Comparative study of intraoperative knee flexion with three different TKR designs

SummaryIntroductionSubstantial flexion after total knee arthroplasty (TKA) is required for certain categories of patients who wish to squat or kneel in their daily life. Many factors influence this postoperative flexion, including the prosthesis design. It is therefore valuable to in vivo analyze these factors on three knee prosthesis designs through a study of their intraoperative flexion.HypothesisThe posterior-stabilized (PS) knee prostheses provide better intraoperative flexion than the ultracongruent (UC) model. Of the currently available PS models, the high-flexion ones have better intraoperative flexion than standard models. Our main focus endpoint was the intraoperative flexion achieved, before soft-tissues closure, during TKA surgical procedure.Patients and methodsThis was a controlled study. Seventy-two osteoarthritic knees requiring TKA were included to compare three selected prosthesis models: the SAL ultracongruent and two PS models (the standard LPS and the LPS Flex). This was a single-operator study, with patients divided into three homogenous, comparable groups, in which intraoperative measurement of flexion was performed using computer-assisted navigation. Statistical analysis allowed comparison of the three models.ResultsIntraoperatively, after prosthesis implantation, before soft-tissues closure, the mean flexion of the LPS-Flex was 134° versus 124° for the SAL (p=0.0004); the mean flexion of the standard LPS model was 130° versus 124° for the SAL (p=0.14); the PS Flex model showed no significant difference (p=0.26) in flexion (134°) compared to the standard model (130°). The SAL ultracongruent model seemed to be a factor reducing the intraoperative flexion by 8° compared to the PS models (p<10−4).DiscussionIn this study, the PS designs (standard or Flex) provided better intraoperative flexion than the SAL ultracongruent design. However, the LPS Prosthesis did not demonstrate superiority over the standard LPS Prosthesis.Level of evidenceLevel III, low-power prospective study

Un modèle d'interaction réaliste pour la simulation de marchés financiers

Dans les modèles de marché multi-agents utilisés habituellement, la structure du marché est presque toujours réduite à une équation qui aggrège les décisions des agents de façon synchrone pour mettre à jour le prix de l'action à chaque pas de temps. Sur les marchés réels, ce processus est totalement différent : le prix de l'action émerge d'interactions survenant de manière asynchrone entre les acheteurs et les vendeurs. Dans cet article, nous introduisons un modèle de marché artificiel conçu pour être le plus proche possible de la structure des marchés réels. Ce modèle est basé sur un carnet d'ordres à travers lequel les agents échangent des actions de manière asynchrone. Nous montrons que, sans émettre d'hypothèses particulières sur le comportement des agents, ce modèle exhibe de nombreuses propriétés statistiques des marchés réels. Nous soutenons que la plupart de ces propriétés proviennent de la manière dont les agents interagissent plutôt que de leurs comportements. Ce résutat expérimental est validé et renforcé grâce à l'utilisation de nombreux tests statistiques utilisés par les économistes pour caractériser les propriétés des marchés réels. Nous finissons par quelques perspectives ouvertes par les avantages de l'utilisation de tels modèles pour le développement, le test et la validation d'automates d'investissement. In usual multi-agent stock market models, market structure is mostly reduced to an equation matching supply and demand, which synchronously aggregates agents decisions to update stock price at each time steps. On real markets, the process is however very different: stock price emerges from one-to one asynchronous interactions between buyers and sellers at various time step. In this article, we introduce an artificial stock market model designed to be close to real market structure. The model is based on a centralized orderbook through which agents exchange stocks asynchronously.We show that, without making any strong assumption on agents behaviors, this model exhibits many statistical properties of real stock markets. We argue that most of market features are implied by the exchange process more than by agents behaviors. This experimental result is validated and strengthen using several tests used by economists to characterize real market. We finally put in perspective the advantages of such a realistic model to develop, test and validate behavior of automated trading agents

Rotational positioning of the tibial tray in total knee arthroplasty: A CT evaluation

SummaryIntroductionVarious surgical techniques have been described to set the rotational alignment of the tibial baseplate during total knee arthroplasty. The self-positioning method (“self-adjustment”) aligns the tibial implant according to the rotational alignment of the femoral component which is used as a reference after performing repeated knee flexion/extension cycles. Postoperative computed tomography scanning produces accurate measurements of the tibial baseplate rotational alignment with respect to the femoral component.HypothesisThe rotational positioning of the tibial baseplate matches the rotation of the femoral component with parallel alignment to the prosthetic posterior bicondylar axis.Patients and methodsA 3-month follow-up CT scan was carried out after primary total knee arthroplasty implanted in osteoarthritic patients with a mean 7.8° varus deformity of the knee in 50 cases and a mean 8.7° valgus deformity of the knee in 44 cases. The NexGen LPS Flex (Zimmer) fixed-bearing knee prosthesis was used in all cases. An independant examiner (not part of the operating team) measured different variables: the angle between the anatomic transepicondylar axis and the posterior bicondylar axis of the femoral prosthesis (prosthetic posterior condylar angle), the angle between the posterior bicondylar axis and the posterior marginal axis of the tibial prosthesis, the angle between the posterior marginal axis of the tibial prosthesis and the posterior marginal axis of the tibial bone and finally the angle between the anatomic transepicondylar axis and the posterior marginal axis of the tibial prosthesis.ResultsFor the genu varum and genu valgum subgroups, the mean posterior condylar axis of the femoral prosthesis was 3.1° (SD: 1.91; extremes 0° to 17.5°) and 4.7° (SD: 2.7; extremes 0° to 11°) respectively. The tibial baseplate was placed in external rotation with respect to the femoral component: 0.7° (SD : 4.45; extremes –9.5° to 9.8°) and 0.9° (SD: 4.53; extremes –10.8° to 9.5°), but also to the native tibia: 6.1° (SD: 5.85; extremes –4.6° to 22.5°) and 12.5° (SD: 8.6; extremes –10° to 28.9°). The tibial component was placed in internal rotation relative to the anatomic transepicondylar axis: 1.9° (SD : 4.93; extremes –13.6° to 7°) and 3° (SD : 4.38; extremes –16.2° to 4.8°).DiscussionThe tibial component is aligned parallel to the femoral component whatever the initial frontal deformity (P≅0.7). However, a difference was observed between the rotational alignment of the tibial baseplate and the native tibia depending on the initial deformity and could be attributed to the morphological variations of the bony tibial plateau in case of genu valgum.ConclusionThe self-positioning method is a reproducible option when using this type of implant since it allows the tibial component to be positioned parallel to the posterior border of the femur.Level of evidenceLevel III. Observational prospective study

