1. BIOMECHANICAL STUDY OF THE DESIGN PARAMETERS OF A BRACE FOR THE TREATMENT OF SCOLIOSIS
Julien Clin, Carl-Éric Aubin, Hubert Labelle
Institut de génie biomédical, École Polytechnique de Montréal.
Hôpital Sainte-Justine, Centre de recherche.

2. Scoliosis
Scoliosis = Three dimensional deformation of the spine and rib cage

3. Brace Treatment in AIS
Long-term goal : To stop the progression of scoliotic deformities.
Short-term goal : To maximally correct scoliotic deformities by applying adequate forces on the human torso.
Opening
Pad

4. Brace Treatment Issues
Efficiency in frontal plane generally admitted (Nachemson, 1995) but the 3D correction of scoliotic deformities is still an issue (Labelle, 1996).
Biomechanics remain not well understood. Design is based mostly on empirical considerations.
Some design parameters (symmetry of the shape, pads position, strap tension, openings, abdominal force) are still discussed.

5. Brace Treatment Simulations
Former method : To apply forces on a finite element model of the human torso.
Limit : Do not allow studying directly design of braces
Périé, Aubin and al. (2004)

6. Objective
To develop a parametric detailed model of a brace and a simulation of its immediate effect. This model must allow studying the design of a brace and optimizing it.

7. Personalized Geometrical Model
Aubin, 1995
X-Rays
3D Reconstruction (Wireframe Model)
Detailed 3D Geometrical Model

8. Biomechanical Finite Element Model of the Human Torso
Aim : To calculate deformations of the osseo-ligamentous system when forces are applied.
Different anatomic components of spine, rib cage, pelvis and abdomen are modeled.
Patient-specific geometry, mechanical properties are derived from experimental data
Descrimes, Aubin, 1995, Périé, 2001

9. Brace Model : Generative Curves
Brace upper limit
Thoracic apex
Lumbar apex
Pelvic section

10. Generative Curves Definition
coupe
6 shape parameters, 3 position parameters

11. Brace Surfacic Model Generative Curves Surfacic Model
Creation of Openings
Creation of Pads

12. Biomechanical Finite Element Model of the Brace
Extern shell : Polyethylene Shell elements
Pads : Polyethylene foam
Hexaedric elements
Interface brace – human torso : contact elements

13. Simulation : 1) Brace Opening

14. Simulation : 2) Brace Placement on The Patient

15. Simulation : 3) Tightening of Straps

16. Experimentation Plan
Experimentation Plan: Box, Hunter & Hunter, Full Factorial
Factor
Modality 1
Modality 2
Modality 3
Friction
0.4
0.8
Shell Stiffness
1000 MPa
2000 MPa
Pad Stiffness
10 MPa
20 MPa
Size
1 ( Tight )
2 ( Large )
Strap Tension
20 N
40 N
60 N
Symmetric Shape

17. Results : Forces Pad Stiffness and Friction effect on forces is weak.
Most influential factor = Strap Tension.
Pad Stiffness and Friction effect on forces is weak.
Forces ↑ when Strap Tension ↑ , Shell stiffness ↑ or when Size ↓.

18. Results : Geometry
For all braces, equivalent corrections.

19. Limits Mechanical properties are generic.
Only passive action of the brace has been studied.
Mechanical properties are generic.
Optimization study was preliminary but showed the potential of the model.
Other parameters to study : geometry, pads position, openings position, strap position …

20. Conclusion We showed the feasibility of this approach.
When completely validated, this model would represent an advanced tool for the study of brace design parameters.

21. Acknowledgements