Central Dislocation Research Articles

Dislocation interactions in γ-channels between γ′-particles of superalloy single crystals

In the present work, a discrete dislocation model (DDM) is used to study interactions of γ-channel dislocations in γ/γ′-microstructures of superalloy single crystals. The study considers three types of γ-channels, 12 (isolated) octahedral face centered cubic slip systems and two macroscopic crystallographic shear-loading conditions. It was found that different types of γ-channels vary with respect to the number of dislocations, which can enter the channels. This effect becomes more important in the presence of misfit stresses. Misfit stresses were integrated into the present analysis by performing preliminary thermoelastic misfit stress calculations, which served as one input for the calculation of the overall stress state. The two other input elements to the overall stress state are the stresses associated with external loading and the dislocation stress fields. The effect of the overall stress state is evaluated considering the Peach–Koehler force, which acts on a central channel dislocation. The results of the study demonstrate that it is not enough to discuss dislocation plasticity in γ/γ′-microstructures merely on the basis of external resolved shear stresses. It was shown that misfit stresses, which attract dislocation loops from one microscopic crystallographic slip system into one type of γ-channel make it more difficult for the same dislocations to enter other γ-channels.

Acetabular fractures in children and adolescents.

A retrospective study of 29 acetabular fractures in children 2 to 16 years of age with an average followup of 14 years is presented. Nineteen patients had an additional dislocation of the femoral head and 14 patients had an associated neurologic injury. Surgical treatment was performed in 16 patients and consisted of open reduction and internal fixation in 14 patients and a simple arthrotomy in two patients. Thirteen patients were treated nonoperatively with traction or bedrest. The outcome was satisfactory in all patients with undisplaced fractures and fractures with disruption of a small fragment. Eight patients with linear fractures with instability all were treated surgically. All but one of the patients had a satisfactory functional outcome; one patient had early degenerative changes develop after an open pelvic and acetabular fracture. Patients with central fractures and dislocations had a relatively poor outcome, and congruency was achieved in only one of the four patients who were treated surgically. Results may deteriorate with time, as was seen when the results of the current study were compared with those published 10 years previously.

Long term results of surgical therapy in acetabular fractures

Objectives: This study was designed to evaluate long term results and to determine prognostic factors in patients who underwent surgery for acetabular fractures. Methods: Of three hundred and thirty-two patients who underwent surgery for acetabular fractures between January 1970 and January 1998, 240 patients (186 males, 54 females; mean age 17 years; range 15-81 years) with adequate follow-up data were included. The mean period between the traumatic event and the last follow-up examination was 11.2 years (range 2-26 years). According to the classification of Letournel and Judet, 163 fractures (68%) were simple and 77 (32%) were of compound type. Central, posterior, and anterior dislocations occurred in 45.8%, 38.4%, and 15.8% of fractures, respectively. Results: At the last follow-up examination, excellent, good, fair, and poor functional results were obtained in 96 (40%), 96 (40%), 12 (5%), and 36 (15%) patients, respectively. Radiologic results were excellent in 45%, good in 21.7%, fair in 18.3%, and poor in 15%. Statistical analyses revealed that significant prognostic factors included mean period between the trauma and operation (p=0.05), damage to the femoral head (p=0.01), and the quality of anatomic reduction (p=0.009). Conclusion: We obtained satisfactory results in 192 of 240 hips (80%) by surgical therapy, aiming an excellent anatomic reduction in order to prevent late secondary osteoarthrosis. Similar results are reported in the literature by experienced surgical teams after long follow-up periods. Both in our series and in some other in the literature, no statistical significance between clinical and radiologic results have been found.

