Mosnier, Thomas (2008) Contribution to spinal implants biomechanical analyisis and evaluation. PhD thesis Biomécanique, Laboratoire de Biomécanique, ENSAM 2008ENAM0046 p.180.

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Abstract

INTRODUCTION : Recent appearance of the first spinal implants, in the middle of the twentieth century, marks not only an acceleration of the development of spinal surgery, but also birth of a specific technology, which is yet only at its beginnings. How to evaluate these spinal implants, both at the time of their design and during surgery planning? Our research tasks were articulated around these issues.MATERIALS & METHODS : The first of our two axes of investigation relates to the normative evaluation in fatigue of spinal implants, and more particularly of osteosynthesis implants. We animated thus a work group, composed of implants manufacturers and researchers of the LBM, in order to propose a project of international standard defining methods for functional evaluation of spinal implants, taking into account the last scientific knowledge, particularly concerning the constraints undergone by spinal instrumentations in vivo. Our second axis of investigation relates to the biomechanical analysis, using numerical method, of the lumbar spine surgery. We worked for that on personalized geometrical and mechanical numerical model and finite elements simulation of the lumbar spine and its surgery. We have, within the framework of the Orthosim European project, contributed to make this tool evolve. Then, an extensive evaluation of the tool, as a help for surgical planning, was carried out. We finally carried out a preliminary evaluation of the influence of the operator on the answer of the tool and took part in its integration within the framework of an Internet website. RESULTS : The tests carried out according to the suggested protocol made it possible to highlight failure modes of the implants similar to those observed in vivo, confirming the functional aspect of the evaluation. Technical contents of the draft standard obtain a consensus from the ISO experts in September 2006. The final publication as an international standard is effective since April 2008. Then, the simulations tool was developed and improved, initially by making the process reliable, then by widening the panel of the surgery options available. The retrospective evaluation confirmed the predictive aspect of simulations, regarding the influence of a given surgical strategy on the clinical result. Lastly, the provision of the clinicians of the simulations tool was committed. CONCLUSION : This work enabled us to contribute, on the one hand to the evolution of standards for spinal implants evaluation, with a more biomechanical dimension, and on the other hand to take part in installation of an innovating tool, based on numerical simulations, for surgery planning and biomechanical analysis of the lumbar spine surgery

Table of content

Introduction Générale ___________________________________________ 11

1ère partie: Le rachis lombaire - Pathologies associées - Chirurgie ________ 15

1. Anatomie descriptive du rachis lombaire ________________________________ 15

1.1. Les plans de référence _____________________________________________ 15

1.2. La Colonne vertébrale _____________________________________________ 16

1.3. Le Rachis lombo-sacré _____________________________________________ 17

1.4. Les articulations intervertébrales ______________________________________ 19

2. Anatomie fonctionnelle du rachis lombaire ______________________________ 21

2.1. Mobilités articulaires du rachis lombaire ________________________________ 21

2.2. Les efforts appliqués au rachis dorso-lombaire ___________________________ 25

3. Les pathologies lombaires _____________________________________________ 28

3.1. L'instabilité vertébrale ______________________________________________ 28

3.2. Pathologies dégénératives ___________________________________________ 29

3.3. Ostéoporose _____________________________________________________ 31

3.4. Lésions traumatiques ______________________________________________ 31

4. La chirurgie du rachis lombaire _______________________________________ 32

4.1. Les voies d’abord _________________________________________________ 32

4.2. Les résections ou libérations _________________________________________ 32

4.3. L'arthrodèse _____________________________________________________ 34

4.4. L'ostéosynthèse __________________________________________________ 34

4.5. La restauration fonctionnelle ________________________________________ 35

4.6. Les complications post-opératoires ____________________________________ 36

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2nde Partie : Les implants d’osteosynthèse rachidienne et leur évaluation __ 39

1. Les implants rachidiens ______________________________________________ 39

1.1. Introduction _____________________________________________________ 39

1.2. Les systèmes d'ostéosynthèse ________________________________________ 39

2. Evaluation des Implants rachidiens _____________________________________ 42

2.1. Les différents types d’évaluation ______________________________________ 42

2.2. Evaluation in vivo _________________________________________________ 43

2.3. Evaluation expérimentale in vitro ______________________________________ 46

2.4. Moyens d'évaluation numériques _____________________________________ 49

2.5. l'Evaluation mécanique pré-clinique ___________________________________ 53

2.6. Perspectives d’évaluation des implants rachidiens et axes d’investigations _______ 57

3eme Partie : Evaluation Mécanique pré-clinique « fonctionnelle » des

implants rachidiens _____________________________________________ 59

1. Contexte de développement d'une norme d’évaluation des implants rachidiens 59

1.1. Génèse du projet _________________________________________________ 59

1.2. Le cadre normatif _________________________________________________ 59

1.3. Mise en place d’un Nouveau thème de travail ____________________________ 60

2. Matériel & Méthode _________________________________________________ 61

2.1. Principe de la méthode d’essais proposée _______________________________ 61

2.2. Cahier des charges du support d'essai pour l'évaluation fonctionnelle __________ 61

2.3. Définition du support d'essai ________________________________________ 63

2.4. Définition du chargement pour l'évaluation fonctionnelle___________________ 70

2.5. Evaluation numérique de la solution proposée ___________________________ 71

2.6. Evaluation d'implants suivant le protocole défini _________________________ 74

3. Résultats & discussion _______________________________________________ 75

3.1. Evaluation numérique de la solution proposée ___________________________ 75

3.2. Essais menés suivant le protocole proposé ______________________________ 80

4. Conclusion _________________________________________________________ 84

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