THE USE OF FINITE THE USE OF FINITE ELEMENTS IN ELEMENTS IN - - PowerPoint PPT Presentation

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THE USE OF FINITE THE USE OF FINITE ELEMENTS IN ELEMENTS IN SURGICAL SURGICAL PROCEDURES PROCEDURES

Djenane C. Pamplona

Laboratory of Membranes and Biomembranes

Civil Engineering Department Catholic University of Rio de Janeiro - Brazil

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Rio/Cambridge Rio/Cambridge

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Djenane Djenane

Age: 23 Age: 44 Age: 30 Age: 54 Prof.Ivo Pitanguy

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Book

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Topics Topics

• The Use of Skin Expanders and a Constitutive

The Use of Skin Expanders and a Constitutive Equation for the Skin. Equation for the Skin.

• Breast Reconstruction with Adjustable Implants:

Breast Reconstruction with Adjustable Implants: a Numerical Analysis. a Numerical Analysis.

• Numerical Model to Describe the Surgery of

Numerical Model to Describe the Surgery of Breast Reduction. Breast Reduction.

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THE USE OF SKIN EXPANDERS AND A CONSTITUTIVE EQUATION FOR THE SKIN

Doctorate Student: Claudio Ribeiro Carvalho

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Skin Expanders Skin Expanders

Skin expander is a silicone bag implanted under the skin which is gradually (weekly) filed with a saline solution. The objective is to expand the skin. Natural skin expansion

• ccurs in pregnancy.

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Skin Expansion is used to: Skin Expansion is used to:

Obtain extra skin to reconstruct

burned areas;

breast reconstruction; eliminating tattoos and scars; extra skin with the desired

color and texture.

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The aim of this research is: The aim of this research is:

To understand the behavior of the skin under expansion. To identify the the material parameters for the skin under

expansion.

To help doctors to know the number and shape of the

skin expanders they should use to obtain an extra amount

• f skin.

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Our study in the clinic Our study in the clinic

Expansion of the scalp Filling the expander

To study the behavior of the skin (human scalp) under expansion, it was necessary to develop an apparatus to measure the pressure inside the skin expander while it was inflated.

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Reconstruction Surgery Reconstruction Surgery

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The apparatus The apparatus

Measuring pressure. Connecting the syringe.

The apparatus is coupled to a syringe and a needle in a way that the pressure inside the skin expander can be measured before, during and after inflation.

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Experimental Results: Experimental Results: Curves Pressure x Volume Curves Pressure x Volume

Skin Expansion - 6 stages

Volume ( ml)

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The skin is considered:

A non linear viscoelastic material; incompressible; homogeneous; isotropic; large deformations. The model is simplified since the skin is not homogeneous nor isotropic and its properties varies from one site to the other. It changes with sex, age, race and exposure to the sun.

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Viscoelastic Viscoelastic Behaviour Behaviour: :

W : Constitutive Relation. a and b : Parameters of the material. I1: First principal invariant of the Cauchy-Green deformation tensor.

      − − = 1 ) 3 I ( 2 b exp( b a W

1

Delfino Delfino’ ’s s Constitutive Equation Constitutive Equation Integral formulation for relaxation Integral formulation for relaxation

' dt ' dt d ) ' t t ( G 2 ) t (

t

∫

ε − = σ

G ( t ) : Relaxation function

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Finite Element Model ABAQUS

Circular skin expander

Triangular and quadrilateral membrane and fluid elements.

Boundary Condition

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Animation for a circular expander Animation for a circular expander

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Numerical Results 1 Numerical Results 1st

st stage

stage

Using the least-square fit procedure minimizing the error, the material coefficients at the first stage (volume 80 – 110 ml) are : a= 0.213 MPa and b=31.5.

0,00 0,50 1,00 1,50 2,00 2,50 3,00 3,50 70,00 80,00 90,00 100,00 110,00 120,00 Volume (ml) Pressure (N/cm2) Experimental C1 C2 C3 C4 C5

The same procedure was used in the following stages, until volume from 538 ml is reached.

