| Zdroj: |
Aachen : RWTH Aachen University, Report. IAM, Institute of General Mechanics 19, 1 Online-Ressource : Illustrationen, Diagramme (2023). doi:10.18154/RWTH-2023-04766 = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023.-Dissertation, Federal University of Santa Catarina Florianópolis, 2023 |
| Popis: |
Anterior vertebral body tethering (AVBT) is an innovative fusionless surgery technique for the treatment of adolescent idiopathic scoliosis, where anchors and screws are inserted into the vertebral bodies at the lateral convex side of the spine. Subsequently, a flexible cord (tether) is connected to the screws heads while tension is applied to correct the spine deformity and stop its progression while allowing for continued spinal growth and mobility. To reduce the risk of tether breakage, surgeons introduced new configurations such as the use of an additional tether (double-tether) or a short rigid rod connecting some of the tethered vertebrae (hybrid). The first objective of this study is to experimentally investigate the kinematics of the human thoracolumbar spine (T10-L3) instrumented with AVBT considering single-tether, double-tether and hybrid technique inserted in the left side. Secondly, to numerically investigate the effects of cord tension within AVBT with single-tether. For that purpose, a Finite Element model the spine was developed. Identification algorithms were implemented to automate the complex task of calibration of the material properties while reducing the error between the numerical and the experimental moment-range of motion curves. The experimental results are derived from a stepwise resection study with human L1-L2 spinal specimens considering cuts of each ligament and the vertebral arches. The material properties of each spinal structure was calibrated individually in a stepwise manner. The flexibility tests were performed with custom-built machines capable of loading the spinal specimens in pure moment. The experimental results showed that the tested AVBT techniques preserved the global (T10-L3) range of motion (ROM) of the native spine in flexion–extension (> 90%) and axial rotation (> 87%) but reduced to approximately 30% in left lateral bending and 43% in right lateral bending. After calibration, the Finite Element model was capable of reproducing the experimental results in all loading directions and resection stages. The numerical stress-stretch ratio curves from tensile tests of single lamellae, angle of the fibers, ROM of the spine under combined loading and forces at facet joints also agreed with the experimental data. The L1-L2 model bended to the implant side 2.73°, 4.35°, and 5.35° for tether tension forces of 100 N, 200 N, and 300 N, respectively. Considering the postoperative position of the spine as the reference position, the ROM of the instrumented L1-L2 spine under 6 Nm in right lateral bending was 1.8°, 1.6°, and 1.4° for a cord pretension of 100 N, 200 N and 300 N, respectively, while the native spine was 4.5°. The single tether, double-tether and hybrid are motion preservation techniques for flexion-extension and axial rotation. The stiff tether provides primary stability to the spine and the cord pretension adds stiffness to the spine for lateral movement. |
