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Debye screening of dislocations.

Debye-like screening by edge dislocations of some externally given stress is studied by means of a variational approach to coarse grained field theory. Explicitly given are the force field and the induced geometrically necessary dislocation (GND) distribution, in the special case of a single glide axis in 2D, for (i) a single edge dislocation and (ii) a dislocation wall. Numerical simulation demonstrates that the correlation in relaxed dislocation configurations is in good agreement with the induced GND in case (i). Furthermore, the result (ii) well predicts the experimentally observed decay length for the GND developing close to grain boundaries.

Journal Article↗

Repetitive intraoperative dislocation during transvenous left ventricular lead implantation: usefulness of the retained guidewire technique.

Dislocation of the transvenous left ventricular lead has been reported in a substantial number of patients selected for cardiac resynchronization therapy. We describe a novel technique using a retained guidewire in patients with repetitive intraoperative dislocation to stabilize the lead in its final position. Pacing and sensing parameters between patients in whom the retained guidewire technique was used (n = 6) were not significantly different as compared to the group of patients (n = 67) without this technique during a 6-month follow-up. No dislocations were observed in the group of patients with the retained guidewire technique and fluoroscopic evaluation did not reveal (minor) dislocation. This technique might be considered for patients with repetitive intraoperative left ventricular lead dislocation.

Electrodes, Implanted↗

Dislocations in complex materials.

Deformation of metals and alloys by dislocations gliding between well-separated slip planes is a well-understood process, but most crystal structures do not possess such simple geometric arrangements. Examples are the Laves phases, the most common class of intermetallic compounds and exist with ordered cubic, hexagonal, and rhombohedral structures. These compounds are usually brittle at low temperatures, and transformation from one structure to another is slow. On the basis of geometric and energetic considerations, a dislocation-based mechanism consisting of two shears in different directions on adjacent atomic planes has been used to explain both deformation and phase transformations in this class of materials. We report direct observations made by Z-contrast atomic resolution microscopy of stacking faults and dislocation cores in the Laves phase Cr2Hf. These results show that this complex dislocation scheme does indeed operate in this material. Knowledge gained of the dislocation core structure will enable improved understanding of deformation mechanisms and phase transformation kinetics in this and other complex structures.

Journal Article↗

Imperfect oriented attachment: dislocation generation in defect-free nanocrystals

Dislocations are common defects in solids, yet all crystals begin as dislocation-free nuclei. The mechanisms by which dislocations form during early growth are poorly understood. When nanocrystalline materials grow by oriented attachment at crystallographically specific surfaces and there is a small misorientation at the interface, dislocations result. Spiral growth at two or more closely spaced screw dislocations provides a mechanism for generating complex polytypic and polymorphic structures. These results are of fundamental importance to understanding crystal growth.

Journal Article↗

Dislocations faster than the speed of sound

It is thought that dislocations cannot surpass the sound barrier at the shear wave velocity because the energy spent in radiation has a singularity there. Atomistic simulations show that dislocations can move faster than the speed of sound if they are created as supersonic dislocations at a strong stress concentration and are subjected to high shear stresses. This behavior is important for the understanding of low-temperature deformation processes such as mechanical twinning and may be relevant for the dynamics of tectonic faults. The motion of the dislocations at a speed of 2 times the shear wave velocity can be understood from a linear elastic analysis, but many of the peculiarities of the supersonic dislocations are dominated by nonlinear effects that require a realistic atomistic description.

Journal Article↗

Posterior dislocation of an intraocular lens implant and its removal.

The cause of dislocation of an intraocular lens is a direct blow or jerk, and dislocation may complicate both iris-supported and capsule-supported lenses. In capsule-supported lenses the implant dislocates towards the anterior chamber but in iris-supported lenses the dislocation is posterior. A technique for removal of a posterity dislocated lens is described.

Cataract Extraction↗

Role of dislocation loops on the elastic constants of lyotropic lamellar phases.

