimize

G(f (M))

Subject to

Cf = d

fi(M )

" 0, i # {1,..,n(M )}

Objective function. Differentchoices give different muscle

recruitment patterns.

What should be used for ?

!

G(f(M))

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Musculoskeletal Models for Commercial Use

No ‘gold-standard’, just like with other pieces of engineeringsoftware

Commercially available (including open source) softwarepackages demand a knowledgeable user

Not traditionally incorporated in current design/engineeringmethodologies

Always room for improvement (I.e. improved validation, betteraccuracy, scaling to populations or patient specific, etc.)

Still must demonstrate where/how this arena of modeling canimprove specific processes (I.e. $$$)

Summary






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Bridging the Gap with Simulation

Physical Testing“Simulated”

Physical Testing“Simulated” In-

Vivo Performance

Implant Evaluation (see previous webcast for a more

substantive description of this process, 7-24-09)

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Implant Optimization

Summary






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Task: Wheel ChairPropulsionExertion

Device: TraumaImplant (proximalradius fracture)

Proposed Analysis

Necessary Pieces

Titanium alloy(Ti-6Al-4V)

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Titanium Alloy (Ti-6Al-4V)

Geometry Parameterization

A 100º angular plate position

(PlatePositionAngle) is

defined to be located on the

proximal lateral side of the

radius. An increase in the

angular position corresponds

to a counterclockwise rotation

of the plate about an axis

defined by looking down the

radius shaft from the proximal

toward the distal end.

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Design of Experiments (Parametric Exploration)

90 Designs, Full Factorial for:

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19043

14541

410039

35537

21035

Plate Depth (mm)Plate Position

(degrees)Plate Size (degrees)

30 Designs shown for 2mm Plate Depth =>

Design Parameter Boundaries

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Max Stress v. Plate Variables

Maximum Stress Calculation

Vs.

Top Surface Entire Plate

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Top Surface Equivalent Stress

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Plate Position (degrees)190

10045

35

2 mm Plate 3 mm Plate 4 mm Plate

707 MPa

106 MPa

612 MPa

58 MPa

542 MPa

37 MPa

Plate Size (degrees)

Data available for Fatigue Life, Max Principal Strain, Max Displacement, etc.=> criteria a design engineer could use to make develop better products

Summary






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Optimization Flow (Desired)

- Minimize Maximum Stress in Plate- Minimize Maximum Displacement in Plate- Minimize Plate Mass

- Plate Orientation

wrt bone- Plate Thickness- Plate Size (angular)

Optimization Flow

- Minimize Maximum Stress in Plate- Minimize Maximum Displacement in Plate- Minimize Plate Mass

- Plate Orientation

wrt bone- Plate Thickness- Plate Size (angular)

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Optimization Performed in ModeFRONTIER

250 design runs~8 minutes per run (34 hour total run time)MOGA-II optimization algorithm

Multi Objective GeneticAlgorithm - an efficient multi-

objective genetic algorithm(MOGA) that uses a smart multi-search elitism. This new elitismoperator is able to preservesome excellent solutions withoutbringing premature convergenceto local-optimal frontiers

Results - Input - Plate Position Angle

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Results - Input - Plate Size Angle

Results - Input - Plate Thickness

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Scatter Plot of Design Points

Plot to stare at…

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Parallel Coordinate Charts (another way to sift through the data)

Parallel Coordinate Charts (another way to sift through the data)

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Another Optimization Run

80 degrees

Trade Off Between Mass and Plate Stress

Pareto Designs Marked

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Only Pareto Points Plotted

More Possibilities…Robust Design => ApplyingUncertainty to Parameters

OR…SensitivityAnalysis to determinerelationship betweenvariation inparameters andoutcome metrics

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Contacting Ozen to Learn More

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Documents

Webinar ortho optimization 08 28 09 v1 - The ANSYS Experts Musculoskeletal... · 28-08-2009 · of the device (bending fatigue test, static torsion test, static four-point bend test)