Modélisation biomécanique de la chirurgie par modulation de croissance de la colonne vertébrale scoliotique : analyse pour prévenir les déformations périphériques subséquentes

Two to 3% of children have scoliosis, a 3D spinal deformity, of which 80% are idiopathic, i.e. without a known origin. For severe scoliosis (Cobb angle >45°) or with high growth potential, surgical treatment is required to stop the progression of the curvature. The most commonly used surgical procedure currently involves a spinal fusion, making it very impactful on the patient's quality of life due to the loss of mobility that it entails. To avoid this, the Anterior Vertebral Body Tethering (AVBT) a fusionless device by growth modulation, has been developed using an approach based on the Hueter-Volkman principle. This principle states that compressive loading on the growth plates inhibits growth while a distractive force stimulates it. The AVBT compresses the convex side of the curvature with a tether attached to the side of the vertebral bodies to inhibit growth and promote expansion on the concave side. Then, by growth modulation, the spine gradually straightens out over time and with growth. AVBT is therefore a promising method since it preserves the patient's mobility and does not require periodic follow-up surgery to straighten the spine. Nevertheless, currently implanted empirically by orthopedic surgeons, there is still a lack of knowledge about its long-term effects, particularly about the risks of cable breakage, overcorrection or subsequent deformities (adding-on). The latter may occur on non-instrumented spinal curvatures after AVBT implantation. Thus, the distal curvature underlying the instrumentation could undergo further postoperative deformation due to the implant, or, on the contrary, stabilize or even improve. To help predict such evolution, it is necessary to understand and study the effect of biomechanical parameters involved in distal non-instrumented segment evolution in order to predict the effect of the device on the entire spine. The objective of this thesis was to develop a biomechanical analysis technique to predict distal secondary peripheral deformities induced by implantation of a fusionless AVBT device for pediatric scoliosis. The hypothesis to be tested was that the evolution of lumbar curvature following AVBT instrumentation can be predicted by the wedging angle of the disc and the asymmetry of forces under the lower instrumented vertebrae (LIV). For this purpose, a biomechanical finite element model based on the 3D reconstruction of patients treated with AVBT was used. This model includes the spine and its pre-, intra- and postoperative positioning as well as the implantation of the AVBT device on the vertebrae and its tensioning.