We study the role of dislocation loops defects on the elasticity of lamellar phases by investigating the variation of the lamellar elastic constants, B and K, induced by the proliferation of these defects. We focus our interest on one particular lamellar phase made up of a mixture of C(12)E(5) and DMPC in water, which is already well-characterised. This lamellar phase undergoes a second-order (or weakly first-order) lamellar-to-nematic phase transition at about 19 degrees C and dislocation loops are seen to proliferate within the lamellar structure when temperature is decreased below 30 degrees C. The values of both elastic constants of this given lamellar phase are measured as a function of temperature, approaching the lamellar-to-nematic transition, with the help of Quasi-Elastic Light Scattering (QELS) on oriented lamellar phases. Very surprisingly we observe a strong and rapid increase in both Band K as the lamellar-to-nematic transition temperature is approached. These increases are seen to start as soon as dislocation loops can be observed in the lamellar phase. We interpret our results as being the consequence of the appearance and proliferation of dislocation loops within the lamellar structure. According to a simple model we developed we show that B and K are proportional to the density of dislocation loops in the lamellar phase.

Colloids↗

Crystallite-size distribution and dislocation structure in nanocrystalline HfNi5 determined by x-ray diffraction profile analysis.

A rapidly quenched nanocrystalline Hf11Ni89 alloy was produced by melt-spinning. The x-ray phase analysis shows that the as-quenched ribbon consists mainly of nanocrystalline fcc HfNi5 although a small amount of Ni(Hf) solid solution is also detected. The crystallite size distribution and the dislocation structure of the dominant HfNi5 phase were determined by a recently developed method of diffraction profile analysis. In this procedure, by assuming spherical shape and log-normal size distribution of crystallites, the Fourier coefficients of the measured physical profiles are fitted by the Fourier coefficients of well established ab initio functions of size and strain peak profiles. The anisotropic broadening of peak profiles is accounted for by the dislocation model of the mean square strain in terms of average dislocation contrast factors. It was found that the median and the variance of the crystallite size distribution are 3.3 nm and 0.82, respectively. The dislocation density is 3.7 x 10(16) m-2 and the character of dislocations is nearly pure screw. The results obtained from x-rays were in good agreement with transmission electron microscopy observations.

Alloys↗

A dislocation of the inner head in bipolar prosthesis with a self-centering system: a case report.

We present a case of inner head dislocation 11 years after the replacement of a bipolar prosthesis with a self-centering system. An 84-year-old woman with osteoarthritis of the left hip underwent a replacement of the Bateman UPF-II bipolar prosthesis in 1987. She fell off a chair on April 19 1998, and felt a sudden sharp pain in the left hip. Roentgenograms revealed that the inner head was dislocated from the outer head. Moreover, on June 19, when she stood up from the floor, the dislocation recurred. On July 23, a revision surgery was carried out. When the outer head was removed from the acetabulum, the bearing insert was markedly worn by the impingement of the femoral stem neck. Because there was no evidence of loosening of the femoral stem, a cemented replacement of the acetabular component was performed. At a 2-year follow-up, she had mild hip pain, but had returned fully to daily living. Our review of current published studies reveals that most inner head dislocations occurred in osteoarthritic patients. Thus, the occurrence of dislocations may be more dependent on patient selection than on failure of the bipolar prosthesis itself.

Aged↗

[Osteosynthesis with Kirschner pin fixation in treatment of fractures with dislocation of the lateral condyle of the humerus in a pediatric population].

INTRODUCTION: Fractures of lateral condyle represent 17% of all pediatric fractures of the distal humerus, and in current pediatric orthopedics there is still no agreement regarding optimal treatment modalities. We presented a treatment protocol for pediatric dislocated fractures of the lateral condyle of the humerus used at the Pediatric Surgery Clinic in Novi Sad. MATERIAL AND METHODS: Over the study period (1991-2000) a total of 48 patients with dislocated fractures of the lateral condyle of the humerus were hospitalized at the Pediatric Surgery Clinic. Orthopedic reduction and percutaneous pin fixation under radiological supervision was done in 15 patients, while 33 patients needed surgical reduction and pin fixation. RESULTS: Satisfactory results were obtained in 42 patients (91.3%), out of which 29 patients (63.1%) presented with excellent results. Good results were obtained in 8 patients (17.4%), and fair results in 5 patients (10.8%). Unsatisfactory results were present in 4 patients (8.7%). Two patients were lost to follow-up. DISCUSSION: Dislocation fractures of the lateral condyle represent high risk for development of complications. Adequate diagnosis and treatment represent basic conditions for successful postinterventional result. Orthopedic reduction with percutaneous pin fixation is recommended for fractures that may be anatomically reduced. In cases of unsatisfactory results of reduction, as well as in cases with completely dislocated and rotated fragments, surgical reduction and pin fixation is necessary. CONCLUSIONS: Satisfactory results in 91.3% of cases, and long-term experience suggest that the recommended therapeutic option is adequate in treatment of dislocated fractures of the lateral condyle of the humerus in pediatric population.

