3D correction of AIS in braces designed using CAD/CAM and FEM: a randomized controlled trial

Background: Recent studies showed that finite element model (FEM) combined to CAD/CAM improves the design of braces for the conservative treatment of adolescent idiopathic scoliosis (AIS), using 2D measurements from in-brace radiographs. We aim to assess the immediate effectiveness on curve correction in all three planes of braces designed using CAD/CAM and numerical simulation compared to braces designed with CAD/CAM only. Methods: SRS standardized criteria for bracing were followed to recruit 48 AIS patients who were randomized into two groups. For both groups, 3D reconstructions of the spine and patient's torso, respectively built from bi-planar radiographs and surface topography, were obtained and braces were designed using the CAD/CAM approach. For the test group, 3D reconstructions of the spine and patient's torso were additionally used to generate a personalized FEM to simulate and iteratively improve the brace design with the objective of curve correction maximization in three planes and brace material minimization. Results: For the control group (CtrlBraces), average Cobb angle prior to bracing was 29 degrees (thoracic, T) and 25 degrees (lumbar, L) with the planes of maximal curvature (PMC) respectively oriented at 63 degrees and 57 degrees on average with respect to the sagittal plane. Average apical axial rotation prior to bracing was 7 degrees (T) and 9 degrees (L). For the test group (FEMBraces), initial Cobb angles were 33 degrees (T) and 28 degrees (L) with the PMC at 68 degrees (T) and 56 degrees (L) and average apical axial rotation prior to bracing at 9 degrees (T and L). On average, FEMBraces were 50% thinner and had 20% less covering surface than CtrlBraces while reducing T and L curves by 47 and 48%, respectively, compared to 25 and 26% for CtrlBraces. FEMBraces corrected apical axial rotation by 46% compared to 30% for CtrlBraces. Conclusion: The combination of numerical simulation and CAD/CAM approach allowed designing more efficient braces in all three planes, with the advantages of being lighter than standard CAD/CAM braces. Bracing in AIS may be improved in 3D by the use of this simulation platform. This study is ongoing to recruit more cases and to analyze the long-term effect of bracing.