Open pelvic fractures with vaginal laceration: an unusual clinical feature

A 71-year-old female was admitted to casualty having been struck by a van while crossing a road. Examination revealed bleeding per vaginam and although she had no external injuries, palpable subcutaneous emphysema in the lower abdomen was detected. Roentgenograms con®rmed bilateral fractured ribs, a closed fracture of the right humerus, an extra capsular fracture of the right femur and a complex fracture of the pelvis with central dislocation of the left hip and bilateral superior and inferior pubic rami fractures. There was no evidence of a pneumothorax. A computerised tomographic scan (CT) scan of the patient's abdomen and pelvis, at 1 h post admission, showed extensive subcutaneous and intrapelvic emphysema (Figs. 1 and 2). Bowel perforation was suspected and an emergency laparotomy was performed after haemodynamic stabilisation. During the operation retroperitoneal and pelvic haematomas were noted but there was no evidence of bowel injury. Sigmoidoscopy was normal and a formal vaginal examination, deferred due to pain until general anaesthesia, revealed a vaginal tear in the right lateral wall measuring approx. 7 cm. This was repaired. The patient's orthopaedic injuries including the pelvic fracture were internally ®xed at a later date and she made a full recovery eventually.

Dynamics of self-trapped beams with phase dislocation in saturable Kerr and quadratic nonlinear media

We present a detailed stability analysis of one- and two-ring solitary waves with central phase dislocation in self-focusing saturable and quadratic nonlinear media. Varying parameters, we demonstrate transitions between different filamentation scenarios. An analytical approach is developed for the study of filament dynamics after ring breakup. Approximate expressions for the angular separation rate of filaments based on the conservation of the angular momentum and on the conservation of the Hamiltonian are derived and compared. The stability analysis and analytical results are tested by an extensive series of numerical simulations of the original models, and good agreement is found. @S1063-651X~98!14609-3#

AFM observation of barium nitrate {1 1 1} and {1 0 0} faces: : spiral growth and two-dimensional nucleation growth

The growth mechanisms of the {1 1 1} and {1 0 0} faces of Ba(NO 3) 2 crystals growing from aqueous solutions were investigated by ex situ atomic force microscopy. Growth hillocks induced by dislocations and growth islands formed via 2D nucleation were observed on both faces. The thinnest steps observed on the {1 1 1} and {1 0 0} faces were, irrespective of step sources, d 1 1 1 =4.7 Å and d 2 0 0 =4.1 Å in height, respectively. These correspond to the elementary growth layers expected in Bravais–Friedel–Donnay–Harker (BFDH) and Hartman–Perdok (i.e. periodic bond chain) theories. The spiral hillocks on the {1 0 0} face consist of double elementary layers. On {1 1 1} faces, three kinds of spiral layers arising from single dislocations were discerned: single, double and triple elementary layers, which can be produced by dislocations with Burgers vectors b =〈1 0 0〉, 〈1 1 0〉 and 〈1 1 1〉, respectively. It was observed that the multiple spiral layers tend to split into elementary steps at the spiral centres, which can be explained by entropic repulsion. It was also found that several spiral centres are accompanied with hollow cores and that the diameters of these cores vary with the number of spiral arms connected with the central dislocation. The numerous 2D nuclei of elementary height found between the spiral arms were probably created in the short period of very high supersaturation during separation of the crystal from the solution.

Simultaneous bilateral fractures of the hip following a grand mal seizure. An unusual complication

Pathological fractures as a consequence of convulsive seizures without direct trauma occur in 0.3% of cases. Some lesions such as bilateral posterior dislocation of the shoulder, fracture-dislocation of the shoulder or fracture and/or dislocation of the hip strongly suggest a seizure as the aetiology. We report on a patient with simultaneous central dislocation of one hip with fracture of the contralateral femoral neck provoked by spontaneous seizures. Unrecognized associated injuries following a convulsion may result in long-term functional disability and legal consequences.

Bilateral Central Acetabular Fracture Dislocations Secondary to Sustained Myoclonus

This case report presents a patient with bilateral central acetabular fracture dislocations secondary to sustained myoclonus treated with delayed bilateral total hip arthroplasty. This is an unusual mechanism of injury, but is similar to other uncontrolled muscular contractions, such as electroconvulsive therapy and seizures. Because of ongoing myoclonus, the patient initially was treated nonoperatively. The patient then successfully had staged bilateral total hip arthroplasty 15 months after injury. This case exemplifies that forceful, uncontrolled muscular contraction can cause bilateral symmetric fracture dislocations. In patients with a history of seizure or myoclonic contracture with subsequent pain or loss of function, radiographs are indicated and skeletal fracture or joint dislocation must be ruled out. Secondary reconstruction can be recommended when the patient is medically stable.

