Vara Isvilanonda Specific Aim 4: Introduction Objective To develop - - PowerPoint PPT Presentation

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Vara Isvilanonda Specific Aim 4: Introduction Objective To develop - - PowerPoint PPT Presentation

Jan 01, 2023 527 likes •1.02k views

Vara Isvilanonda Specific Aim 4: Introduction Objective To develop and validate two subject-specific FE foot models (normal and diabetic), to explore the plantar pressure and internal soft tissue stress during quiet stance and the stance phase

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Vara Isvilanonda

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Objective

To develop and validate two subject-specific FE foot models (normal and diabetic), to explore the plantar pressure and internal soft tissue stress during quiet stance and the stance phase of gait, and to investigate the effect of soft tissue assumptions.

Specific Aim 4: Introduction

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Normal and diabetic subjects

! Normal subject

" Age

43 year-old (male)

" Body weight

945 N

! Diabetic subject

" Age

31 year-old (male)

" Body weight

688 N

" Duration of diabetes

> 25 years

Specific Aim 4: Introduction

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FE foot model development

Obtain imaging data

CT (10% BW per foot) MRI (unloaded)

Bone anatomy Skin, fat and muscle anatomy

Specific Aim 4: Method

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Segmentation

L A P L M A P S I S I

Specific Aim 4: Method

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Boolean operations

Generate joint cavities Generate skin thickness Smoothen surfaces Eliminate gaps/overlaps

Specific Aim 4: Method

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FE model pre-processing

! Mesh with tetrahedral elements ! Element size (2.5mm), type

(ELFORM13) determined from mesh convergence analysis

! Bone-soft tissue share nodes Specific Aim 4: Method

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Material properties

! Materials: rigid bone, Ogden hyperelastic soft tissue

" (µs, αs), (µF, αF) and (µM, αM) are subject-specific skin, fat and

muscle material properties determined in vivo (Specific Aim 2)

" Dorsal soft tissue modeled with subject-specific generic soft tissue

(µG, αG)

( )

( )

( )

2 3 2 1 3 2 1

1 2 1 3 ~ ~ ~ , , − + − + + = J K W

α α α

λ λ λ α µ λ λ λ

3 1

~ J

i i

λ λ =

Specific Aim 4: Method

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Ligament

! 102 non-linear, tension only ligaments Specific Aim 4: Method

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Tendon

! 9 extrinsic muscle tendons (seatbelts – slip rings) Specific Aim 4: Method

9Tendons are:

  • Achilles
  • Tibialis anterior
  • Tibialis posterior
  • Peroneus longus
  • Peroneus brevis
  • Extensor hallucis longus
  • Externso digitorum longus
  • Flexor hallucis longus
  • Flexor digitorum longus
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Tendon

! 9 extrinsic muscle tendons (seatbelts – slip rings) Specific Aim 4: Method

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Plantar fascia

! Material properties in 4 regions from

cadaveric tests from 3rd Specific Aim

Medial Middle distal Lateral Middle proximal Specific Aim 4: Method

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Foot model of the normal subject Foot model of the diabetic subject

Specific Aim 4: Method

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Experimental Validation

3 validation conditions

! Quasi static: Passive 10% BW foot compression ! Quasi static: Quiet stance ! Dynamic: Stance phase of gait Specific Aim 4: Method

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Validation 1: passive compression

! Bony alignments from 10% BW CT data are compared to

simulation

Specific Aim 4: Method – Validation1

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Validation 1: passive compression

! Bony alignments from 10% BW CT data are compared to

simulation

Cavanagh et al., 1997

Specific Aim 4: Method – Validation1

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Passive compression FE simulation

Fixed ground

Specific Aim 4: Method – Validation1

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Passive compression FE simulation

In vivo CT data FE simulated data

Specific Aim 4: Method – Validation1

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Passive compression validation results

10 20 30 40 50 60 70 80 Angle (deg)

Normal foot model

Experimental data Simulated data (zero Achilles force) Simulated data (20% bw Achilles force [near heel lift]) Specific Aim 4: Results – Validation1

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Passive compression validation results

10 20 30 40 50 60 70 80 Angle (deg)

Diabetic foot model

Experimental data Simulated data (zero Achilles force) Simulated data (20% BW Achilles force [near heel lift]) Specific Aim 4: Results – Validation1

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Validation 2: Quiet stance

! Recorded 14 foot retro-reflective markers 1

using 12-camera Vicon system

! Recorded plantar pressure on an emed-x

pressure platform

1 [Leardini et al., Gati & Posture, 25: 453-462

Specific Aim 4: Method – Validation2

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Quiet stance FE simulation

! Prescribed tibia orientation from motion capture data ! Tibial force + Achilles tendon force + gravitational force = 50% BW ! Tune Achilles tendon force to match in vivo COP location

9.81 m/s2 9.81 m/s2 Sagittal view Posterior view

Specific Aim 4: Method – Validation2

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Normal Diabetic

Experimental data Simulated data Experimental data Simulated data Specific Aim 4: Results – Validation2

