Étude biomécanique par éléments finis de dispositifs d'arthrodèse de la jonction sacro-iliaque

RÉSUMÉ Les douleurs au dos sont un problème de santé publique majeur. En effet, c'est la deuxième cause la plus fréquente de consultation d'un médecin. La jonction sacro-iliaque est reconnue comme étant une des sources de ces douleurs dans 10 à 30% des cas. Les pathologies qui en sont responsables sont principalement dégénératives (sacro-ilites). Après échec de méthodes plus conservatives (physiothérapie, dénervation, infiltration), l'arthrodèse de la jonction sacro-iliaque est le dernier recours de traitement pour les patients souffrant de telles pathologies. Cette procédure vise à réduire les déplacements intra-articulaires pour permettre à l’os de se former entre les deux facettes de l’articulation afin de la rigidifier entièrement. Plus ces déplacements sont faibles, meilleure et plus rapide sera l’arthrodèse. Traditionnellement, cette chirurgie était pratiquée de manière ouverte, et donc invasive, ce qui rendait peu de patients éligibles à une telle procédure. Cependant, depuis une dizaine d'années, de nouveaux types de dispositifs d'arthrodèse sont apparus. Ils sont canulés afin de permettre une chirurgie percutanée, beaucoup moins invasive, ce qui tend à la rendre plus accessible. Leur surface et leur forme ont également été conçues pour favoriser la croissance osseuse et l’ostéointégration du dispositif. La jonction sacro-iliaque est une articulation complexe, comportant à la fois des caractéristiques d’une diarthrose (présence de cartilage hyalin) dans sa partie proximale et d’une synarthrose (présence de fibrocartilage) dans sa partie distale. Ses déplacements sont très limités, quelques millimètres en translation et quelques degrés en rotation, ce qui les rend difficiles à caractériser et mesurer. Ceci est accentué par sa position profonde qui complique son accès et son observation, même avec les techniques d’imagerie les plus récentes. Elle assure la transmission des forces entre la partie supérieure du corps et les membres inférieurs, et supporte donc des efforts importants. En cas de dysfonctionnement de la jonction sacro-iliaque (JSI), ses mouvements se révèlent particulièrement douloureux, ce qui nécessite finalement la fusion de l’articulation. Peu d’études biomécaniques sont à la disposition des chirurgiens pour juger de l'action et de l'efficacité des implants à fusionner l'articulation. À court et moyen termes, l’os n’ayant pas encore pu se développer entre les surfaces condylaires, la réduction du déplacement est entièrement assurée par l’implant, dont les effets sont encore méconnus.----------ABSTRACT Low back pain (LBP) is a major public health concern. Indeed, it is the second most frequent reason patients consult a physician. The sacroiliac joint (SIJ) is a known pain generator, affecting 10 to 30% of patients suffering chronic LBP, with pathologies such as degenerative sacroiliitis or sacroiliac joint disruption. After conservative treatment (physiotherapy, denervation, injections) failure, SIJ arthrodesis is the last resort. The main objective of this procedure is to reduce the intra-articular displacements in order to allow bone ingrowth between the two condylar surfaces and, eventually, fuse the articulation. The lower those displacements are, the better the arthrodesis is. Traditionally, this surgery was performed using an open procedure which was invasive and for which few patients were eligible. The last decade has seen the advent of new kinds of SIJ fusion devices. As they are cannulated, they allow percutaneous minimally invasive surgeries accessible to a larger number of patients. Their surface and shape are designed to promote bone ingrowth and thus improve the device osseointegration. The SIJ is a complex articulation. It has characteristics of both a diarthrosis (hyaline cartilage) in its proximal part and a synarthrosis (fibrocartilage) in its distal part. SIJ displacements are small (a few millimeters in translation and a few degrees in rotation) which render their measurement and characterization problematic. The SIJ deep location makes it even harder by complicating its access and observation despite the most recent imaging techniques. The sacroiliac joint transmits upper body weight to the lower limbs and thus endures heavy loads. In case of disruptions, SIJ motions are painful and ultimately require an arthrodesis. Currently, surgeons rely on few biomechanical studies to assess the device ability to perform an arthrodesis. At short and mid-terms, the implants alone ensure the SIJ stabilization since the bone growth cannot actually fuse the articulation yet. However the biomechanics of the instrumentation is quite unknown and the published data is sparse. The objective of this project was to assess the SIJ instrumentation effects on the intra-articular displacements using a comprehensive finite element model (FEM) of the pelvis. The tested hypothesis is that the SIJ instrumentation is able to reduce by more than 50% the articular motions and that the instrumentation parameters have a significant (>10%) influence on one configuration ability to reduce the SIJ displacements

Computational Techniques to Predict Orthopaedic Implant Alignment and Fit in Bone

Among the broad palette of surgical techniques employed in the current orthopaedic practice, joint replacement represents one of the most difficult and costliest surgical procedures. While numerous recent advances suggest that computer assistance can dramatically improve the precision and long term outcomes of joint arthroplasty even in the hands of experienced surgeons, many of the joint replacement protocols continue to rely almost exclusively on an empirical basis that often entail a succession of trial and error maneuvers that can only be performed intraoperatively. Although the surgeon is generally unable to accurately and reliably predict a priori what the final malalignment will be or even what implant size should be used for a certain patient, the overarching goal of all arthroplastic procedures is to ensure that an appropriate match exists between the native and prosthetic axes of the articulation. To address this relative lack of knowledge, the main objective of this thesis was to develop a comprehensive library of numerical techniques capable to: 1) accurately reconstruct the outer and inner geometry of the bone to be implanted; 2) determine the location of the native articular axis to be replicated by the implant; 3) assess the insertability of a certain implant within the endosteal canal of the bone to be implanted; 4) propose customized implant geometries capable to ensure minimal malalignments between native and prosthetic axes. The accuracy of the developed algorithms was validated through comparisons performed against conventional methods involving either contact-acquired data or navigated implantation approaches, while various customized implant designs proposed were tested with an original numerical implantation method. It is anticipated that the proposed computer-based approaches will eliminate or at least diminish the need for undesirable trial and error implantation procedures in a sense that present error-prone intraoperative implant insertion decisions will be at least augmented if not even replaced by optimal computer-based solutions to offer reliable virtual “previews” of the future surgical procedure. While the entire thesis is focused on the elbow as the most challenging joint replacement surgery, many of the developed approaches are equally applicable to other upper or lower limb articulations