Abstract
Vertebral Body Tethering (VBT) surgery for skeletally immature idiopathic scoliosis (IS) patients involves anteriorly placed vertebral screws securing a deformable Polyethylene-Terephthalate (PET) tether. Before securing the tether, compressive force is applied between the screw heads along the axis of the spine. There are no clear guidelines regarding the force magnitude required to optimize deformity correction. In the current study, a validated, patient-specific finite element (FE) model of the thoracolumbar spine/ribcage for a 10-year-old IS patient was analysed, to investigate the effect of four different VBT loading scenarios on spinal alignment and biomechanics.
The patient-specific FEM was previously validated using clinical results for pre-/post-operative deformity. Linear elastic continuum elements (PET material) were used to tether laterally oriented screws at spinal levels T5–T12, with roughened contact simulating the screws when locked onto the tether. Compressive forces measured intra-operatively during VBT and during anterior scoliosis fusion surgery (FS) were the basis for the four loadcases. The inferior L5 endplate was fixed.
After the surgical loadcases, patient-specific, level-wise gravitational loads at all vertebral levels simulated standing. In this preliminary series of VBT analyses, model predictions for corrected Cobb angle/Kyphosis angle/Axial trunk rotation, correction in major curve intervertebral disc wedge angle; and vertebral bone stress, were compared to determine how different surgical tether tension magnitudes affected deformity correction/spinal loading.
Results demonstrated varying degrees of improvement in coronal deformity correction could be achieved with different patterns of tethering loads. However, resultant loads on surrounding anatomy must be considered, with associated high spinal tissue loads and increased propensity for asymmetric growth modulation with increasing tether forces.
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Little, J.P., Labrom, R.D., Askin, G.N. (2020). A Preliminary Sensitivity Study of Vertebral Tethering Configurations Using a Patient-Specific Finite Element Model of Idiopathic Scoliosis. In: Ateshian, G., Myers, K., Tavares, J. (eds) Computer Methods, Imaging and Visualization in Biomechanics and Biomedical Engineering. CMBBE 2019. Lecture Notes in Computational Vision and Biomechanics, vol 36. Springer, Cham. https://doi.org/10.1007/978-3-030-43195-2_9
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