Control of dipolar relaxation in external fields

We study dipolar relaxation in both ultra-cold thermal and Bose-condensed chromium atom gases. We show three different ways to control dipolar relaxation, making use of either a static magnetic field, an oscillatory magnetic field, or an optical lattice to reduce the dimensionality of the gas from 3D to 2D. Although dipolar relaxation generally increases as a function of a static magnetic field intensity, we find a range of non-zero magnetic field intensities where dipolar relaxation is strongly reduced. We use this resonant reduction to accurately determine the S=6 scattering length of chromium atoms: $a_6 = 103 \pm 4 a_0$. We compare this new measurement to another new determination of $a_6$, which we perform by analysing the precise spectroscopy of a Feshbach resonance in d-wave collisions, yielding $a_6 = 102.5 \pm 0.4 a_0$. These two measurements provide by far the most precise determination of $a_6$ to date. We then show that, although dipolar interactions are long-range interactions, dipolar relaxation only involves the incoming partial wave $l=0$ for large enough magnetic field intensities, which has interesting consequences on the stability of dipolar Fermi gases. We then study ultra-cold chromium gases in a 1D optical lattice resulting in a collection of independent 2D gases. We show that dipolar relaxation is modified when the atoms collide in reduced dimensionality at low magnetic field intensities, and that the corresponding dipolar relaxation rate parameter is reduced by a factor up to 7 compared to the 3D case. Finally, we study dipolar relaxation in presence of radio-frequency (rf) oscillating magnetic fields, and we show that both the output channel energy and the transition amplitude can be controlled by means of rf frequency and Rabi frequency.Comment: 25 pages, 17 figure

Stability of dark solitons in three dimensional dipolar Bose-Einstein condensates

The dynamical stability of dark solitons in dipolar Bose-Einstein condensates is studied. For standard short-range interacting condensates dark solitons are unstable against transverse excitations in two and three dimensions. On the contrary, due to its non local character, the dipolar interaction allows for stable 3D stationary dark solitons, opening a qualitatively novel scenario in nonlinear atom optics. We discuss in detail the conditions to achieve this stability, which demand the use of an additional optical lattice, and the stability regimes.Comment: 4 pages, 3 eps figure

CARIOQA: Definition of a Quantum Pathfinder Mission

A strong potential gain for space applications is expected from the anticipated performances of inertial sensors based on cold atom interferometry (CAI) that measure the acceleration of freely falling independent atoms by manipulating them with laser light. In this context, CNES and its partners initiated a phase 0 study, called CARIOQA, in order to develop a Quantum Pathfinder Mission unlocking key features of atom interferometry for space and paving the way for future ambitious space missions utilizing this technology. As a cornerstone for the implementation of quantum sensors in space, the CARIOQA phase 0 aimed at defining the Quantum Pathfinder Mission's scenario and associated performance objectives. To comply with these objectives, the payload architecture has been designed to achieve long interrogation time and active rotation compensation on a BEC-based atom interferometer. A study of the satellite architecture, including all the subsystems, has been conducted. Several technical solutions for propulsion and attitude control have been investigated in order to guarantee optimal operating conditions (limitation of micro-vibrations, maximization of measurement time). A preliminary design of the satellite platform was performed.Comment: Proceedings of International Conference on Space Optics (ICSO) 2022; 3-7 October 2022; Dubrovnik; Croati

Complex lithium ion dynamics in simulated LiPO3 glass studied by means of multi-time correlation functions

Molecular dynamics simulations are performed to study the lithium jumps in LiPO3 glass. In particular, we calculate higher-order correlation functions that probe the positions of single lithium ions at several times. Three-time correlation functions show that the non-exponential relaxation of the lithium ions results from both correlated back-and-forth jumps and the existence of dynamical heterogeneities, i.e., the presence of a broad distribution of jump rates. A quantitative analysis yields that the contribution of the dynamical heterogeneities to the non-exponential depopulation of the lithium sites increases upon cooling. Further, correlated back-and-forth jumps between neighboring sites are observed for the fast ions of the distribution, but not for the slow ions and, hence, the back-jump probability depends on the dynamical state. Four-time correlation functions indicate that an exchange between fast and slow ions takes place on the timescale of the jumps themselves, i.e., the dynamical heterogeneities are short-lived. Hence, sites featuring fast and slow lithium dynamics, respectively, are intimately mixed. In addition, a backward correlation beyond the first neighbor shell for highly mobile ions and the presence of long-range dynamical heterogeneities suggest that fast ion migration occurs along preferential pathways in the glassy matrix. In the melt, we find no evidence for correlated back-and-forth motions and dynamical heterogeneities on the length scale of the next-neighbor distance.Comment: 12 pages, 13 figure