Biomechanical modeling of brace treatment of scoliosis: effects of gravitational loads.

The biomechanics of bracing in adolescent idiopathic scoliosis is still not fully understood. Finite element models (FEM) have been used but the gravity forces were not included and the production of spinal stresses not evaluated. An improved FEM to simulate brace treatment was thus developed. The 3D geometry of the spine, rib cage, pelvis, and of the trunk external surface of five scoliotic patients was acquired using a multi-view X-ray technique and surface topography. A FEM of the patient's trunk including gravity forces was created. Custom-fit braces were modeled and their installation simulated. Immediate geometrical corrections and pressures were computed and validated. The resulting compressive loads on the vertebral endplates were quantified. The influence of the strap tension, spine stiffness, and of the gravity forces was evaluated. Results showed that the brace biomechanical action was importantly to prevent the scoliotic spine from bending under the gravity forces. The immediate correction depended on the strap tension and spine stiffness. The distribution and amplitude of computed pressures were similar to those measured with the real braces. After the brace installation, the coronal asymmetrical compressive loading on the vertebral endplates was significantly reduced. In conclusion, the model developed presents improvements over previous models and could be used to better understand and optimize brace treatment.