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Application of a Calibration Method Provides More Realistic Results for a Finite Element Model of a Lumbar Spinal Segment

Hendrik SchmidtFrank Heuer Lutz ClaesHans-Joachim Wilke

Institute of Orthopaedic Research and Biomechanics,Center of Musculos-Skeletal Research (zmfu),University of Ulm

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Aim: Validation of a finite element model of a single spinal motion segment

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CT 3D

Philips MX 8000IPT® amira® 3.0

Determination of the geometry of bony structures

Determination of the geometry of soft tissue

macroscopical frozen cutsMRI-Slices

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L4

L5

8 Fiber Layers

Nucleus Pulposus

Cartilaginous Endplate

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Car

tilag

e

Annulus

Nucleus

Spo

ngio

sa

Cor

tex

Fibe

rs

100 Pa 1 kPa 10 kPa 100 kPa 1 MPa 10 MPa 100 MPa 1 GPa 10 GPa 100 GPa

Elasticity

Material properties of different biological structures

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moment

angl

e

Validation parameter

Range of Motion

RoM

RoM

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Material modification

ROM

Often performed validation procedures

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Angle in °

Intact

Bilateral Hemifacetectomy

Nucleotomy

w/o SSL & ISL

1086420

In-vitro Data FEMMin / Max Values

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Marco Viceconti, Clinical Biomech, 2005

“I have a question and I am sure you don‘ t like it:

How did you validate your finite element model?”M. Viceconti, S. Olsen, L. Nolte, K. Burton

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In-vitro Studies

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Intact

w/o SSLw/o ISLw/o FLw/o FC

w/o VA

w/o PLLw/o ALL

w/o Nucl

Load application

Flexion

Extension

Lateral bending

Axial rotation

Load magnitudes

1, 2.5, 5, 7.5, 10 Nm

∑= 180

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Calibrationof the

Finite Element Model

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Nucleus

FL

SSLISL

L4

L5

ALLPLL

FC

VA

Nucleus

FL

SSLISL

L4

L5

ALLPLL

FC

VA

Annulus

with ALL with PLL

with VA

with FCwith FLwith ISL

Intact

Load application

Flexion

Extension

Lateral bending

Axial rotation

Load magnitudes

1, 2.5, 5, 7.5, 10 Nm

∑= 180

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0.3 0.5 0.8 1.0 1.3 1.5 1.8 2.0

10.0 Nm 7.5 Nm 5.0 Nm 2.5 Nm

Ground substance Fibers

Annulus fibrosus

Flexion10.0 Nm 7.5 Nm 5.0 Nm 2.5 Nm

Stiffness coefficient k

You

ng’s

mod

ulus

of

grou

nd-s

ubst

ance

in M

Pa

0.6

1.0

1.4

1.8

2.0

0.3 0.5 0.8 1.0 1.3 1.5 1.8 2.0

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Annulus with NUC with ALLwith PLL with VA with FLwith ISL with SSL (INTACT)

Ran

ge o

f Mot

ion

in °

0

5

10

15

20

Applied Moment in Nm2.5 5.0 7.5 10.0

Range of Motion in Flexion

FEM Min/Max in-vitro data

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Accuracy of the calibrated FE-model

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Angle in °

Intact

Bilateral Hemifacetectomy

Nucleotomy

w/o SSL & ISL

1086420

In-vitro Data FEMMin / Max Values

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Conclusion

•Only the calibrated FE-model showed a good agreement to all defect situations

but

•The current model is only suitable for quasi-static load application

Validation is “a never ending” process!!!

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Thank you for your Attention!Thank you for your Attention!