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Results for the Scalp Results for the Scalp

Constant a scalp

0.000 0.500 1.000 1.500 2.000 2.500 3.000 0.00 0.50 1.00 1.50

Current volume/initial volume (X100)

Constant a (MPa)

Experimental

Constant b scalp

0.0 20.0 40.0 60.0 80.0 0.00 0.50 1.00 1,50

Current volume / initial volume (X100) Constant b experimental Fase Vfinal/Vo a (Mpa) b A 80 x x x 1 80 110 0.28 0.213 31.5 2 110 140 0.35 0.222 33.4 B 140 380 x x x 3 380 425 1.06 0.986 51.3 4 425 465 1.16 1.298 75.2 5 465 500 1.25 1.463 134.5 6 500 538 1.35 1.787 120.5 initial - final

Experimental results - Pacient 1

Volume (ml) Constants Fase Vfinal/Vo a (Mpa) b A 214 x x x 1 214 254 0.85 0.636 42.6 2 254 298 0.99 0.491 48.2 3 298 338 1.13 1.007 49.8 4 338 376 1.25 1.500 65.6

Experimental results Pacient 2

Volume (ml) initial - final Constants

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Our Patients Until Now Our Patients Until Now

Patient 2 Patient 3 Patient 4 Patient 5 Patient 1

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Discussion Discussion

The numerical model developed was successful in its

purpose to understand the process of skin expansion. This is the first step towards this research. Other patients and other sites are been studied.

It was possible to understand the limiting stress during the

skin expansion (pain). A complete model should be developed to help the surgeon to decide the number and shape of the expanders in view of the desired final size of skin. Other constitutive equations should be used.

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Conclusions Conclusions

Different regions: Scalp: more rigid larger values for constant a. Abdomen and leg : similar values for constant a. A parammetric study involving the thickness of the skin: showed the necessity to have it correctly measured during the surgery. Fatty regions: It was verified the importance of the amount of fatty tissue in the behaviour of the skin expansion.

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Future Work Future Work

More patients, with different regions of the body,

discriminating race and age must be done..

Experimental study to verify the importance of the elastic

foundation (fatty base) in the expansion.

Reliable skin thickness to work with.. Measure the relaxation process. Propose number, shape and size of the skin expander for

doctors.

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Doctorate Student: Doctorate Student: Cristina Cristina de A. de A. Alvim Alvim

BREAST RECONSTRUCTION WITH BREAST RECONSTRUCTION WITH ADJUSTABLE IMPLANTS: ADJUSTABLE IMPLANTS: A NUMERICAL ANALYSIS A NUMERICAL ANALYSIS

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Breast Reconstruction with Expanders Breast Reconstruction with Expanders and Implants and Implants

Relative Simplicity; Covering tissue with similar texture, color and sensation; Less scars; Reduced surgery and post-surgery recovery time. Avoidance of distant donor-site morbidity;

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Expanders and Implants Expanders and Implants

Round Expanders and Implants: High and low profile; cheaper; used in round breast without ptosis. Anatomic Expanders and Implants: Natural appearance, but more expensive.

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Steps: Steps:

1 . After mastectomy, an expander is inserted beneath the skin, near the region to be reconstructed.

• 2. The expander is gradually

filled, in periodical steps, until reaching the double of the desired volume (volume of the implant) .

• 3. The expander is removed and a

permanent implant is then inserted. A third surgery may be recommended to reconstruct the nipple.

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Objectives: Objectives:

Analyze the stresses and strains that occur in skin immediately after breast reconstruction, to suggest the refinement of surgical techniques and search for new expanders and implants. Verify the stresses distribution with the use of radiotherapy and the influence of the scar position. Improve the expansion process, optimizing the number, shape and size of the expander, according to the patient.

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Expander Anatomic Implant

570 ml R= 12 cm

B C A

285 ml A = 11.3 cm B = 10.3 cm C = 4.3 cm

Computational Modeling of Computational Modeling of Breast Reconstruction Breast Reconstruction

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Skin: mechanical behavior Skin: mechanical behavior

Skin µ 1 = 0,788 kPa

( )

3 2 W

i i i

2 2 1 N 1 i 2 i

− λ + λ + λ α µ =

α α α =

∑

Ogden’s Contitutive Equation: α 1 = 6.927 Hyperelastic term: Viscoelastic term (relaxation function)

( )

∑

= τ −

− − =

N 1 i t i R

i

e 1 g 1 ) t ( g

Prony: Skin and Scar g1 = 0.386 kPa τ1 = 43.22 Scar µ1 = 2.3464 kPa α 1 = 6.927

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Bilateral mastectomy Breast been expanded

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Finite Element Model ABAQUS/Explicit: Finite Element Model ABAQUS/Explicit:

749 Membrane Element (M3D3) 500 Solid Element (C3D8) with fluid properties. Solid Implant

(h = 6 mm; 8 mm in the scar)

Skin

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Expansion; Prosthesis+; Relaxation

Maximum stresses (N/cm2)

With Scar

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Expansion; Prosthesis+; Relaxation

Maximum stresses (N/cm2)

With Scar

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Discussion and Conclusion Discussion and Conclusion

• The finite element model was successful to represent

The finite element model was successful to represent the surgery of breast reconstruction. the surgery of breast reconstruction.

