Distribution by Scientific Domains
Distribution within Physics and Astronomy

Kinds of Dislocations

  • edge dislocation
  • hip dislocation
  • interfacial dislocation
  • joint dislocation
  • misfit dislocation
  • threading dislocation

  • Terms modified by Dislocations

  • dislocation core
  • dislocation creep
  • dislocation density
  • dislocation loop
  • dislocation network
  • dislocation structure

  • Selected Abstracts

    About 200 years after Mohs , Nanoscratching LiB3O5

    P. Paufler
    Abstract Though simple scratch hardness tests after Mohs are still used today, the development of diamond nanoscratching equipment offers new possibilities to meet demands of modern nanotechnology. Preceding approaches to assign hardness values to materials are briefly reviewed, and scratch hardness is related to indentation hardness. Taking single-crystalline LiB3O5 as an example, the dependence of scratch morphology on the direction of scratching is demonstrated quantitatively. The coefficient of friction depends on normal load and varies between 0.25 and 0.37. Moreover, it is oscillating during scratching thus reflecting processes at nanoscale. Dislocation etch pits were observed due to scratching. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Dislocation of an upper third molar into the maxillary sinus after a severe trauma: a case report

    Heng-Xing Cai
    Abstract , Dental injuries are common following facial trauma. This article presents a rare injury: the dislocation of a third molar into the maxillary sinus after complex mandibular and maxillary tuberosity fractures. The possible mechanism and clinical treatment are discussed. [source]

    Human Vulnerability, Dislocation and Resettlement: Adaptation Processes of River-bank Erosion-induced Displacees in Bangladesh

    DISASTERS, Issue 1 2004
    David Mutton
    The purpose of this research was to identify and analyse patterns of economic and social adaptation among river-bank erosion-induced displacees in Bangladesh. It was hypothesised that the role of social demographic and socio-economic variables in determining the coping ability and recovery of the river-bank erosion-induced displacees is quite significant. The findings of the research reveal that displacees experience substantial socio-economic impoverishment and marginalisation as a consequence of involuntary migration. This in part is a socially constructed process, reflecting inequitable access to land and other resources. Vulnerability to disasters is further heightened by a number of identifiable social and demographic factors including gender, education and age, although extreme poverty and marginalisation create complexity to isolate the relative influence of these variables. The need to integrate hazard analysis and mitigation with the broader economic and social context is discussed. It is argued that the capacity of people to respond to environmental threats is a function of not only the physical forces which affect them, but also of underlying economic and social relationships which increase human vulnerability to risk. Hazard analysis and mitigation can be more effective when it takes into account such social and demographic and socio-economic dimensions of disasters. [source]

    Palaeopathological and palaeogenetic study of 13 cases of developmental dysplasia of the hip with dislocation in a historical population from southern France

    B. Mafart
    Abstract Dislocation of the hip can be consecutive to developmental dysplasia of the hip that is linked to a complex set of genetic and mechanical factors. The purpose of this report is to describe 13 cases of complete dysplastic hip dislocation observed in the skeletal remains of nine women exhumed from an historical gravesite dating from the 5th to 17th centuries in southern France. Despite the size of this palaeopathological series, which is the largest study published to date, findings indicate that the prevalence of hip dislocation in this historical sample was still lower than in some French areas at the beginning of the 20th century. Mitochondrial DNA sequencing demonstrated possible kinship only between two women, i.e. one who died in the period from the 11th to 13th centuries and another who died in the period from the 16th to 17th centuries. It is suggested that the tight swaddling of young infants in France up to the end of the 19th century could have been a predisposing factor for this highly debilitating disorder. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    The Geography of Meanings: Psychoanalytic Perspectives on Place, Space, Land and Dislocation edited by Hooke, Maria Teresa Savio & Akhtar, Salman

    James Astor
    No abstract is available for this article. [source]

    Retropharyngeal Pseudomeningocele Presenting as Dysphagia After Atlantooccipital Dislocation,

