Water, oceanic fracture zones and the lubrication of subducting plate boundaries - insights from seismicity

We investigate the relationship between subduction processes and related seismicity for the Lesser Antilles Arc using the Gutenberg-Richter law. This power lawdescribes the earthquakemagnitude distribution, with the gradient of the cumulative magnitude distribution being commonly known as the b-value. The Lesser Antilles Arc was chosen because of its alongstrike variability in sediment subduction and the transition from subduction to strike-slip movement towards its northern and southern ends. The data are derived from the seismicity catalogues from the Seismic Research Centre of The University of the West Indies and the Observatoires Volcanologiques et Sismologiques of the Institut de Physique du Globe de Paris and consist of subcrustal events primarily from the slab interface. The b-value is found using a Kolmogorov-Smirnov test for a maximum-likelihood straight line-fitting routine. We investigate spatial variations in b-values using a grid-search with circular cells as well as an along-arc projection. Tests with different algorithms and the two independent earthquake cataloges provide confidence in the robustness of our results. We observe a strong spatial variability of the b-value that cannot be explained by the uncertainties. Rather than obtaining a simple north-south b-value distribution suggestive of the dominant control on earthquake triggering being water released from the sedimentary cover on the incoming American Plates, or a b-value distribution that correlates with on the obliquity of subduction, we obtain a series of discrete, high b-value 'bull's-eyes' along strike. These bull's-eyes, which indicate stress release through a higher fraction of small earthquakes, coincide with the locations of known incoming oceanic fracture zones on the American Plates. We interpret the results in terms of water being delivered to the Lesser Antilles subduction zone in the vicinity of fracture zones providing lubrication and thus changing the character of the related seismicity. Our results suggest serpentinization around mid-ocean ridge transform faults, which go on to become fracture zones on the incoming plate, plays a significant role in the delivery of water into the mantle at subduction zones

Discussing the Role of Classification Algorithms in Clinical Predictions with help of Case Studies

This paper discuss about the important role of classification algorithms in clinical predictions , two case studies one for breast cancer and other for heart disease prediction with help of classification data mining techniques is presented in this paper. Online freely accessible data is used for the said case studies. Used data is publicly available data on internet consisting of 909 records for heart disease and 699 for breast cancer. C4.5 and the C5.0 Two well-known decision tree algorithms used to get the rules for predictions, and these rules used for improving the quality of an open source Pathology Management System based on Care2x.Performances of these algorithms are also compared. This Paper will further discuss about the importance of open source software in healthcare as well as how a pathology management system can adopt Evidence Based Medicine (EBM). EBM is a new and important approach which can greatly improve decision making in health care. EBM's task is to prevent, diagnose and medicate diseases using medical evidence [5].Clinical decisions must be based on scientific evidence that demonstrates effectiveness. This paper is basically extension of our previous work ‘A Prototype of Cancer/Heart Disease Prediction Model Using Data Mining’

Réduire ou ralentir la fibrillation auriculaire : est-ce la bonne question en 2010 ?

RésuméPourquoi et comment traiter la fibrillation atriale ? Cette question a paru simple pendant de nombreuses années : la fibrillation atriale, trouble du rythme cardiaque, doit être traitée par des médicaments anti-arythmiques, tant qu’ils peuvent être efficaces. Les effets secondaires de ces médicaments, comme le bénéfice fréquemment apporté par un simple traitement bradycardisant a amené à discuter il y a une dizaine d’années deux stratégies thérapeutiques, réduire ou ralentir. Mais ce choix largement mis en avant dans les précédentes recommandations thérapeutiques, apparaît aujourd’hui réducteur. En 2010 on peut sans doute proposer deux objectifs thérapeutiques, traiter les symptômes et traiter le risque cardiovasculaire associée à la fibrillation. La gêne symptomatique entraînée par l’arythmie doit être toujours évaluée chez nos patients, volontiers selon la classification récente EHRA. Parallèlement la fibrillation fait partie du continuum cardiovasculaire, et constitue un marqueur de risque supplémentaire : il apparaît certain que le contrôle de ce risque supplémentaire associé à la fibrillation ne dépend pas uniquement du traitement de l’arythmie proprement dite.SummaryWhy and how to treat atrial fibrillation? This question seemed simple for many years: atrial fibrillation, a cardiac arrhythmia, should be treated with antiarrhythmic drugs, as long as they can be effective. Side effects of these drugs, as good benefit often provided by a simple bradycardic treatment led to discuss it some 10 years ago 2 therapeutic strategies: rhythm control or rate control. But this choice widely highlighted in the previous guidelines, now seems simplistic. In 2010 we can probably offer two therapeutic goals, treat symptoms and treat cardiovascular risk associated with atrial fibrillation. The discomfort caused by symptomatic arrhythmia should always be assessed in our patients, as by the recent EHRA classification. Meanwhile fibrillation is part of the cardiovascular continuum, and is a marker of an additional risk: it appears certain that the control of this additional risk does not depend solely on the treatment of the arrhythmia itself