Extradural haematoma following intrauterine trauma

A rare case of a neonatal extradural haematoma following intrauterine trauma is described. Following a road traffic accident a 39 week pregnant mother sustained a central dislocation of the head of the femur. Pelvis radiographs revealed a skull fracture in the baby who, after delivery by Casesarian section, was in a poor neurological state. An extradural haematoma was demonstrated by early computed tomography. Immediate decompression by needle aspiration of the extradural space was followed by a craniotomy and evacuation of the haematoma. The child at 5 months old has no evidence of neurological sequelae and has reached normal developmental milestones.

Small bowel entrapment in a pubic ramus fracture: a cautionary tale

Entrapment of small bowel is a rare complication of displaced fractures of the pelvis. It was originally described by Arnold in 1907 in a 76year-old female with a displaced pelvic brim fracture who developed a small bowel perforation caused by entrapment within the fracture site. Recently it has also been described complicating a central fracture dislocation of the hip joint (Bacarese-Hamilton and Bhamra, 1991). These injuries may present diagnostic difficulties because the subsequent development of mechanical obstruction may be mistaken for paralytic ileus which is common after pelvic fractures due to the formation of retroperitoneal haematoma. We have recently managed a case of small bowel entrapment in a pubic ramus fracture which appeared to be minimally displaced at the time of initial radiographic assessment, and presented difficulties of both diagnosis and management.

Femoral shaft fractures complicated by fracture-dislocations of the ipsilateral hip.

A series of 16 consecutive adults with femoral shaft fractures complicated by fracture-dislocations of the ipsilateral hip joint was prospectively studied. There were 11 posterior dislocations and five central dislocations. The treatment consisted of early closed reduction of the dislocation with the assistance of an external fixator, delayed reamed intramedullary nailing of the femoral fracture, and conservative or surgical treatment of the hip joint according to the indications. The follow-up period was 2-8 years (median, 3.5 years). Although an 18.8% (3 of 16) complication rate was noted, the outcome was satisfactory for all 16 hip joints. When such complicated combined injuries are sustained, the technique described here is the most reasonable treatment.

Central Fracture-Dislocation of the Hip with Ipsilateral Femoral Neck Fracture

Central fracture dislocation of the hip with associated fracture of the femoral neck is rare. Treatment of choice consists of open reduction of the displacement and internal fixation of both fractures. Nevertheless, inadequate reduction of the burst fracture of the acetabulum may lead to hip arthritis, and the surgical approach to the femoral neck jeopardizes its vitality. In elderly patients early full motion and prompt physical rehabilitation can be achieved by total hip arthroplasty after fusion of the displaced femoral head to the acetabular wall.

Injury to the external iliac artery during hip arthroplasty for old central dislocation

Injury to a major vessel is an uncommon but well recognized and serious complication of total hip arthroplasty. An increased risk of such injury has been reported in rheumatoid patients, in revision surgery, and with the injudicious use of particular instruments, especially the sharp Hohmann retractor. The authors report the case of a patient who sustained a laceration to his external iliac artery during the course of a hip arthroplasty for osteoarthritis secondary to old central dislocation. The cause of the injury is discussed and the relevant literature reviewed.

Occult Central Acetabular Fracture Resulting in Fracture-Dislocation A Case Report

A 71-year-old white female experienced a nondisplaced right central acetabular fracture in a motor vehicle accident. Despite anteroposterior (AP) roentgenograms of the pelvis, Judet views, and plain tomograms, no fracture was detected. These negative findings did not entirely explain the continued presence of pain. The patient was treated with physical therapy and encouraged to bear weight on the leg as tolerated. The fracture then progressed to a central fracture dislocation readily apparent on AP views of the pelvis. This case illustrates the need for further diagnostic studies (bone scanning, computed tomography, and magnetic resonance imaging) when, despite negative objective findings, a high degree of suspicion persists.

Chronic unreduced dislocations of the glenohumeral joint: imaging strategy and pathologic correlation.

