Spine

Clinical problems of the human spine have a high prevalence, affecting more than 25.5 million people in 2012. Older adults, in particular, are susceptible to degenerative spine disorders such as deformities or osteoporosis. A basic requirement for proper management of various spinal disorders, effective injury prevention, and rehabilitation is a detailed knowledge of the fundamental biomechanics of the spine. Despite growing interest in biomechanical research on the spine during the last decades, however, many clinical problems remain largely unsolved, because of poor understanding of the underlying degeneration phenomena and the complexity of the spinal construct. In particular, diagnosis is challenging, because of the lack of tools to quantitatively assess soft tissue alteration, and because the most relevant clinical indices for diagnosis are not clearly established. Driven by ever-growing computer power and imaging devices, the development of FE models has become widespread, allowing scientists to overcome some of the existing shortcomings (invasiveness, complexity of the organization of the biological tissues, and complexity of establishing the loads present in the human spine, for example). These have emerged as powerful and reliable tools with considerable applications in surgery planning, in studying the etiology, progression, and effects of spinal deformities and intervertebral discs. These models have enhanced our understanding of the spine and will continue to do so. In our group, numerical work performed using FE modeling has highlighted the paramount influence of both geometric patient-specific modeling and in vivo personalization of tissue mechanical properties. Among the many exciting avenues for future research is the question of the validation of computational modeling and simulation with the perspective of supporting the development of medical devices

Contribution to FE modeling for intraoperative pedicle screw strength prediction

Although the use of pedicle screws is considered safe, mechanical issues still often occur. Commonly reported issues are screw loosening, screw bending and screw fracture. The aim of this study was to develop a Finite Element (FE) model for the study of pedicle screw biomechanics and for the prediction of the intraoperative pullout strength. The model includes both a parameterized screw model and a patient-specific vertebra model. Pullout experiments were performed on 30 human cadaveric vertebrae from ten donors. The experimental force-displacement data served to evaluate the FE model performance. μCT images were taken before and after screw insertion, allowing the creation of an accurate 3D-model and a precise representation of the mechanical properties of the bone. The experimental results revealed a significant positive correlation between bone mineral density (BMD) and pullout strength (Spearman ρ= 0.59, p< 0.001) as well as between BMD and pullout stiffness (Spearman ρ= 0.59, p< 0.001). A high positive correlation was also found between the pullout strength and stiffness (Spearman ρ = 0.84, p < 0.0001). The FE model was able to reproduce the linear part of the experimental force-displacement curve. Moreover, a high positive correlation was found between numerical and experimental pullout stiffness (Pearson ρ = 0.96, p< 0.005) and strength (Pearson ρ= 0.90, p< 0.05). Once fully validated, this model opens the way for a detailed study of pedicle screw biomechanics and for future adjustments of the screw design.The authors would like to thank Julie Choisne and Sylvain Persohn for their technical assistance. This study was supported by the ParisTech-BiomecAM chair program on subject-specific modeling, financed by Société Générale, Covea, Proteor and Fondation Cotrel

Modélisation Musculo-Squelettique Personnalisée du Rachis Cervical

Within the context of the scientific program chaired by BiomecAM, the musculoskeletal modelling of the cervical spine responds to various needs: understanding the damage mechanisms to this functional and essential structure, augmenting the efficiency level of pathology prevention, contributing to the design of new medical devices (orthoses or implants) and enabling orthopaedic and surgical treatment planning. Strong advancements have been made during the recent past years to evolve towards personalised modelling: innovative finite element mesh generation methods, in vivo quantitative analysis techniques to personalise the assignment of material properties to the intervertebral disc and the muscular system and preliminary models incorporating muscle activation have been developed.The aim of this PhD project is to exploit these scientific advancements to evolve towards a personalised musculoskeletal model of the intact, degenerated and instrumented cervical spine, thus contributing to the understanding of the degeneration mechanisms of the cervical spine and offering a means of orthopaedic and surgical treatment planning.Dans le cadre du programme scientifique de chaire BiomecAM, la modélisation musculo-squelettique du rachis cervical répond à différents besoins: comprendre les mécanismes d’endommagement de cette structure fonctionnelle essentielle, améliorer la prévention des pathologies, aider à la conception de nouveaux dispositifs (orthèses ou implants) et planification de traitements orthopédiques et chirurgicaux. De grandes avancées ont été faites ces dernières années pour progresser vers la modélisation personnalisée: des approches innovantes pour générer des maillages en éléments finis efficaces, des moyens d’analyse quantitative in vivo pour personnaliser les propriétés mécaniques du disque intervertébral et du système musculaire, des premières modélisations pertinentes de la commande neuro-motrice d’activation musculaire.L’objectif de cette thèse est de s’appuyer sur ces avancées pour proposer une modélisation musculo squelettique personnalisée du rachis cervical intact, lésé et restauré chirurgicalement, dans le but de mieux comprendre les mécanismes de dégénération du rachis cervical et d’évoluer vers un outil de planification de traitements orthopédiques et chirurgicaux s’appuyant sur cette modélisation personnalisée

