Biomechanical modelling of orthotic treatment of the scoliotic spine including a detailed representation of the brace-torso interface.

Abstract

As part of the development of new modelling tools for the simulation and design of brace treatment of scoliosis, a finite element model of a brace and its interface with the torso was proposed. The model was adapted to represent one scoliotic adolescent girl treated with a Boston brace. The 3D geometry was acquired using multiview radiographs. The model included the osseo-ligamentous structures, thoracic and abdominal soft tissues, brace foam and shell, and brace-torso interface. The simulations consisted of brace opening to include the patient's trunk followed by brace closing. To validate the model, the resulting geometry was compared with the real in-brace geometry, and the resulting contact reaction forces at the brace-torso interface were compared with the equivalent forces calculated from pressure measurements made on the in-brace patient. Differences between coronal equivalent and reaction forces were less than 7N. However, sagittal reaction forces (47N) were computed on the abdomen, whereas negligible equivalent forces were measured. The simulated geometry presented partially reduced coronal Cobb angles (1-4 degrees), over-corrected sagittal Cobb angles and maximum deformation plane (5 degrees), completely corrected coronal shift, and sagittal shift and rib humps that were not corrected. This study demonstrated the feasibility of a new approach that represents the load transfer from the brace to the spine more realistically than does the direct application of forces.