Total knee arthroplasty for osteoarthritis secondary to extra-articular malunions

SummaryIntroductionPost-traumatic total knee arthroplasty for extra-articular malunion requires correction of the deformity, either through asymmetrical bone resection (possibly inducing ligaments imbalance) or osteotomy at the time of arthroplasty. We report the results of a continuous multicenter, retrospective series of 78 patients (18 implants with osteotomy) with a mean 4 years of follow-up. The hypothesis is that the selected procedure requires to be based on the deformity's location and severity.PatientsWith a mean age of 63 years (younger in the osteotomy group), 38 patients had femoral malunion, 36 had tibial malunion, and four had a combined malunion. There were 70 frontal deformities (48 varus and 22 valgus) and 10 rotational deformities, often diaphyseal, four of which more than 20°. Twelve patients had a history of infection; eight had frontal laxity greater than 10°, and 15 a limited range of motion in flexion. In 70 cases, semi- or nonconstrained implants were used, and in eight cases more constrained implants, including four hinge prostheses.ResultsWe observed two deep infections, one case of avulsion of the extensor mechanism, and two cases of aseptic loosening with femoral malunion and varus deformity. Two osteotomies resulted in nonunion, one with internal fixation devices mobilization requiring revision using extension rods. The function and pain scores were significantly improved. The mobility improvements were moderate but did not compromise the surgical procedure main objective. The preoperative hip-knee angle was corrected with both techniques. Only the function score gain was greater for the isolated arthroplasty procedures.Discussion and conclusionThe indications for arthroplasty alone were extended to 20° varus and 15° valgus, with no major residual laxity. Beyond 10°, hinge prosthesis should be available. Associated osteotomy can correct rotational deformities that cannot be compensated with bone cuts. In deformities that are close to the joint, osteotomy facilitates implantation of moderately constrained prosthesis. This indication is based on CAT scan rotational deformities measurements because rotational deformities require an osteotomy, and/or the presence of extraligamentous deformity that cannot be reduced with collateral ligaments surgical release.Level of evidenceLevel 4. Non-controlled retrospective study

Les effets pro-arythmiques des médicaments

RésuméLes effets pro-arythmiques des médicaments sont fréquents et graves, et sont associés à une surmortalité non négligeable. La polymédication augmente le nombre d’effets indésirables et d’interactions graves voire mortelles. Certains sont facilement évitables. Cependant, au-delà de l’allongement de l’intervalle QT, d’autres mécanismes peuvent avoir un rôle majeur comme les dysfonctions du RyR2, responsable d’arythmie calcium-dépendantes par surcharge calcique intracellulaire, avec apparition de post-dépolarisations tardives, sans modifications de l’intervalle QT. Les bloqueurs des canaux sodiques sont également un problème sérieux de part le risque de démasquer ou d’aggraver une dysfonction du canal sodique chez des patients atteints de syndrome de Brugada asymptomatique ou non. Leur dépistage à un stade précoce du développement des médicaments peut avoir un intérêt majeur.SummaryThe cardiac safety of new and marketed drugs is a major concern for public authorities, patients, physicians as well as pharmaceutical companies. Letal adverse drug reactions are indeed a leading cause of death worldwide and increase at a greater rate than the increase in total hospital admission. The increasing use of polypharmacy in current clinical practice is also associated to a growing number of side effects and interactions leading to fatal adverse events. Measurement of the QT interval is an established, albeit incomplete, approach to assess the proarrhythmic risk of a drug. Ventricular arrhythmia (VA) can be caused by a QT-prolonging drug inducing abnormal repolarization of the action potential (AP) of ventricular cardiomyocytes. Emerging evidence, derived from recent understanding of these mechanisms and of similar mechanisms reported for heart failure (HF), suggest that diastolic Ca2+ leak from the sarcoplasmic reticulum (SR) related to RyR2 dysfunction can induce Ca2+ dependent arrhythmia. In this report, we review mechanisms underlying drug-induced arrhythmogenic effects and Ca2+ dependent arrhythmia, and, for the latter, we discuss some of the issues associated to worsening of cardiac arrhythmias