Adolescent↗

Subaxial antero-posterior dislocation of the cervical spine in rheumatoid arthritis.

A subaxial (below C2) antero-posterior dislocation of the cervical spine was present in 18% of 407 patients with rheumatoid arthritis. The dislocation was as common at only one level as at two more levels and was more severe if the height of the spinous process was reduced. Most of these same patients also had an atlanto-axial dislocation. At follow-up examinations, the frequency of a subaxial dislocation was the same in patients with a severe atlanto-axial dislocation who were receiving conservative treatment as in patients with a cervico-occipital fusion. Neurological symptoms occurred more frequently in patients with an encroached spinal canal and in patients with a reduced height of the entire cervical spine.

Adult↗

Hindfoot Dislocations: When Are They Not Benign?

Acute hindfoot dislocations are usually characterized by displacement of both the talocalcaneal and the talonavicular joints. Medial dislocations are more common than lateral ones. Closed reduction is usually obtained easily. When closed attempts fail, surgical exploration and removal of recognized obstacles to reduction are necessary. Associated open wounds necessitate aggressive operative management to prevent infection. Postreduction radiographs should be scrutinized for the presence of associated fractures that require fixation or surgical removal. A short-leg walking cast should be used for 3 to 6 weeks. In rare instances, the tibiotalar joint is also dislocated, which usually necessitates open reduction or, if the injury is open, extruded, and contaminated, talar excision. All hindfoot dislocations result in some stiffening of the hindfoot. Painful degenerative arthrosis sometimes develops after this injury. Factors that predispose to poor outcomes include high-energy mechanisms, the presence of open wounds and fractures, and lateral dislocations. Painful arthrosis that does not respond to conservative treatment can be treated with selective hindfoot arthrodesis.

Journal Article↗

[Chronic functional dislocation of the cervical spine with radiculo-spinal effects. Discectomy by anterior route and fusion without graft].

X ray dynamic study of cerevical spine movements in 12 patients with neurological impairment has shown an abnormal mobility between two vertebrae in the anterior or posterior direction. This abnormal mobility which has been called functional dislocation, is situated usually over major discarthrosic lesions rather than under. This dislocation, which appears during voluntary and automatic movements of the head and neck has been qualified chronic. A discectomie through an anterior surgical approach and a bony fusion of vertebral bodies without any graft at the dislocation site lead to 10 good results. 2 failures have been imputed to the fact that there was a 10 years evolution of a tetraplegia before operation. The pathogenesis of chronic functional dislocation of the cervical spine is discussed with regard to compression and stretching of the spinal cord, roots and arteries of both. Traumatism of vertebral arteries during dislocation remain under discussion.

Cervical Vertebrae↗

Simplified technique to remove posteriorly dislocated lens implants.

Visual loss caused by posterior dislocation of an intraocular lens (IOL) may be managed by placement of a secondary IOL without removal of the dislocated IOL. However, the improved visual acuity may lead to visual disturbances from the mobile, dislocated IOL. Removal of dislocated implants through the pars plana entails risks of a large pars plana incision to include hemorrhage, hypotony, and a greater potential for vitreous traction caused by extraction across the vitreous base. Removal via the corneal limbus lessens these risks but is made more difficult in the presence of a coexisting posterior chamber IOL. The technique reported allows a controlled conversion from posterior to anterior segment surgical techniques that may aid in either the removal or repositioning of posteriorly dislocated lens implants.

Aged↗

[Combined method of treating dislocated fractures of the calcaneus].

