Modeling the Pelvic Floor using Shell Elements

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Modeling the Pelvic Floor using Shell Elements
D. d'Aulignac(1), J.A.C. Martins(1), T.
Mascarenhas(2), R.M. Natal Jorge(3) and E.B.
Pires(1)
3IDMECFaculty of EngineeringUniversity of
Porto Portugal
1Departamento de Engenharia Civil Instituto
Superior Técnico Av. Rovisco Pais 1049-001
Lisboa Portugal
2S. João HospitalPortoPortugal
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Plan
Finite Element Simulation
Anatomy
Data
Geometry
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Why?

• Understand working of the pelvic floor
• Support of organs
• Predict damages during childbirth
• Stress incontinence
• Prolapse
• Uterine
• Vaginal
• Rectal

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Pelvic Floor
Illust. From Netter
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MRI Images
Sao Joao Hospital, Porto
axial
sagittal
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Visualisation

• Segmented manually from MRI data. Julia R.
  Fielding et al. (Harvard medical school)

Rasmussen et al (University of Illinois at
Chicago)
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Cadaver Measurements
Janda et al 2003
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Geometry
Point Set
NURB Surfaces (Rhino 3d)
Polygon Mesh
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Mesh Geometry
top
Frontal view of the mesh 3068 triangles 1620
nodes
side
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3D Muscle Model
Martins et al. 98
isotropic
fibers
volume
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Muscle Model
Deformation gradient
Left Cauchy-Green tensor
Right Cauchy-Green tensor
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Muscle Model
First Invariant
Fibre strain
Direction of fibres (deformed)
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Plane Stress
Since incompressibility is assumed
Since normal stresses are zero the plane stress
is given as
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Passive Behaviour
isotropic
fibres
Humphreys model for cardiac tissue
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Passive Tests
u
lambda
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Muscle Fibres
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Active Behaviour
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Muscle Activation
Sum of passive and active contributions
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Total Stress
isotropic
total
active
fibers
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Discussion

• Large quantitative differences between different
  models
• Oomens
• Martins
• Bosboom
• Gielen
• Kojic
• Humphrey
• Comparison with other models and experimental
  results is essential

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Simulation
3068 triangular shell elements Non-linear
simulation performed with ABAQUS UMAT routine
decribing the material
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Muscle Activation
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The Future

• Deformation of pelvic floor during childbirth
• Damage, fracture of soft tissues
• Prolapse of internal organs
• Geometric models from MRI data
• 8-node solid FE (de Sousa et al. 03)

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Muscle Model
Deformation gradient
Left Cauchy-Green tensor
Right Cauchy-Green tensor