    THE LARYNGOSCOPE, Issue 9 2006
    Dr. David M. Cognetti MD
    Abstract Educational Objective: At the conclusion of this paper, the readers should be able to recognize a retropharyngeal pseudomeningocele as a potential complication of atlanto occipital dislocation. Objectives: To demonstrate how a retropharyngeal pseudomeningocele may present as dysphagia in a patient who is recovering from atlanto occipital dislocation as well as to discuss the treatment options in this situation. Study Design: Case report and literature review. Methods: Analysis of a case through medical record and literature review. Results: A retropharyngeal pseudomeningocele is a very rare complication of atlanto occipital dislocation. It may develop weeks after the initial injury and can present with respiratory or swallowing difficulties. Decompression via a ventriculoperitoneal or lumboperitoneal shunt facilitates resolution of the cerebral spinal fluid collection. Conclusions: A retropharyngeal pseudomeningocele should be considered in all patients status post-atlanto occipital dislocation who are experiencing respiratory distress or dysphagia. [source]

    Learning and Knowledge in an Office Workplace: Perceptions of the Recently Unemployed

    Paul G. Letkemann
    Abstract This paper uses interview data from employees and former employees of a Regional Land Use Planning Commission Office in Alberta, Canada. This workplace is unified by a sense of common social and environmental purpose revolving around the Regional Planning Act of Alberta. Occupationally specific contextual parameters allow collective recognition of roles symbolizing knowledge acquisition, contributing to self-validation in the workplace. By emphasizing perceptions of recently unemployed people, this paper incorporates what Marcus called 'processes of reconceptualization' in understandings of the importance of workplace achievement and position. Dislocation from workplace position is also removal from ongoing processes of learning, teaching, applied knowledge and social contribution. In rethinking their loss, the recently unemployed express often-overlooked interpretations of knowledge based workplace dynamics. [source]

    Anterior Shoulder Dislocation: The Scapular Manipulation Technique

    Brandon C. Tudor MD
    No abstract is available for this article. [source]

    Dynamics of Dislocations in a 2D Plasma Crystal

    V. Nosenko
    Abstract Recent experimental results on the dislocation dynamics in a two-dimensional plasma crystal are reviewed. A single layer of micron-size microspheres was suspended in the sheath of a capacitively coupled rf discharge. The particles self-organized in a triangular lattice. Edge dislocations were created in pairs in this plasma crystal when the internal shear stress built up above a threshold, due to the crystal's slow differential rotation. Basic stages of dislocation nucleation were identified and studied, from gradual pile-up of shear strain in the crystal to eventual escape of free dislocations. After nucleation, dislocations moved supersonically with respect to the shear waves and generated shear-wave Mach cones (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Dislocations as Active Components in Novel Silicon Devices,

    Martin Kittler
    Abstract The electrical and optical properties of dislocations in Si are reviewed, namely dislocation-related recombination and luminescence, transport of minority and majority carriers along dislocations or the electric field around dislocations. It is shown that Si wafer direct bonding allows well-controlled formation of dislocation networks, giving rise to adjustable dislocation properties. Ideas for novel Si devices utilizing dislocations as active components are presented. In particular, dislocation-based light emitters at about 1.5,µm wavelength are demonstrated. Concepts for dislocation-based conductive channels and fast FETs, manipulators of biomolecules or thermo-electric generators are sketched. [source]

    The Spatial Distribution of Threading Dislocations in Gallium Nitride Films

    ADVANCED MATERIALS, Issue 38-39 2009
    Michelle A. Moram
    Spatial analysis techniques are used to study threading dislocations (TDs) at the surfaces of a wide range of GaN films. In all films, the dislocation positions are consistent with a spatially random TD generation process followed by movement of dislocations, but are inconsistent with the spatial distribution of dislocations expected at island coalescence boundaries. [source]

    First combined electron backscatter diffraction and transmission electron microscopy study of grain boundary structure of deformed quartzite

    Summary The structures of boundaries in a deformed and dynamically recovered and recrystallized quartz polycrystal (mylonite) were characterized by transmission electron microscopy, after the misorientation angles across the same grain boundaries had been analysed using electron backscatter diffraction in a scanning electron microscope. In this new approach, a specific sample area is mapped with electron backscatter diffraction, and the mapped area is then attached to a foil, and by the ion beam thinned for transmission electron microscopy analysis. Dislocations in grain boundaries were recognized as periodic and parallel fringes. The fringes associated with dislocations are observed in boundaries with misorientations less than 9°, whereas such fringes cannot be seen in the boundaries with misorientations larger than 17°. Some boundaries with misorientations between 9° and 17° generally have no structures associated with dislocation. One segment of a boundary with a misorientation of 13.5° has structures associated with dislocations. It is likely that the transition from low-angle to high-angle boundaries occurs at misorientations ranging from approximately 9° to 14°. Change in the grain boundary structure presumably influences the mobility of the boundaries. In the studied deformed quartz vein, a relative dearth of boundaries between misorientation angles of , = 2° and , = 15° has previously been reported, and high-angle boundaries form cusps where they intersect low-angle boundaries, suggesting substantial mobility of high-angle boundaries. [source]

