FEM With CAD/CAM Brace Design Improves Curve Correction in AIS

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Recent studies have shown that a finite element model (FEM) combined with CAD/CAM improves the design of braces for the conservative treatment of adolescent idiopathic scoliosis (AIS), using 2D measurements from in-brace radiographs. FEM is a numerical method commonly used for solving engineering and mathematical physics problems. A recent study assessed the immediate effectiveness on curve correction in all three planes of braces designed using CAD/CAM and the numerical simulation of FEM, compared to braces designed with CAD/CAM only. The researchers found that combining FEM with the CAD/CAM approach allowed them to design more efficient braces in all three planes that were lighter than standard CAD/CAM braces. The study, whose initial results were published July 23 in Scoliosis and Spinal Disorders, is ongoing to recruit more cases and to analyze the long-term effect of bracing.

For the current publication, researchers recruited 48 patients with AIS who were randomized into two groups. Inclusion criteria were a diagnosis of AIS (Cobb angle of 20-40 degrees), a Risser sign of 0-2, and a prescription for full-time TLSO wear. For both groups, 3D reconstructions of each patient's spine and torso from biplanar radiographs and surface topography were completed, and braces were designed using CAD/CAM. For the test group, the 3D reconstructions were also 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. Braces were designed by one of two participating orthotists who had more than 10 years of experience with TLSO fabrication and two years of experience with CAD/CAM technology.

In the control group, the average Cobb angle prior to bracing was 29 degrees thoracic and 25 degrees lumbar, with the planes of maximal curvature 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 thoracic and 9 degrees lumbar. For the test group, initial Cobb angles were 33 degrees thoracic and 28 degrees lumbar, with the planes of maximal curvature at 68 degrees thoracic and 56 degrees lumbar, and average apical axial rotation prior to bracing at 9 degrees thoracic and lumbar.

On average, the FEM braces were 50 percent thinner and had 20 percent less covering surface than the control group while reducing thoracic and lumbar curves by 47 percent and 48 percent, respectively, compared to 25 percent and 26 percent for the control group. The FEM races corrected apical axial rotation by 46 percent compared to 30 percent for the control group.