Modeling the Pelvic Floor using Shell Elements 1 Departamento de Engenharia Civil Instituto Superior Técnico Av. Rovisco Pais Lisboa Portugal 2 S. João Hospital Porto Portugal 3 IDMEC Faculty of Engineering University of Porto Portugal D. d'Aulignac(1), J.A.C. Martins(1), T. Mascarenhas(2), R.M. Natal Jorge(3) and E.B. Pires(1)

2 Plan Anatomy Finite Element Simulation DataGeometry

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

4 Pelvic Floor Illust. From Netter

5 MRI Images Sao Joao Hospital, Porto axialsagittal

6 Visualisation Rasmussen et al (University of Illinois at Chicago) Segmented manually from MRI data. Julia R. Fielding et al. (Harvard medical school)

7 Cadaver Measurements Janda et al 2003

8 Geometry Point Set NURB Surfaces (Rhino 3d) Polygon Mesh

9 Mesh Geometry top side Frontal view of the mesh: 3068 triangles 1620 nodes

10 3D Muscle Model isotropic fibers volume Martins et al. 98

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

12 Muscle Model Fibre strain Direction of fibres (deformed) First Invariant

13 Plane Stress Since incompressibility is assumed Since normal stresses are zero the plane stress is given as

14 Passive Behaviour Humphreys model for cardiac tissue isotropicfibres

15 Passive Tests lambda

16 Muscle Fibres

17 Active Behaviour

18 Muscle Activation Sum of passive and active contributions

19 Total Stress active total isotropic fibers

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

21 Simulation 3068 triangular shell elements Non-linear simulation performed with ABAQUS UMAT routine decribing the material

22 Muscle Activation

23 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)

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