THE SUBJECT-SPECIFIC MUSCULOSKELETAL MODELING OF THE CERVICAL SPINE

Dans le cadre du programme scientifique de chaire BiomecAM, la modélisation musculo-squelettique du rachis cervical répond à différents besoins: comprendre les mécanismes d’endommagement de cette structure fonctionnelle essentielle, améliorer la prévention des pathologies, aider à la conception de nouveaux dispositifs (orthèses ou implants) et planification de traitements orthopédiques et chirurgicaux. De grandes avancées ont été faites ces dernières années pour progresser vers la modélisation personnalisée: des approches innovantes pour générer des maillages en éléments finis efficaces, des moyens d’analyse quantitative in vivo pour personnaliser les propriétés mécaniques du disque intervertébral et du système musculaire, des premières modélisations pertinentes de la commande neuro-motrice d’activation musculaire.L’objectif de cette thèse est de s’appuyer sur ces avancées pour proposer une modélisation musculo squelettique personnalisée du rachis cervical intact, lésé et restauré chirurgicalement, dans le but de mieux comprendre les mécanismes de dégénération du rachis cervical et d’évoluer vers un outil de planification de traitements orthopédiques et chirurgicaux s’appuyant sur cette modélisation personnalisée.Within the context of the scientific program chaired by BiomecAM, the musculoskeletal modelling of the cervical spine responds to various needs: understanding the damage mechanisms to this functional and essential structure, augmenting the efficiency level of pathology prevention, contributing to the design of new medical devices (orthoses or implants) and enabling orthopaedic and surgical treatment planning. Strong advancements have been made during the recent past years to evolve towards personalised modelling: innovative finite element mesh generation methods, in vivo quantitative analysis techniques to personalise the assignment of material properties to the intervertebral disc and the muscular system and preliminary models incorporating muscle activation have been developed.The aim of this PhD project is to exploit these scientific advancements to evolve towards a personalised musculoskeletal model of the intact, degenerated and instrumented cervical spine, thus contributing to the understanding of the degeneration mechanisms of the cervical spine and offering a means of orthopaedic and surgical treatment planning

Characterisation of mechanical properties of human pulmonary and aortic tissue

The aim of this study is to characterise the mechanical properties of aortic and pulmonary arterial tissue, thereby comparing both tissue types and investigating the effect of lung-affecting disease on the mechanical behaviour of pulmonary arteries. Force-controlled, planar biaxial tensile tests were performed on human tissue samples collected from donors and receptors undergoing lung transplantation. In total 8 pulmonary donor, 6 pulmonary receptor and 6 aortic donor samples were tested and analysed. Donor samples are considered to be healthy, while receptors provided pathological tissue. The stiffness and strength of each sample were calculated from the stress-strain curves and a statistical analysis was performed between the three tissue groups (pulmonary donor, pulmonary receptor and aortic donor). The stiffness of aortic donor tissue was found to be significantly higher than for pulmonary donor tissue (p < 0.01) at physiological systolic stresses. The same could be observed for the strength (p < 0.05). Pulmonary samples were, however, significantly stiffer than aortic samples at stresses in the physiological range of aorta (p < 0.01). There was no significant difference found between the donors and receptors for pulmonary samples. The fact that the physiological pressure in the aorta is fivefold higher than in the pulmonary artery is also reflected in its stiffness and strength.status: publishe

A subject-specific biomechanical control model for the prediction of cervical spine muscle forces

Background: The aim of the present study is to propose a subject-specific biomechanical control model for theestimation of active cervical spine muscle forces.Methods: The proprioception-based regulation model developed by Pomero et al. (2004) for the lumbar spinewas adapted to the cervical spine. The model assumption is that the control strategy drives muscular activationto maintain the spinal joint load below the physiological threshold, thus avoiding excessive intervertebral displacements. Model evaluation was based on the comparison with the results of two reference studies. The effectof the uncertainty on the main model input parameters on the predicted force pattern was assessed. The feasibility of building this subject-specific model was illustrated with a case study of one subject.Findings: The model muscle force predictions, although independent from EMG recordings, were consistent withthe available literature, with mean differences of 20%. Spinal loads generally remained below the physiologicalthresholds. Moreover, the model behavior was found robust against the uncertainty on the muscle orientation,with a maximum coefficient of variation (CV) of 10%.Interpretation: After full validation, this model should offer a relevant and efficient tool for the biomechanicaland clinical study of the cervical spine, which might improve the understanding of cervical spine disorders

Burden and attitude to resistant and refractory migraine

Background: New treatments are currently offering new opportunities and challenges in clinical management and research in the migraine field. There is the need of homogenous criteria to identify candidates for treatment escalation as well as of reliable criteria to identify refractoriness to treatment. To overcome those issues, the European Headache Federation (EHF) issued a Consensus document to propose criteria to approach difficult-to-treat migraine patients in a standar