PURPOSE OF THE STUDY: The treatment of dislocated intraarticular fractures of calcaneus is still an unsolved chapter of traumatology. Our own poor long-term results of a purely conservative procedure has led us to develop a combined method of a direct and indirect reduction of calcaneus with the subsequent stabilization which we have been using since 1994. The basic principle of the method consists in the combination of a direct reduction of dislocated fragments of articular surfaces and indirect of calcaneus as a whole with the subsequent transfixation of calcaneus by K-wires. MATERIAL: In the period of 1994-2001 we have treated in total 261 patients with 302 fractures of calcaneus, of which 218 were men (83.5%) and 43 women (16.5%) in the age range from 13 to 82 years (average age 45.1 years). By our own surgical method we treated 213 patients with 248 fractures, of which 180 were men (84.5%) and 33 women (15.5%) in the age range of 13-79 years (average age 44.8 years). Conservatively handled were 54 fracture in 48 patients. In the long-term followed up group we included 160 patients with 187 fractures operated on by identical method observing a minimum two-year interval after the operation. Of them 134 were men (83.8%) and 26 women (16.2%) in the age range of 15-75 years (average age 44.3 years). Of 248 operated on fractures of calcaneus 159 were joint-depression type (64.1%), 61 tongue type (24.6%) and 28 comminuted (11.3%) types of fractures. The time interval between the injury and operation ranged between 6 hours and 3 weeks (average 18.5 hours), however most patients we operated on on the day of injury. METHODS: The basic principle of the method was a combination of a direct reduction of dislocated fragments of articular surfaces and indirect reduction of the calcaneus as a whole with a subsequent transfixation of the calcaneus by K-wires. After draping and setting of the image intensifier we proceeded to the actual surgery and divided the whole procedure of reduction and subsequent stabilization into 4 phases: Phase I--traction Phase II--elevation Phase III--compression Phase IV--transfixation In the first traction phase we inserted K-wire transversely through the distal-posterior edge of the calcaneus and connected it to the U-handle in order to achieve a proper effect of the traction. By traction distally along the long axis of the limb we restored the height and length of the calcaneus. Simultaneous pendular movements in eversion/inversion direction released the fragments and considerably facilitated the subsequent reduction. In the second, elevation phase the procedure differed according to individual types of fracture. In joint-depression type we inserted a blunt Steinmann pin or better a curved transpedicular elevator under the dislocated posterior articular surface through skin plantar stab incision and an ever-present primary transverse line of the fracture. In the tongue type of fracture we first introduced in the second phase a thick K-wire (3 mm) along the long axis of the tongue fragment and reduce the fragment by leverage elevation with a simultaneous continuous U-handle traction. After obtaining the desirable position we fixed the fragment by a K-wire vertically introduced from the upper part of calcaneal tuberosity (anteriorly and laterally from the origin of the Achilles tendon) towards the planta. If the medial part of the posterior articular surface remained dislocated we finished its reduction by means of elevator as in the preceding type of the fracture. The third and fourth phases of the surgical procedure was again identical for both types of fractures. In the third, compression phase we performed manually lateral compression of fragments under permanent traction. In the fourth, transfixation phase we first transfixed the reduced position of fragments formed by the primary longitudinal and transverse line. Under continuous radiograph checking in the lateral projection we inserted K-wires gradually from the lateral aspect, about 1.5 cm beneath the lateral malleolus into sustentacular fragment. Additional, mostly 2 K-wires we inserted under continuous traction and counter-traction along the long axis of the calcaneus and as the last step we drilled K-wires from the plantar side from calcaneal tuberosity into the fragments of the posterior articular surface. RESULTS: In the group of long-term followed up patients we evaluated the Creighton-Nebraska Health Foundation score in 160 patients who were on average 43.4 months after operation. The obtained values of the score ranged between 63-100 points with the average of 83.9 points. In 27 patients the result was very good (16.9%), in 89 patients good (55.6%), in 24 patients fair (15.0%) and in 20 patients the result was poor (12.5%). DISCUSSION: The first results of our method of 1998 have proved that it is necessary to combine the basic procedures of direct reduction of joint fragments, i.e. restoration of the calcaneus as a whole, namely in a strictly recommended sequence with a subsequent transfixation by K-wires. We do not use surgical procedures with open reduction and internal fixation (ORIF) differing mutually by the chosen surgical approach and the type of internal fixation used. As compared to ORIF our method has a significantly broader indication range. It can be used for the operation of patients regardless of the age, presence of associated diseases (diabetes, vascular affection) or local affection (a marked oedema, haematoma, non-infected skin blisters). The comparison of the general outcomes of the treatment in our group of patients, 72.5% of excellent and good results and only 12.5 of poor results, corresponds with the values of equally extensive foreign group of patients. In addition, as concerns the number of the incidence of deep infects in closed fractures (0.8%) the values in our group are in comparison several times lower and amputation of the limb was not necessary in any of the cases. It should be also noted that our group of patients has only a minimal indication limitation and operated on are also risk patients who never get in "filtered" groups treated by open method. Therefore it may be stated that the general results are in case of our method markedly better. CONCLUSION: The proposed method requires neither a specialist nor any expensive technical equipment and as a result it may be used both at orthopaedic and surgical departments and due to its undemanding nature and short hospitalization it is also very acceptable from the economic viewpoint.