    Dissociation of the ,001, Dislocations and Their Interactions with Dislocation Loops in Tetragonal BaTiO3

    Shun-Yu Cheng
    Dislocations in pressureless-sintered BaTiO3 ceramics have been analyzed using transmission electron microscopy. Subjected to effective sintering stresses, dislocations were generated and multiplied in plastically deformed BaTiO3 crystals by the Frank,Read mechanism from both single- and double-ended sources. This is represented by dislocations encompassing a series of square-like borders that shared a common center. All border dislocations exhibited the characteristic scallop shape. True dislocation line directions (u) were determined by trace analysis and Burgers vectors (b) by contrast analysis for the dislocations dissociated from b=,001, into two half-partials following the type (I) reaction ofby climb on {001}. Dislocation interactions between the main dislocations created from plastic deformation and dislocation loops of b=,100, or ,110, forming condensation of intrinsic Schottky vacancies were also found to obey the type (IV) reaction of, the type (V) reactions of. Migrating dislocations and loops interacting mutually in several stages, illustrated schematically, before arriving at the configuration described by types (IV) and (V) were observed and discussed. [source]

    Gliding dislocations in Bi2Te3 materials

    N. Peranio
    Abstract In Bi2Te3, dislocations were found with an uniquely high mobility at room temperature. The gliding dislocations were analysed and their effect on the thermoelectric properties is discussed. The glide of dislocations was induced by heating with a focused electron beam at 120 keV, external stresses were not applied. The dislocations were bowed out in the glide direction and were only pinned at the surface of the samples. Stereomicroscopy combined with image simulations yielded basal plane dislocations with a density of 109 cm,2 and Burgers vectors of type ,110,. Video sequences showing the glide of single dislocations and groups of dislocations were recorded. Isolated dislocations showed a high mobility in ±,110, direction at a velocity of 10,100 nm s,1. Dislocation dipoles were pinned and did not glide. Dislocations equidistantly arranged within the same glide plane showed a collective movement. Dislocations piled up in different glide planes were fixed and acted as barriers for gliding dislocations. The motion of dislocations was attributed to residual shear stresses of about 10 MPa, and their glide directions depended on the sign of the Burgers vector. Attractive and repulsive forces of dislocations directly visualise the forces due to the elastic strain fields of other dislocations. The relevance of phonon scattering on dislocations in Bi2Te3, particularly due to their high mobility and density, was confirmed by two inspections: (i) Dislocations decrease the lattice thermal conductivity due to phonon scattering on the elastic strain field. The phonon mean free path was estimated to about 800 µm at 3 K and agreed with published data. (ii) The dislocation resonance theory of Granato and Lücke predicts an interaction between phonons and dislocations acting as oscillating strings. The attenuation of ultrasound was estimated and was compared with published data. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Etch-pits and threading dislocations in thick LEO GaN films on sapphire grown by MOCVD

    Lu Min
    Abstract High quality Lateral Epitaxial Overgrowth (LEO) GaN films on (0001) sapphire substrates were grown by a commercial MOCVD system (Thomas Swan Corp.). We have studied the etch-pits and threading dislocations in GaN films by wet etching of pits, HCl vapor etching of pits and Scanning Electron Microscope (SEM). SEM images of GaN films etched in HCl vapor and molten KOH gave us notably different etching pits densities in the different region of LEO GaN films, which confirmed HCl vapor etching could show three kinds of Threading Dislocations (TDs), while molten KOH wet etching only could show pure screw TDs. In region above window TDs density is high (about 3 × 108/cm2) and edge TDs are in the majority, while it is almost free of TDs in region above mask, and only in middle region above mask there are some TDs (including all three kinds) and also edge TDs are in the majority. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Thick crack-free AlGaN films deposited by facet-controlled epitaxial lateral overgrowth

