Étude biomécanique du processus de croissance et de déformation du rachis scolitotique

Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional (3D) anomaly of the spine and rib cage, involving intrinsic alterations of spinal tissues, mainly the wedging of vertebral bodies and intervertebral disks.

The clinical part of this project involves the 2D and 3D in vivo characterization of scoliotic deformities. It is hypothesized that there are relationships between spinal curvatures and vertebral and intervertebral deformities, and that spinal and vertebral deformation patterns differ for thoracic and lumbar curves.

Several 2D and 3D scoliotic descriptors were evaluated analytically based on 3D reconstruction of spinal structures using a multiview radiographic technique applied on scoliotic patients. Statistical analyses were completed to establish relationships between regional and local descriptors and to analyze the evolution of deformities between two visits in clinics. The biomechanical model was based on experimental and clinical observations (Hueter-Volkmann law), and was formulated with variables integrating a biomechanical stimulus of growth modulation, a sensitivity factor to the stimulus and time. It was integrated into a finite element model of the thoracic and lumbar spine using an iterative procedure. This model was personalized to the geometry of a non-pathologic female subject without spinal deformity. Five AIS pathogenesis hypotheses, as well as several other initiating conditions, were represented in terms of initial geometrical eccentricities of the reference spinal configuration, and used to trigger the self-sustaining deformation process.

Based on the biomechanical studies, there is not a unique initiating condition that results in the development of scoliotic deformities. At this stage of development, the use of this modeling approach as a prediction tool of scoliosis progression is restrained by mechanical properties of vertebral tissues and parameters of growth and growth modulation, which are difficult to determine for a given patient. Limits also include the assumptions related to the parameters of growth modulation, which are presently not well documented experimentally for the human. Accuracy associated with the 3D reconstruction methods and the analytical evaluation of regional and local scoliotic descriptors, as well as the altered natural history by bracing of the scoliotic sample, must be reminded as limits of the clinical results. (Abstract shortened by UMI.)