Adolescent↗

[Management of posteriorly dislocated lenses: a report on 18 cases].

The posterior dislocation of the lens is a relatively frequent complication of ocular trauma. Treatment is medical, surgical and optical. The authors present a retrospective study of 18 patients (18 eyes) operated between January 1990 and December 1999 for a posterior dislocation of the lens. The age of the patients varied from 9 to 60 years, with a mean of 46 years. The etiology of the dislocation was an eye contusion in 15 cases and spontaneous dislocation in 3 cases. Vitrectomy was performed in all the patients, followed by extraction of the lens using one of two methods Results were good in both groups, with a final visual acuity better than 1/10 in 11 cases out of 18. Complications were substantially fewer than when using old techniques and included 4 cases of hypertonia, 3 cases of corneal edema, 2 cases of retinal detachment, and 1 case of macular edema. All of these complications were treated medically and/or surgically. The authors discuss the advantages and disadvantages of all lens extraction techniques and the benefits of the use of perfluorocarbon liquid in the treatment of the dislocated lens.

Adolescent↗

[Clinical retrospect on autoimplantation of traumatically dislocated teeth].

OBJECTIVE: A total of 48 cases with autoimplantation of traumatically dislocated teeth were retro spected as clinical references. METHODS: Several indexes were recorded in details, for instance, tooth dislocation time, operation and postoperative management and patients were followed up periodically. RESULTS: Tooth dislocating intervals from trauma to implantation were from 0.5 to 48 hours. Therapeutic effectiveness was graded as perfect in 37 teeth (61.7%), good in 18 (30.0%) and poor in 5 teeth (8.3%), in which 3 teeth were extracted within 1 year. Three-year success rate was 83.0%, and five-year success rate was 61.7%. It was judged 20 teeth being as periodontal membranous healing, 35 bony healing and 5 fibrous healing. Pulpal vitality tests were positive in 23 and negative in 37 teeth. Root canal therapies were conducted in 20 teeth. CONCLUSION: Carefully protecting periodontal membranes, keeping good fixation, preventing from infection and avoiding occlusal injuries are important factors for successful implantation of the dislocated teeth. Periodical examination would be benefit to the long term prognosis. The correct methods for dislocated tooth preservation should be treated as the important part of health education.

Adolescent↗

The alterations in adenosine nucleotides and lactic acid levels in striated muscles following death with cervical dislocation or electric shock.

In this study, changes in adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and lactic acid levels in masseter, triceps, and quadriceps muscles obtained from right and left sides of Spraque-Dawley rats following two different types of death were investigated. The samples were taken immediately and 120 minutes after death occurred either by cervical dislocation or electric shock. ATP concentrations in the muscles of masseter, triceps, and quadriceps were lower in samples obtained 120 minutes after death than that of samples obtained immediately after death. ADP, AMP, and lactic acid concentrations in these muscles were higher in samples obtained 120 minutes after death than those obtained immediately after death. A positive linear correlation was determined between ATP and ADP concentrations in quadriceps muscles of the rats killed with cervical dislocation and in masseter muscles of the rats killed with electric shock. When the rats killed with cervical dislocation and with electric shock were compared, ADP, AMP, and lactic acid concentrations were lower in the former than in the latter for both times (immediately and 120 minutes after death occurred). In the case of electric shock, ATP is consumed faster because of immediate contractions during death, resulting in a faster rigor mortis. This finding was confirmed with higher lactic acid levels in muscles of the rats killed with electric shock than the other group. In the cervical dislocation and electric shock group rats, ATP decreased in different levels in the three different muscle types mentioned above, being much decline in masseter in cervical dislocation and in quadriceps in electric shock group. This may be caused by low mass and less glycogen storage of masseter and by near localisation of electrode to quadriceps. One can conclude that the occurrence of rigor mortis is closely related to the mode of death.

Adenine Nucleotides↗