    R. Liu
    Abstract Thick crack-free AlGaN films have been grown on inclined-facet GaN templates. Light emitting diodes with , = 323 nm has been achieved on these epilayers. The GaN template was grown at a low temperature in order to obtain triangle-facet growth fronts. Subsequent growth of AlGaN on this template involving a lateral overgrowth process exhibits interesting properties. The microstructure and optical characterizations were done using transmission electron microscopy and cathodoluminescence. At the AlGaN/GaN interface, a high density of dislocations was created due to lattice mismatch strain. Another unexpected set of triangular boundaries was observed inside the AlGaN layer, which grew without any change of the growth parameters. These boundaries were found to arise from domains grown in different directions. Mono-chromatic cathodoluminescence images indicate that Al content is different between the vertically-grown and the laterally-grown domains, suggesting that lattice mismatch strain exists between them. Dislocations were created at these mismatched boundaries to relax the strain. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Metalorganic Chemical Vapor Deposition Growth of a GaN Epilayer on an Annealed GaN Buffer Layer

    F. Degave
    Abstract We investigated the growth of an epitaxial layer deposited on an annealed buffer layer using transmission electron microscopy. It is shown that crystalline quality of the epitaxial layer depends on the annealing conditions of the buffer layer. Dislocations and formation of V-shaped defects are observed and may originate from the structure and morphology of the buffer layer. [source]

    Interaction between a dislocation and monovalent anion in various alkali halide crystals

    Y. KohzukiArticle first published online: 30 AUG 2010
    Abstract It was investigated from (L0/L)2 versus ,0 curve that the Friedel relation between the effective stress and the average length of dislocation segments, L, is appropriate for the interaction between a dislocation and the monovalent anion in various alkali halides single crystals (NaCl: Br - , NaBr: Cl - or I - , KCl: Br - or I - , and RbCl: Br - or I - ). Here, L0 represents the average spacing of monovalent anions on a slip plane and ,0 is the bending angle at which the dislocation breaks away from the anion at the temperature of 0 K. This is because the anions are the weak obstacles such as impede the dislocation at ,0 above about 150 degrees, where the Friedel relation agrees with the Fleischer one (L02 = L2(,,,0)/2). Furthermore, the values of (L /L0) were found to be within 4.05 to 5.87 for the crystals. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Interdiffusion phenomena in InGaAs/GaAs superlattice structures

    B. Sar, kavak
    Abstract We have studied structural properties of InGaAs/GaAs superlattice sample prepared by Molecular Beam Epitaxy (MBE) using high resolution X-ray diffractometer (HRXRD). Increasing strain relaxation and defect generations are observed with the increasing Rapid Thermal Annealing (RTA) temperature up to 775 °C. The higher temperatures bring out relaxation mechanisms; interdiffusion and favored migration. The defect structure and the defects which are observed with the increasing annealing temperature were analyzed. Firstly, the in-plane and out-of-plane strains after the annealing of sample were found. Secondly, the structural defect properties such as the parallel X-ray strain, perpendicular X-ray strain, misfit, degree of relaxation, x composition, tilt angles and dislocation that are obtained from X-ray diffraction (XRD) analysis were carried out at every temperature. As a result, we observed that the asymmetric peaks especially in asymmetric (224) plane was affected more than symmetric and asymmetric planes with lower polar or inclination angles due to c-direction at low temperature. These structural properties exhibit different unfavorable behaviors for every reflection direction at the increasing temperatures. The reason is the relaxation which is caused by spatially inhomogeneous strain distribution with the increasing annealing temperature. In the InGaAs superlattice samples, this process enhances preferential migration of In atoms along the growth direction. Further increase in the annealing temperature leads to the deterioration of the abrupt interfaces in the superlattice and degradation in its structural properties. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Characterization of dislocation structures in copper single crystals using electron channelling contrast technique in SEM

    Xiao-Wu Li
    Abstract The dislocation structures induced by low-plastic-strain-amplitude cyclic deformation of [111] multiple-slip-oriented Cu single crystals were investigated using electron channelling contrast (ECC) technique in scanning electron microscopy (SEM). At a low plastic strain amplitude ,pl of 8.8 × 10,5, the saturated dislocation structure is mainly composed of labyrinth-like vein structure (or irregular labyrinths), and the cyclic hardening behavior at such a low ,pl is interpreted as being the result of dislocation multiplication by a Frank-Read mechanism. As ,pl increases to 4.0 × 10,4, the unsaturated dislocation structure exhibits two kinds of distinctive configurations, i.e., dislocation walls and misoriented cells. Interestingly, these misoriented dislocation cells are strictly aligned along the primary slip plane (111), constituting a unique persistent slip band (PSB) structure. Here, these cells are thus called PSB cells. In addition, there is a locally distinctive region comprising some cells having a recrystallization-like feature in the whole structure of PSB cells. The formation of the structure of PSB cells is discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Dislocation cell structures in melt-grown semiconductor compound crystals

