Expérimentation et modélisation détaillée de la colonne vertébrale pour étudier le rôle de facteurs anatomiques et biomécaniques sur les traumatismes rachidiens

RESUME Les traumatismes a la colonne vertebrale (fractures osseuses, dechirures ligamentaires, hernies discales post-traumatiques, etc.) sont des lesions du systeme osteo-disco-ligamentaire qui portent souvent atteintes a l’integrite physique des victimes sur une longue duree et engendrent un fardeau economique enorme pour les victimes et les services de sante. Les chutes accidentelles et les accidents de la voie publique en sont les principales causes, etant responsables de plus de 85% des cas. Dans de tels accidents, la colonne vertebrale peut subir des efforts particulierement eleves dont l’intensite et la distribution dependent de facteurs anatomiques, qui sont propres a l’anatomie et difficilement modifiables (taille et forme des structures vertebrales, poids, âge et vieillissement, densite osseuse, architecture osseuse, etc.) et de facteurs biomecaniques, qui sont propres aux conditions dans lesquelles l’accident se produit (posture adoptee, severite et direction de l’impact, forces musculaires, etc.). Contrairement au segment cervical qui, au fil des ans, s’est merite une attention toute particuliere, la reponse biomecanique des segments lombaires et thoraciques (de T1 au sacrum) en situation accidentologique reste mal comprise. De fait, l’influence de facteurs anatomiques et biomecaniques tels que la presence d’osteophytes vertebraux (liee au vieillissement), le taux de chargement (lie a la severite de l’impact) et le profil sagittal rachidien (lie a la posture adoptee et defini par l’orientation et la forme de la colonne vertebrale dans le plan sagittal) sur les traumatismes de la colonne vertebrale T1-sacrum n’a pas ete etudiee de facon exhaustive. L’objectif general de ce projet doctoral etait d’etudier l’influence de ces facteurs sur les traumatismes de la colonne vertebrale en situation accidentologique. Trois questions de recherche ont ete etudiees : Q1 : Quelle est l’influence des osteophytes vertebraux sur le comportement biomecanique a la rupture de la colonne vertebrale ainsi que sur la typologie, le patron, la localisation et la prediction des fractures vertebrales en compression dynamique? Q2 : Quelle est l’influence du taux de chargement dynamique sur les traumatismes de la colonne vertebrale subis en compression, flexion, extension et cisaillement? ----------ABSTRACT Spinal injuries such as vertebral fractures, ligament tears and disc herniations are lesions of the osteo-disco-ligamentous system that violate the physical integrity of victims over long periods of time. These injuries create a great economic burden for both the injured and health services. The major causes of spinal injuries, being responsible for more than 85% of cases, are falls from a height and road accidents. In such situations, the spine can withstand very high loads. The intensity and distribution depend on many anatomical factors, specific to the anatomy of a given spine and difficult to change (size and shape of the vertebral structures, weight, age and ageing, bone density, bone architecture, etc.), and biomechanical factors, mainly driven by the conditions in which the accident occurs (adopted posture, impact velocity and direction, muscular forces, etc.). Unlike the cervical spine, which over the years has garnered growing interest, the biomechanical behavior of the thoracic and lumbar spines (from the T1 vertebra to the sacrum) under traumatic events remains unclear. Consequently, the influence of factors such as the presence of vertebral osteophytes (related to ageing), the loading rate (related to the impact velocity) and the sagittal profile of the spine (related to the adopted posture and defined by the orientation and shape of the spine in the sagittal plane) have not been thoroughly investigated. The overall objective of this research project was to study the influence of these intrinsic and extrinsic biomechanical factors on spinal injuries. Three research questions were asked: Q1: What is the influence of vertebral osteophytes on failure parameters, type, pattern, location and risk prediction of vertebral fractures when the spine is submitted to dynamic compression? Q2: What is the influence of the loading rate on spinal injuries when the spine is submitted to dynamic compression, flexion, extension and shear? Q3: What is the influence of the sagittal profile of the spine on spinal injuries sustained in accidents that involve compression and flexion-distraction mechanisms? To answer these research questions, experiments on human cadaveric spines were performed and a detailed biomechanical model of the spine was refined, validated against experimental data, and exploited.