current concepts and open problems in computational
TRANSCRIPT
ANSYS/CADFEM Users‘ Meeting Dresden 2007
Current Concepts and Open Problems Current Concepts and Open Problems in Computational Clinical Biomechanicsin Computational Clinical Biomechanics
Institut für UnfallchirurgischeForschung und Biomechanik
www.biomechanics.de
Ulmer Zentrum für Wissenschaftliches Rechnen
www.uzwr.de
U. Simon, T. Wehner, D. Nolte, F. Niemeyer, L. Claes
Introduction: Clinical Problems ...Introduction: Clinical Problems ...
...where computers might help:...where computers might help:
ImplantsImplants•• Function (strength, elasticity, joint kinematics, ...)Function (strength, elasticity, joint kinematics, ...)•• Loading (muscle forces)Loading (muscle forces)•• Biocompatibility (contact, wear, elasticity, ...)Biocompatibility (contact, wear, elasticity, ...)•• Adaptation of adjacent tissues (stress shielding)Adaptation of adjacent tissues (stress shielding)
OsteoporosisOsteoporosis•• Misalignment between formation and loss of boneMisalignment between formation and loss of bone•• Diagnosis: fracture risk from CT imagesDiagnosis: fracture risk from CT images
Fracture HealingFracture Healing•• Minimizing healing timeMinimizing healing time•• Preventing ComplicationsPreventing Complications
Back PainBack Pain•• Intervertebral disk degeneration (disk prolapse)Intervertebral disk degeneration (disk prolapse)•• Optimizing treatment and implantsOptimizing treatment and implants
ContentsContents
1 Structural Mechanics / Material Properties1 Structural Mechanics / Material Properties
2 Musculoskeletal Loads2 Musculoskeletal Loads
3 Fracture Healing / Remodeling3 Fracture Healing / Remodeling
1 Structural Mechanics / Material Properties
ISObone screw
Local DamageLocal Damage
Organ Level Tissue Level
L0
3-Point Bendingof a
bone specimen
Tensile Testof a
standardized Specimen
Multiscale Problem
Cell Level
Atomic
Force Microscopyof a
living cell
Yamada 1970; Hori & Lewis 1982; Davy & Connolly 1982; Proctor et al. 1989; Mente & Lewis 1994; Rho et al. 1995; Augat et al. 1998; Tanck et al. 1999
HaematomaGranulation tissue 0,01 ... 3 MPaFibrous tissueCartilage 0,4 … 500 MPaWoven bone 400 … 6000 MPa Cortical bone 10 ... 20 GPa
Material Properties
More complex Laws:•
Nonlinear
•
Hyperelastic
(nonlinear elastic + large deformations)
•
Viscoelastic
•
Non-elastic, plastic, yielding, hardening
•
Anisotropic
•
Fatigue, recovery
•
Remodeling, healing
Simplest Material Law:•
Linear-elastic, isotropic (Hook’s Law)
Biological Tissues know all of these bad things!Biological Tissues know all of these bad things!
Material Properties
Structural Mechanics Structural Mechanics cu
rren
t con
cept
s
open
pro
blem
s
Complex GeometryComplex Geometry•• CT2FECT2FE
•• Friction: Not constant!Friction: Not constant!•• Coagulation, Coagulation, IngrowthIngrowth
ContactContact•• Surface reconstructionSurface reconstruction
Complex Material PropsComplex Material Props•• MultiscaleMultiscale•• NonNon--linear, ..., nonlinear, ..., non--everything!everything!•• ... at the same time... at the same time
www.anybodytech.com
MusculoMusculo--skeletal modelskeletal model
Muscle forces,Muscle forces,internal loadsinternal loads
•• Inverse dynamicsInverse dynamics
•• OptimizationOptimization
MeasuredMeasuredmovementmovement
2 Musculoskeletal Loads2 Musculoskeletal Loads
Example: Rat GaitExample: Rat Gait
UFBSIM
Erik ForsterUwe Wolfram
Musculoskeletal Loading Musculoskeletal Loading cu
rren
t con
cept
s
open
pro
blem
sModeling Modeling •• Anatomy (bones, joints, muscles)Anatomy (bones, joints, muscles)•• AnybodyAnybody
MethodsMethods•• Inverse DynamicsInverse Dynamics•• Optimization (min. effort, energy)Optimization (min. effort, energy)
•• How to account for coHow to account for co-- contraction?contraction?
•• ... for pain?... for pain?
Fracture HealingFracture Healing
Clinical Relevance:Clinical Relevance:• 5-10% Complications
Aims:Aims:• Minimize healing time• Avoid Complications• Optimize implants
Callus Healing ProcessCallus Healing Process
Problem:Problem:New bone formation only
with low strain state !
Biological Solution:Biological Solution:1.Callus: larger diameter2.Via cartilage to bone
Method: Iterative SimulationMethod: Iterative Simulation
Spalt
Fuzzy rules:• Bone formation• Cartilage formation• Revascularization
Fuzzy rules:• Bone formation• Cartilage formation• RevascularizationResult
Simulation over timeResult
Simulation over time
Fuzzy LogicBiological processesFuzzy Logic
Biological processes
Initial stateGeometry, Mesh, Loads, BC
Initial stateGeometry, Mesh, Loads, BC
FEAStrain field
FEAStrain field
Fuzzy Logic ControllerFuzzy Logic Controller
FuzzyFuzzyControllerController
StrainStrain
Blood supplyBlood supply
Change of tissue Change of tissue typetype
FuzzyficationFuzzyfication::
0
0,5
1
0,0001 0,001 0,01 0,1 1
Strain, local
Mem
bers
hip
Fuzz
yFu
zzy --
ficat
ion
ficat
ion
Defu
zzy
Defu
zzy --
ficat
ion
ficat
ion
niedrig mittel hoch zerstörerisch
Fuzzy rules:Fuzzy rules:
If …strain is low and blood supply is good, …then …bone concentration is increasing.
Case BCase BLarge initial movement 1.25 mm
Case ACase ASmall initial movement 0.25 mm
Day35
DayDay3535
ResultsResults
Blood Bone Cartilage Blood Bone Cartilage
Case BCase BLarge initial movement 1.25 mm
Case ACase ASmall initial movement 0.25 mm
Validation with experimental results (sheep)Validation with experimental results (sheep)
0.00
0.25
0.50
0.75
1.00
1.25
1.50
0 7 14 21 28 35 42 49 56Healing days
IFM
in m
m
1032104410571100FE
0.00
0.25
0.50
0.75
1.00
1.25
1.50
0 7 14 21 28 35 42 49 56Healing days
IFM
in m
m
1030105410631129FE
Fracture Healing / Remodeling Fracture Healing / Remodeling cu
rren
t con
cept
s
open
pro
blem
sMethodsMethods•• Simulation of dynamic systemsSimulation of dynamic systems•• ... adaptive systems... adaptive systems
Including biological factorsIncluding biological factors•• TGF, BMP, ......................TGF, BMP, ......................
CPU timeCPU time•• Geometry, NonlinearitiesGeometry, Nonlinearities•• Automatic optimizationAutomatic optimization
•• Methods are quit improvedMethods are quit improved
•• Open problems: biological factors, loadsOpen problems: biological factors, loads
•• ValidationValidation
•• Necessary: Interdisciplinary teamNecessary: Interdisciplinary team
clinicians, biologists, engineers, mathematicians, IT specialistclinicians, biologists, engineers, mathematicians, IT specialistss
SummarySummary
Institut für UnfallchirurgischeForschung und Biomechanik
www.biomechanics.de
Ulmer Zentrum für Wissenschaftliches Rechnen
www.uzwr.de