    P. Rudolph
    Abstract The phenomenon of dislocation patterning during melt growth of III-V, II-VI and IV-VI semiconductor crystals is discussed. The paper is focused on the formation of cellular structures driven by the growth inherent thermo-mechanical stress. Of particular interest is the scaling of relations between cells size, dislocation density and acting shear stress. Among the materials there are characteristic similarities but also significant variations of the cell genesis. After the related compound specifics are discussed possible measures for retardation of cell patterning during growth are demonstrated. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Dental injuries resulting from tracheal intubation , a retrospective study

    Jobst Vogel
    Thus, this retrospective study was conducted including the data of 115,151 patients. All patients involved had been exposed to general anesthesia between 1995 and 2005. The resulting tooth injuries were assessed according to the following parameters: age, kind of hospital conducting treatment, intubation difficulties, pre-existing tooth damage, type and localization of tooth, type of tooth damage, and the number of teeth injured. At least 170 teeth were injured in 130 patients, while patients 50 years of age and older were especially affected. In contrast to older patients where in the majority of cases the periodontium (lateral dislocation) was injured, in younger patients dental hard tissue (crown fracture) was more likely to be affected. It was calculated that patients from the cardiothoracic surgery clinic were showing the highest risk of tooth damage. In more than three-fourth of all cases the anterior teeth of the maxilla, especially the maxillary central incisors, were affected. Pre-existing dental pathology like caries, marginal periodontitis and tooth restorations were often distinguishable prior to operation. Mouthguards in connection with tracheal intubation are not generally recommended as preventive device, due to the already limited amount of space available. Instead, pre-existing risk factors should be thoroughly explored before the induction of intubation narcosis. [source]

    Recurrent trauma histories of two ,unlucky teeth': 42-month follow-up

    Zuhal K
    The fracture type, severity of dislocation, mobility of fragments and diastasis have negative influence on the healing process. The aim of this study was to describe the treatment and the 42-month follow-up period of three trauma histories in a 12-year-old patient in 1 year and to emphasize the negative effects of recurrent traumas on the healing pattern and prognosis of root fractures. [source]

    Effect of crown fracture on the surrounding periodontium

    Janaína Cristina Gomes
    To reach the long axis of the tooth, an impact device was applied to eight teeth of four adult dogs to produce trauma. Crown fractures involving the enamel and dentin, with or without pulpar exposure and without dislocation, mobility or gingival bleeding were analyzed within the post-trauma periods of 30 min, 1, 3, and 7 days. The force of impact that resulted in coronary fracture, although dissipated at the time of fracture, reverberated in the surrounding periodontium and may generate not only light histological alterations with a rapid re-establishment of the tissues, but also an intense inflammatory condition required as long as 7 days to clear up. The gravity of these inflammatory reactions unleashed in these teeth's periapical tissues depends on the absorption of impact by the periodontal structures and the individual susceptibility of each organism. [source]

    Clinical and histological alterations in the surrounding periodontium of dog's teeth submitted for an intrusive luxation

    Janaína Cristina Gomes
    An impact device was used on 12 teeth of six adult dogs with the purpose of making a dislocation on the long axis of these teeth. Of the teeth that suffer intrusion luxation, two did not receive treatment and ten were replaced by orthodontic extrusion with activated springs of 100 gf. The traction was initiated either immediately after the trauma or 7 days later. Observation time was 40 days. Endodontic therapy with calcium hydroxide was performed on the fourteenth day after the intrusive luxation. The intruded teeth that did not receive appropriate treatment had signs of extensive and progressive inflammatory resorption. The teeth that were moved immediately after the trauma had lesser degree of replacement resorption compared with those that were extruded 7 days after the trauma. [source]

    Dislocation of an upper third molar into the maxillary sinus after a severe trauma: a case report

    Heng-Xing Cai
    Abstract , Dental injuries are common following facial trauma. This article presents a rare injury: the dislocation of a third molar into the maxillary sinus after complex mandibular and maxillary tuberosity fractures. The possible mechanism and clinical treatment are discussed. [source]

    Healing and prognosis of teeth with intra-alveolar fractures involving the cervical part of the root

