ParisTech

About: ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Residual stress & Finite element method. The organization has 1888 authors who have published 1965 publications receiving 55532 citations. The organization is also known as: Paris Institute of Technology & ParisTech Développement.

Three-dimensional finite element analysis of shallow indentation of rough strain-hardening surface

Abstract: Three-dimensional finite element modeling of the contact between a rigid spherical indenter and a rough surface is presented when considering both the loading and unloading phases. The relationships among the indentation load, displacement, contact area, and mean contact pressure for both loading and unloading are established through a curve fitting using sigmoid logistic and power law functions. The contact load is proportional to the contact area, and the mean contact pressure is related to the characteristic stress, which is dependent on the material properties. The residual displacement is proportional to the maximum indentation displacement. A proportional relationship also exists for plastically dissipated energy and work conducted during loading. The surface roughness results in an effective elastic modulus calculated from an initial unloading stiffness several times larger than the true value of elastic modulus. Nonetheless, the calculated modulus under a shallow spherical indentation can still be applied for a relative comparison.

The global alignment in patients with lumbar spinal stenosis: our experience using the EOS full-body images.

Abstract: Lumbar stenosis is frequently observed and treated by spine surgeons. The extent of neurological decompression and the potential spinal fixation are the basic concerns when surgery is planned. But this segmented approach to the problem is sometimes insufficient due to the complex functional situations induced by a sagittal imbalance of the patient and the combination of pathologies known as hip-spine or knee-spine syndromes. A total of 373 consecutive patients included from our EOS and clinical data base. Patients were divided in two groups. Group A included patients presenting exclusive spinal issues (172 cases) out of whom 117 (68 %) had sagittal imbalance. Among 201 patients with associated lower limbs issues (group B), 122 (61 %) had sagittal imbalance. The perception of imbalance was noticed in 54 % (93 cases) in group A and 57 % (115 cases) in group B. In the global series of 239 imbalanced cases, the key point was a spine issue for 165 patients (the 117 patients with only spine problems and 48/122 cases with combined spine and lower limbs problems). But in the patients with combined spine and lower limbs problems, we individualized hip-spine syndromes (24/122 patients) and knee-spine syndromes (13/122 patients). In some cases, (37/122 patients) the anatomical and functional situations were more complex to characterize a spine-hip or a hip-spine problem. The EOS full-body images provide new information regarding the global spinal and lower limbs alignment to improve the understanding of the patient functional posture. This study highlights the importance of the lower limb evaluation not only as compensatory mechanism of the spinal problems but also as an individualized parameter with its own influence on the global balance analysis. Level of evidence IV diagnostic case series.