Water Absorption of Poly(methyl methacrylate) Measured by Vertical Interference Microscopy

PMMA (poly(methyl methacrylate)) is widely used to prepare orthopedic cements. They are in direct contact with cells and body fluids. PMMA, despite its hydrophobic nature, can absorb ?2% w/w water. We have evaluated by vertical interference microscopy if water absorption can produce a significant swelling in different types of PMMA blocks: pure, with a plasticizer, with a cross-linker, and in two types of commercial bone cements. Graphite rods which do not swell in water were used as internal standard. Hardness, indentation modulus, plastic, and elastic works were determined by nanoindentation under a 25mN fixed force. Vertical interference microscopy was used to image the polymer in the dry state and hydrated states (after 24 h in distilled water). On the surface of the polished polymers (before and after hydration), we measured roughness by the fractal dimension, the swelling in the vertical and the lateral directions. For each polymer block, four images were obtained and values were averaged. Comparison and standardization of the images in the dry and hydrated states were done with Matlab software. The average value measured on the graphite rod between the two images (dried and hydrated) was used for standardization of the images which were visualized in 3D. After grinding, a small retraction was noticeable between the surface of the rod and the polymers. A retraction ring was also visible around the graphite rod. After hydration, only the pure PMMA and bone cements had a significant swelling in the vertical direction. The presence of polymer beads in the cements limited the swelling in the lateral direction. Swelling parameters correlated with the nanoindentation data. PMMA can swell by absorbing a small amount of water and this induces a swelling that varies with the polymer composition and particle inclusions

Two-stage reconstruction of post-traumatic segmental tibia bone loss with nailing

Introduction Treatment of lower extremity segmental bone loss is difficult. Masquelet et al. proposed a two-stage technique: first, debridement and filling of bone loss with an acrylic spacer; second, bone reconstruction by filling with cancellous bone in the space left free (following cement removal) inside the so-called self-induced periosteal membrane. In the originally described technique, the fracture site is stabilized by an external fixator, which remains in place throughout the bone healing process, i.e., often longer than 9 months with all the known disadvantages of this type of assembly. Following the principle of two-stage reconstruction, we modified the technique by reconstructing around an intramedullary-locking nail placed in the first stage. Hypothesis This technique prevents the mechanical complications related to external fixator use and provides faster resumption of weight-bearing. Patients and methods Twelve patients were operated for segmental tibial bone loss greater than 6 cm resulting from injury (four cases) or aseptic necrosis (one case) or septic necrosis (seven cases). All the patients were operated on in an emergency setting and the first stage was performed before the 2nd week. A free muscle flap (ten patients) or a pediculated fasciocutaneous flap (two patients) was necessary during this first step to cover the site and provide good conditions for secondary bone growth. The follow-up was 39.5 months (range, 12–94 months). Results Complete weight-bearing was resumed at a mean 4 months. After the second step, all the patients except one had apparently healed (complete weight-bearing with no pain). Five septic complications occurred after the second step, in one case leading to reconstruction failure. Four other patients had infectious complications successfully treated (as of the last follow-up) either by changing the nail in two cases or by prolonged antibiotic therapy in two other cases, with no graft loss. Discussion The use of the intramedullary nail facilitates the Masquelet technique by allowing the patient to resume weight-bearing more quickly and avoiding secondary fractures. However, the risk of sepsis remains high but can be controlled without compromising the final bone union in four cases out of five. Level of evidence Level IV. Retrospective study