Biomechanical Analysis of Scoliosis Adjusted by Screw Fixation System with Finite Element Analysis

Abstract

Adolescent Idiopathic Scoliosis is the most common type of scoliosis. The popular scoliosis treatment is scoliosis bracing or surgical treatment. The Cobb method is generally used to measure the scoliosis curvature angle for the surgeon in order to plan the treatment process. In addition, the Cobb angle of 40 degrees often creates a difficulty for surgeons in selecting the suitable treatment for the patients because the Cobb angle of 40 degrees is, in general, indicated as too large for scoliosis bracing although is not large enough to be indicated for surgical treatment. Therefore, this research investigated the relationship between the deformity of the Cobb angle between 30-70 degrees adjusted by the screw fixation system and evaluated the maximum equivalent of total strain distribution on the 3D models using the finite element analysis. All model cases were calculated with nonlinear ligament forces. The result showed a correlation between larger Cobb angles with higher maximum equivalent of total strain occurred on the vertebra, mainly resulted from the Rebound Force. The larger Cobb angle has resistance from the tendon and the muscles against the restoring force of the fixation devices adjusting the curvature of scoliosis. For this reason, the scoliosis patients with small Cobb angle are advised to be treated with surgery before the Cobb angle reaches 70 degrees in order to reduce the risk of damage on the vertebra, the fixation device, and the unsuccessful result of surgery.