Étude biomécanique des mécanismes de progression du spondylolisthésis.

RÉSUMÉ Le spondylolisthésis se définit par un glissement postéro-antérieur d’une vertèbre par rapport à sa sous-jacente. Cette pathologie se développe dans la plupart des cas après une spondylolyse, soit une rupture de la pars interarticulaire de la vertèbre, ou d’une dysplasie importante de ses éléments postérieurs. Le spondylolisthésis affecte environ 6% de la population et apparaît le plus souvent à la jonction lombosacrée (L5-S1). Dans la littérature, on identifie plusieurs sévérités de spondylolisthésis : les spondylolisthésis bas grade (grades 1 et 2), qui comprennent entre autres les types « shear » et « nutcracker », qui se différencient suivant les valeurs de l’incidence pelvienne (PI) et de la pente sacrée (SS) et les spondylolisthésis haut grade (grades 3 à 5) comprenant les types « bassin balancé » et « bassin rétroversé » qui se différencient suivant les valeurs de la pente sacrée et du tilt pelvien (PT). Dans la littérature, la progression du spondylolisthésis est habituellement documentée et analysée au moyen de mesures géométriques (incidence pelvienne, pente sacrée, tilt pelvien) sans prendre en considération leurs effets et leurs actions biomécaniques sur cette progression. C’est pourquoi les relations entre paramètres et forces en jeu dans le risque de progression de la pathologie ne sont pas bien connues. Ainsi, le but du projet était de développer un modèle par éléments finis (MEF) paramétrable d’un rachis----------ABSTRACT Spondylolisthesis is a postero-anterior slippage of a vertebra with respect to its inferior vertebra. This pathology mainly occurs after a spondylolysis, which is a stress fracture of the pars interarticularis of the vertebrae, or after a high dysplasia of its posterior bony elements. Spondylolisthesis affects about 6% of the population and usually occurs at the lumbosacral junction (L5-S1). There exists different severities of spondylolisthesis: lowgrade spondylolisthesis (grades 1 and 2), including the “shear-type” and “nutcrackertype”, which differ in pelvic incidence (PI) and sacral slope (SS) values, and high-grade spondylolisthesis (grade 3 to 5), including “balanced pelvis”-type and “retroverted pelvis”-type, which differ in sacral slope and pelvic tilt (PT) values. The progression of spondylolisthesis is usually documented and analyzed using geometric measurements (PI, SS, PT) without taking their effects and their biomechanical actions into account. That is why the link between the predicting parameters and the forces responsible for the progression of the pathology is poorly documented in the literature. The aim of this project was to develop a parametric finite element model (FEM) of a paediatric spine to analyze the conditions involved in the risk of progression of the pathology and to test the hypothesis that pelvic incidence is a predictive parameter of the deformity. This model includes the spondylolysis and sacral dome, and can be personalized depending on the type of spondylolisthesis. A detailed biomechanica

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