• Nikita Cobetto, Stefan Parent, and Carl-Eric Aubin.
• Department of Mechanical Engineering, Polytechnique Montréal, P.O. Box 6079, Downtown Station, Montreal, Quebec H3C 3A7, Canada; Research Center, Sainte-Justine University Hospital Center, 3175 Côte-Sainte-Catherine Road, Montreal, Quebec H3T 1C5, Canada.
• Clin Biomech (Bristol, Avon). 2018 Jan 1; 51: 26-33.

BackgroundAnterior vertebral body growth modulation is a fusionless instrumentation to correct scoliosis using growth modulation. The objective was to biomechanically assess effects of cable tensioning, screw positioning and post-operative position on tridimensional correction.MethodsThe design of experiments included two variables: cable tensioning (150/200N) and screw positioning (lateral/anterior/triangulated), computationally tested on 10 scoliotic cases using a personalized finite element model to simulate spinal instrumentation, and 2years growth modulation with the device. Dependent variables were: computed Cobb angles, kyphosis, lordosis, axial rotation and stresses exerted on growth plates. Supine functional post-operative position was simulated in addition to the reference standing position to evaluate corresponding growth plate's stresses.FindingsSimulated cable tensioning and screw positioning had a significant impact on immediate and after 2years Cobb angle (between 5°-11°, p<0.01). Anterior screw positioning significantly increased kyphosis after 2years (6°-8°, p=0.02). Triangulated screw positioning did not significantly impact axial rotation but significantly reduced kyphosis (8°-10°, p=0.001). Growth plates' stresses were increased by 23% on the curve's convex side with cable tensioning, while screw positioning rather affected anterior/posterior distributions. Supine position significantly affected stress distributions on the apical vertebra compared to standing position (respectively 72% of compressive stresses on convex side vs 55%).InterpretationThis comparative numerical study showed the biomechanical possibility to adjust the fusionless instrumentation parameters to improve correction in frontal and sagittal planes, but not in the transverse plane. The convex side stresses increase in the supine position may suggest that growth modulation could be accentuated during nighttime.Copyright © 2017 Elsevier Ltd. All rights reserved.

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