    Miomir Cvek
    Abstract Healing and long-term prognosis of 94 cervical root fractures were evaluated. The teeth were divided into two groups according to type of fracture: transverse fractures limited to the cervical third of the root (51 incisors) and oblique fractures involving both the cervical and middle parts of the root (43 incisors). Neither the frequency nor the type of fracture healing differed significantly between the two groups. In the material as a whole, healing of the fracture with hard tissue formation was observed in 17 teeth (18%), and healing with interposition of periodontal ligament (PDL) and, in some cases, hard tissue between the fragments in 62 teeth (66%). Fifteen teeth (16%) showed no healing and a radiolucency adjacent to the fracture. Statistical analyses revealed that incomplete root formation and a positive sensibility test at the time of injury were significantly related to both healing and hard tissue repair. The same applied to concussion or subluxation compared with dislocation of coronal fragment, as well as optimal compared with suboptimal reposition of displaced coronal fragments. The type and duration of splinting (or no splinting) appeared to be of no significance for frequency or type of healing of cervical root fractures. During the observation time (mean = 75 months), 19 (44%) of the teeth with transverse fractures and 3 (8%) of those with oblique fractures were lost after healing. In conclusion, fractures in the cervical part of the root had a healing potential and the predictive parameters identified for fractures in other parts of the root seemed to be valid for the healing of cervical root fractures. Transverse fractures appeared to have a significantly poorer long-term prognosis compared to oblique fractures, apparently due to a marked post-treatment mobility, which often led to new luxation caused by even minor impacts. [source]

    Proximal femoral resection for subluxation or dislocation of the hip in spastic quadriplegia

    Steve Ackerly MD
    Management of a painful or contracted hip dislocation in individuals with severe spastic quadriplegia is difficult. Clinical and radiographic results of 12 proximal femoral resection-interposition operations performed in seven non-ambulatory persons (five males, two females; mean age 14 years, 8 months; age range 6 years 11 months to 19 years 8 months) with severe spasticity were reviewed to determine if pain relief and restoration of motion were maintained. At a mean follow-up of 7 years 7 months (median 9 years 6 months) all participants maintained a good sitting position and a functional range of motion with improved hygiene. Hip pain was improved in all participants compared with their preoperative status. Proximal femur migration occurred causing slight pain in one person. Heterotopic ossification was observed but was not clinically significant. Complications included traction pin loosening and infection and a late supracondylar femur fracture 3 months after the operation. Proximal femoral resection effectively decreased pain and restored hip motion in those with severe spastic quadriplegia leading to improved sitting and perineal care. [source]

    Antireflux stents for palliation of malignant esophagocardial stenosis

    K. Schoppmeyer
    SUMMARY., Placement of self-expanding metal stents (SEMS) for palliation of malignant stenoses at the gastroesophageal junction is often associated with stent migration and reflux symptoms. SEMS with an antireflux mechanism have been developed to overcome the latter problem. The aim of this study was to evaluate the safety and efficacy of antireflux Z-stents. Patients with advanced squamous cell or adenocarcinoma of the distal esophagus or cardia suffering from dysphagia received an antireflux Z-stent. Technical success, complications of the procedure, clinical symptoms before and after stent placement, reinterventions and survival were recorded. Follow-up was accomplished by patient interviews and a standardized questionnaire for primary care physicians. Eighteen consecutive patients received an antireflux Z-stent. Seventeen of 18 stents were placed technically successful in a single endoscopic procedure. Mean dysphagia score improved from 2.2 to 0.6. Four patients (22%) had permanent reflux symptoms, an additional nine (50%) were taking proton pump inhibitors on a regular basis. In 10 patients, a re-intervention was necessary mainly due to dislocation of the stent. To ensure adequate nutrition three and two patients received a percutaneous gastrostomy and a jejunostomy, respectively. Median survival from stent insertion was 54 days (range, 3,201). Although placement of an antireflux Z-stent is technically feasible, its application is hampered by frequent stent migration and insufficient prevention of gastroesophageal reflux. Further technical improvements of stents or alternative methods like brachytherapy are required for satisfactory palliation of malignant gastroesophageal stenosis. [source]

    Surviving atlanto-occipital dislocation

    Benjamin M Bloom
    Abstract Traumatic atlanto-occipital dislocation carries a significant mortality and morbidity. We present the clinical and radiological features of a case of traumatic skeletal and central nervous system disunion. Thanks to a combination of early resuscitation and luck, the patient survived an improbably severe injury to leave hospital and enjoy a degree of independent life. Such severe injuries are usually fatal and the literature on such extensive cervical disruption is often confined to postmortem evidence. [source]