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.
Scoliosis Scoliosis = Three dimensional deformation of the spine and rib cage
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
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.
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)
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.
Personalized Geometrical Model Aubin, 1995 X-Rays 3D Reconstruction (Wireframe Model) Detailed 3D Geometrical Model
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
Brace Model : Generative Curves Brace upper limit Thoracic apex Lumbar apex Pelvic section
Generative Curves Definition coupe 6 shape parameters, 3 position parameters
Brace Surfacic Model Generative Curves Surfacic Model Creation of Openings Creation of Pads
Biomechanical Finite Element Model of the Brace Extern shell : Polyethylene Shell elements Pads : Polyethylene foam Hexaedric elements Interface brace – human torso : contact elements
Simulation : 1) Brace Opening
Simulation : 2) Brace Placement on The Patient
Simulation : 3) Tightening of Straps
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
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 ↓.
Results : Geometry For all braces, equivalent corrections.
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 …
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.
Acknowledgements