Étude biomécanique de la spondylolyse et du spondylolisthésis chez l'enfant : étude de cas

Anatomie descriptive et fonctionnelle et aspects biomécaniques du tronc -- Le spondylolisthésis -- Revue des différentes approches de modélisation par éléments finis du spondylolisthésis -- Méthodes de modélisation développées à l'École Polytechnique de Montréal et au CHU Sainte-Justine -- Problématique, hypothèses et objectifs -- Biomechanical evaluation of pediatric low-grade isthmic spondylolisthesis using a personalized finite element model -- Discussion complémentaire de l'article -- Aspects méthodologiques -- Résultats

Biomechanical evaluation of predictive parameters of progression in adolescent isthmic spondylolisthesis: a computer modeling and simulation study

<p>Abstract</p> <p>Background</p> <p>Pelvic incidence, sacral slope and slip percentage have been shown to be important predicting factors for assessing the risk of progression of low- and high-grade spondylolisthesis. Biomechanical factors, which affect the stress distribution and the mechanisms involved in the vertebral slippage, may also influence the risk of progression, but they are still not well known. The objective was to biomechanically evaluate how geometric sacral parameters influence shear and normal stress at the lumbosacral junction in spondylolisthesis.</p> <p>Methods</p> <p>A finite element model of a low-grade L5-S1 spondylolisthesis was constructed, including the morphology of the spine, pelvis and rib cage based on measurements from biplanar radiographs of a patient. Variations provided on this model aimed to study the effects on low grade spondylolisthesis as well as reproduce high grade spondylolisthesis. Normal and shear stresses at the lumbosacral junction were analyzed under various pelvic incidences, sacral slopes and slip percentages. Their influence on progression risk was statistically analyzed using a one-way analysis of variance.</p> <p>Results</p> <p>Stresses were mainly concentrated on the growth plate of S1, on the intervertebral disc of L5-S1, and ahead the sacral dome for low grade spondylolisthesis. For high grade spondylolisthesis, more important compression and shear stresses were seen in the anterior part of the growth plate and disc as compared to the lateral and posterior areas. Stress magnitudes over this area increased with slip percentage, sacral slope and pelvic incidence. Strong correlations were found between pelvic incidence and the resulting compression and shear stresses in the growth plate and intervertebral disc at the L5-S1 junction.</p> <p>Conclusions</p> <p>Progression of the slippage is mostly affected by a movement and an increase of stresses at the lumbosacral junction in accordance with spino-pelvic parameters. The statistical results provide evidence that pelvic incidence is a predictive parameter to determine progression in isthmic spondylolisthesis.</p

Relantionship between the feedstock powders reactivity and the Electrochemical properties of 316L Stainless steel obtained by laser powder bed fusion

International audience3D printing by Laser-Powder Bed Fusion (L-PBF) is an innovative process using a high energy density laser to melt the raw material into a powder form. Previous studies have shown that the powder properties are crucial for the density, quality and microstructure of the materials produced [1, 2] but much remains unknown about their influence on corrosion behaviour. Therefore, the objective of this study is to establish the relationship between electrochemical reactivity of the raw material and the additively manufactured 316L stainless steel (SS). To this aim, cyclic voltammetry technique was performed using a cavity microelectrode (CME) densely filled with metal 316L powder (Fig. 1. A and B) and a sessile drop over the surface of L-PBF 316L SS (Fig. 2) in H2SO4 (0.5 mol.L-1) at room temperature. These configurations allow the use of small amounts of material, the reduction of the electrode size and consequently, smaller ohmic drop [3]. As a result, high-scan rate cyclic voltammetry can be applied, allowing faster measurements. In addition, the electrochemical droplet cell is of great interest to study corrosion processes of heterogeneous materials. The principle consists in placing directly a sessile drop of a few microliters on the material surface considered as the working electrode. By this way, the current and potential lines are limited to the small volume of the hemispherical cap. For a few microliter drop, the diameter of the covered surface is of the order of a millimetre and depends on the wettability of the material [4]. To complete the experimental setup, the reference electrode and the counter electrode are introduced inside the sessile drop (Fig. 1. C).Cyclic voltammetry measurements showed similar electrochemical reactivity between the metal powder and L-PBF 316L SS. Several analytical techniques were also used for the characterizations of powders and materials in order to explain the relationship between them (chemical composition and heterogeneities, precipitates, etc.)

FPGA-Based HD Camera System for the Micropositioning of Biomedical Micro-Objects Using a Contactless Micro-Conveyor

With recent advancements, micro-object contactless conveyers are becoming an essential part of the biomedical sector. They help avoid any infection and damage that can occur due to external contact. In this context, a smart micro-conveyor is devised. It is a Field Programmable Gate Array (FPGA)-based system that employs a smart surface for conveyance along with an OmniVision complementary metal-oxide-semiconductor (CMOS) HD camera for micro-object position detection and tracking. A specific FPGA-based hardware design and VHSIC (Very High Speed Integrated Circuit) Hardware Description Language (VHDL) implementation are realized. It is done without employing any Nios processor or System on a Programmable Chip (SOPC) builder based Central Processing Unit (CPU) core. It keeps the system efficient in terms of resource utilization and power consumption. The micro-object positioning status is captured with an embedded FPGA-based camera driver and it is communicated to the Image Processing, Decision Making and Command (IPDC) module. The IPDC is programmed in C++ and can run on a Personal Computer (PC) or on any appropriate embedded system. The IPDC decisions are sent back to the FPGA, which pilots the smart surface accordingly. In this way, an automated closed-loop system is employed to convey the micro-object towards a desired location. The devised system architecture and implementation principle is described. Its functionality is also verified. Results have confirmed the proper functionality of the developed system, along with its outperformance compared to other solutions