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Validation 3: Dynamic gait

! Self-selected speed ! Right foot strike ! 7 force plate trials ! 7 pressure platform trials Specific Aim 4: Method – Validation3

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Gait FE simulation

! Different simulation for force plate and pressure platform trials ! Prescribe tibial kinematics-time history (series of 4x4 transformation

matrices)

! Prescribe tendon force-time history from literature 1

1 [Aubin et al., 2012, IEEE T. Robot, 28: 246-255

Specific Aim 4: Method – Validation3

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Gait FE simulation

! Different simulation for force plate and pressure platform trials ! Prescribe tibial kinematics-time history (series of 4x4 transformation

matrices)

! Prescribe tendon force-time history from literature 1 Specific Aim 4: Method – Validation3

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Gait FE simulation: protocol

! Initialize tendon forces, dorsiflex ankle before heel strike (0.0s to 0.2s) ! At 0.2s, switched to prescribed tibial kinematics ! Stance phase of gait ~0.215s to push off

Model tuning to achieve target vertical GRF

! Floor position (1-7mm) ! Achilles tendon force 0.2 0.4 0.6 0.8 1 1.2 50 100 Vertical GRF (BW) Percent stance phase (%) Specific Aim 4: Method – Validation3

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Gait: simulation results

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Gait: simulation results

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0.0 0.2 0.4 0.6 0.8 1.0 1.2 20 40 60 80 100 Vertical GRF (BW) Percent stance phase (%) Normal subject (gait force plate) Experimental data Simulated data

Gait: Vertical ground reaction force

+

Specific Aim 4: Results – Validation3

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0.2 0.4 0.6 0.8 1 1.2 1.4 20 40 60 80 100 Vertical GRF (BW) Percent stance phase (%) Diabetic subject (gait force plate) Experimental data Simulated data

Gait: Vertical ground reaction force

+

Specific Aim 4: Results – Validation3

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Gait: AP shear ground reaction force

+

  • 0.4
  • 0.3
  • 0.2
  • 0.1

0.1 0.2 0.3 0.4 20 40 60 80 100 Anteroposterior shear GRF (BW) Percent stance phase (%)

Normal subject

Experimental data Simulated data

Specific Aim 4: Results – Validation3

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  • 0.3
  • 0.2
  • 0.1

0.1 0.2 0.3 0.4 20 40 60 80 100 Anteroposterior shear GRF (BW) Percent stance phase (%) Diabetic subject Experimental data Simulated data

Gait: AP shear ground reaction force

+

Specific Aim 4: Results – Validation3

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Gait: Center of pressure

Plantar pressure (kPa)

Experimental plantar pressure and COP progression from emed pressure platform (normal subject data)

Normal Diabetic

Specific Aim 4: Results – Validation3

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Gait: Bone kinematics

! Measurements are based on foot model described by Leardini et al.,

2007

! 10 bone angle validations showed small RMS error relative to peak

Normal Diabetic

Specific Aim 4: Results – Validation3

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Gait: Bone-to-ground angles

Specific Aim 4: Results – Validation3

Normal Diabetic

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Gait: Plantar fascia force

! Cadaveric experimental results vs FE model Specific Aim 4: Results – Validation3

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Gait: Ankle joint force

! In vivo inverse dynamic results vs FE model Specific Aim 4: Results – Validation3

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Model prediction

! Internal stress ! Parametric analysis on the effect of soft tissue assumptions

  • n plantar pressure and internal stress

Specific Aim 4: Method – Model prediction

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Model prediction: Internal stress

! 8 locations in the plantar fat (ulcer risk locations) ! Calculated stress in terms of mean Von Mises stress1 ! 1000 elements/region (3000 at the subcalcaneus)

1 [Gefen et al., 2003, Med. Eng. Phys., 6: 491-499

Specific Aim 4: Method – Internal stress

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Model prediction: Internal stress

Specific Aim 4: Results – Internal stress

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Model prediction: Internal stress

Specific Aim 4: Results – Internal stress

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Model prediction: Internal stress

Specific Aim 4: Results – Internal stress

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Model prediction: Internal stress

Specific Aim 4: Results – Internal stress

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Model prediction: Parametric study

! The effect of soft tissue material properties on plantar

pressure and internal stress in quiet stance

" 2X increased plantar fat stiffness " Generic soft tissue assumption " Non-subject-specific soft tissue assumption

Specific Aim 4: Method – Parametric analysis

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Baseline

Baseline Increased plantar fat stiffness Subject-specific generic soft tissue Non-subject- specific material

Quiet stance plantar pressure

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Conclusion

! Subject-specific FE foot models

" Subject-specific anatomy, soft tissue material properties

and tibial kinematics

" Improved plantar fascia component " Improved ligament, tendon structures and joint cavity " Extensive static and dynamic model validations

Specific Aim 4: Conclusion