• The model pointed the direction in witch new breast

The model pointed the direction in witch new breast expanders should be developed to satisfy skin expansion expanders should be developed to satisfy skin expansion in breasts where radiotherapy was need and when the in breasts where radiotherapy was need and when the scars are centered. scars are centered.

Future Work Future Work

Influence of scar position and mechanical properties. Gravity: the weight of reconstructed breast. New models of expanders

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NUMERICAL MODEL TO DESCRIBE THE SURGERY OF BREAST REDUCTION

Doctorate Student: Doctorate Student: Cristina Cristina de A. de A. Alvim Alvim

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Breast reduction can be a necessary procedure in cases

• f pathological breast sizes that can interfere with the

health of women. The The breast breast: :

The breast is composed basically by mammary glands in the internal part of the breast. The fatty tissue is responsible for the rest of the composition. The proportion of each one differs from

• ne woman to another.

The glandular tissue is more rigid than the fatty.

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The aim of the work is to use a finite element model to perform a study to determine the best type of surgery resection for each type of breast.

• Prof. I. Pitanguy developed both techniques used.

Areola Infra mammary fold

Technique of the surgery [ Technique of the surgery [Pitanguy Pitanguy, , 2000]. 2000].

Three points are marked forming a triangle around the areola of the breast and two points more in the infra mammary fold, considered a constraint. The incisions are made according to the figure.

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A B

After the parenchyma resection, the breast is reconstructed. Depending of the type of the breast (more glandular or more fatty) two types of resections can be used: Straight is used in breasts with more fatty tissue. Inverted Keel is used in breasts with more mammary glands.

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Ogden

( )

∑

= α α α

− λ + λ + λ α µ =

2 1 i 3 2 1 2 i i

3 2 W

i i i

* *Experimental Results Samani [2001].

µ1 (kPa) α1 Fatty Tissue* 1.8567 18.1468 Skin 0.803 6.8206 Mammary Glands* 9.0657 25.0000 MATERIAL

Mechanical Properties: Mechanical Properties:

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Simulation in a 500 cm Simulation in a 500 cm3

3 breast.

breast.

Making used of the extrusion and rotation tools of the pre- processor ABAQUS/CAE, the surgery is simulated.

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Surgery with Straight Resection Surgery with Straight Resection ( (indication for fatty breast)

indication for fatty breast) The parenchyma resection is of 80 cm3

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The breast was modeled with properties of mammary glands (pink) and fatty tissue

(yellow)

with different proportions. The skin is modeled as a membrane with 0.7 mm of thickness (435 elements with 3 nodes – M3D3) using the external FE nodes of the breast.

The model for the breast has 5844 elements (C3D4). MOD2a MOD2b

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Maximum stresses (N/cm2)

Straight Resection: Straight Resection: fatty breast

fatty breast

T=0: lying and upright position. 3 weeks

Nipple

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Maximum stresses (N/cm2)

Straight Resection: Straight Resection: glandular breast

glandular breast

T=0: lying and upright position. 3 weeks

Nipple

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We can observe the change of the profile described by the

• surgeons. There is no ptosis in fatty breast.

It was possible to observe the upward movement of the nipple with time. This is a very tricky behavior for the surgeons. The fatty breast gives a satisfactory simulation of the surgery with the desired projection for the superior part of the breast. In the more glandular breast there is an exaggerated upward projection of the nipple after tree weeks . There are concentration of stresses in the region of the suture, especially in the infra mammary fold(observed by Chretien-Marquet et al [1999]).

Discussion and Conclusion Discussion and Conclusion

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FUTURE WORK FUTURE WORK

Surgery with Inverted Keel (indicated for breast with Surgery with Inverted Keel (indicated for breast with more mammary glands) more mammary glands)

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Acknowledgements Acknowledgements

• Center of Studies Prof. Ivo Pitanguy
• Dr. Sergio Carreirão
• Dr. Henrique Radwanski
• FAPERJ
• CNPq
• 38a Division of Santa Casa da Misericórdia-RJ