Although the evaluation of acute or recurrent dislocations of the glenohumeral joint (GHJ) using routine radiography, specialized views, arthrography, and computed tomography (CT) has been extensively studied, methods of evaluation and osseous pathology of chronic unreduced GHJ dislocations are not well documented. In order to define such methods and pathology, we studied nine patients with chronic (greater than 6 months) unreduced anterior, posterior, superior, or central dislocations as well as one patient with a chronic rotator cuff injury; and seven scapular specimens, six with matching humeral specimens, with osseous abnormalities similar to those in the patients. We examined 15 additional scapular specimens with evidence of subluxation secondary to chronic rotator cuff injury. Standard, reformatted, and three-dimensional (3D) CT techniques were used to evaluate both the patients and the specimens. Our results indicate that characteristic alterations occur in the scapula and humeral head that are far more extensive than the classic Hill-Sachs, Bankart, and trough lesions. Such alterations occur at sites of osseous contact between the malpositioned humerus and scapula and are modified owing to prolonged adjustments made by the patients in an attempt to increase GHJ motion. Although routine radiography and specialized views are of some value, standard and 3D CT provide a more accurate analysis of the location and extent of the bone abnormalities and, as such, should be employed, particularly in the evaluation of patients in whom surgery is being considered.

On isolated lamellae of melt-crystallized polyethylene

The growth, isolation and examination of individual melt-grown crystals of linear polyethylene is reported. Monolayers grown at 130°C have continuously curved elliptic prism faces (despite being grown under ‘regime I’ conditions) and fold surfaces close to {2 0 1}. Such monolayers, showing a sector boundary along their length, and distinct sectors differing very slightly in orientation across this boundary, have been revealed in dark-field electron microscopy. This is evidence for regularity in chain folding. A more frequent form is when a central screw dislocation is present near the centre of a lamella. The spiral terrace developing from this shows a remarkable habit in which adjacent layers splay apart, but growth soon stops, leaving the upper and lowermost layers plano-convex in outline. In every case, the planar outline is of a prism face making an acute angle with the previous layer. This is a consequence of growth having only occurred around screw dislocations of the appropriate hand: right-handed for a (201) surface. It is suggested that this habit, illustrating how spiral development selects screw dislocations of a consistent hand, may be the missing element in understanding the growth of banded spherulites in polyethylenes via systematic arrays of similar screw dislocations.

Cullen's sign: a new association with central dislocation of the hip joint

Cullen's sign: a new association with central dislocation of the hip joint

Distribution and severity of injuries associated with hip dislocations secondary to motor vehicle accidents.

The injuries associated with traumatic hip dislocations and their quantitated morbidities were evaluated in this retrospective study of 38 patients. Ninety-five per cent of the patients had associated injuries severe enough for hospitalization on their own merit. Head, chest, and abdominal injuries were seen most frequently. Central dislocations were associated with the most morbidity, but were not different in distribution of injuries. Using eight different measurements of morbidity, including the Injury Severity Score, hip dislocations, in general, had more morbidity than the national injury rates.

Mandibular condyle fracture and dislocation into the middle cranial fossa

A case report is presented concerning a patient who sustained a condyle fracture with superior dislocation into the middle cranial fossa. Although relatively rare, other cases of central condylar dislocation have been presented and will be discussed and compared. Diagnosis has been a problem, and treatments have varied greatly for these cases. This is the first case on record, however, in which such a dislocation occurred in conjunction with a fracture of the condylar head. In the present case, the dura was covered with temporalis muscle and the glenoid fossa was covered using the fragments of the fractured condyle as an autogenous free bone graft.

Central luxation or dislocation of the mandibular condyle into the middle cranial fossa. A case report and review of the literature

Abstract This case report concerns a central luxation of the mandibular condyle of an 11-year-old girl. After a fall from a bicycle, the mandibular condyle luxated into the middle cranial fossa. The mandible was “ankylosed” in an ipsilateral latero-occlusion, and the diagnosis was confirmed by temporomandibular joint radiography. Immediate conservative reposition was performed successfully, without any immobilisation. After 18 months follow-up, the temporomandibular joint function was normal and painless despite progressive degenerative changes in the mandibular condyle. The patient's facial appearance proved to be normal.