Dissociation of edge and screw pyramidal Ⅰ and Ⅱ dislocations in magnesium

Pyramidal dislocations in magnesium (Mg) and other hexagonal close-packed metals play an important role in accommodating plastic strains along the c-axis.Bulk single crystal Mg only presents very limited plasticity in c-axis compression,and this behavior was attributed to out-of-plane dissociation of pyramidal dislocations onto the basal plane and resulted in an immobile dislocation configuration.In contrast,other simulations and experiments reported in-plane dissociation of pyramidal dislocations on their slip planes.Thus,the core structure and mode of dissociation of pyramidal dislocations are still not well understood.To better understand the dissociation behavior of pyramidal dislocations in Mg at room temperature,in this work,atomistic simulations were conducted to investigate four types of pyramidal dislocations at 300 K:edge and screw Py-Ⅰ on{1011},edge and screw Py-Ⅱ on{1122}by using a modified embedded atom method (MEAM) potential for Mg and anisotropic elasticity dislocation model.The results show that when energy minimization was performed before relaxation,in-plane dissociation of edge dislocations on respective pyramidal plane could be obtained at room temperature for all four types of dislocation.Without energy minimization,the edge dislocations dissociated out-of-plane onto the basal plane.Calculations of potential energy and hydrostatic stress of individual atoms at the edge dislocation core show that the extraordinarily high energy and atomic stresses in the as-constructed dislocation structures caused the out-of-plane dissociation onto the basal plane.The core structures of all four types of pyramidal dislocation after in-plane dissociation were analyzed by computing the distribution of the Burgers vector.

Posterior pedicle screw fixation combined with local steroid injections for treating axial eosinophilic granulomas and atlantoaxial dislocation:A case report

BACKGROUND Eosinophilic granuloma(EG)is a proliferative condition that affects the cells of bone tissue.There are no specific clinical signs or imaging manifestations in the early stages of the disease,making it simple to overlook and misdiagnose.Because of the disease's rarity,there is presently no standardized treatment principle.There are few accounts of such occurrences affecting the axis among children.We discovered a case of a child whose EG resulted in atlantoaxial joint dislocation and destruction of the axial bone.CASE SUMMARY After having pharyngeal discomfort for more than six months without a clear explanation,a 6-year-old boy was brought to our hospital.Following a careful evaluation,the pathology indicated a strong likelihood of an axial EG.Ultimately,we decided to treat the boy with posterior pedicle screw fixation and local steroid injections.CONCLUSION EGs of the upper cervical spine are quite uncommon in children,and they are exceedingly easy to overlook or misdiagnose.Posterior pedicle screw fixation and local steroid injections are effective treatments for patients with axial EGs affecting the atlantoaxial junction.

C1C2 Wiring and Posttraumatic Atlantoaxial Dislocation: An Effective and Cheap Surgical Procedure in a Developing Country

Objectives: Atlantoaxial dislocation remains a rare and serious condition with a high preoperative and postoperative morbidity and mortality. Its successful surgical management is still challenging and gratifying for neurosurgeons. Several technics have been described such as wiring, trans articular screwing, C1C2 screwing with plate and screw introduced by Goel et al., and modified by insertion of polyaxially screw and rod many years later by Harms. Unavailability and expensiveness of upper cervical spine instrumentation device led us to C1C2 Wiring resulting in a good outcome. Finally, a quadriplegic patient with a more comfortable financial condition had ordered devices from abroad and benefit for Goel and Harms screwing technique and improved dramatically from ASIA A to ASIA E. Material and methods: This is a retrospective study of patients managed in our department by a same neurosurgeon from January 2019 to April 2024. Results: We defined 6 men and 1 woman with an average age of 33 years. Unrestrained driver in a rollover motor vehicle accident was most common. Only one patient was neurologically intact on admission. Neurovegetative disorders were noticed in one patient. Dislocation was associated to a fracture of the dens in two patients. Three patients have been successfully operated with remarkable outcome, mostly from ASIA A to E. Conclusion: C1C2 dislocation is a serious condition and C1C2 Wiring represents an effective and cheaper technic. Therefore, this technic should deserve consideration above all in low incomes countries when screwing devices are not available. Seatbelt should be demanded for motor vehicle drivers and passengers.

Additive manufactured osseointegrated screws with hierarchical design

Bone screws are devices used to fix implants or bones to bones.However,conventional screws are mechanically fixed with thread and often face long-term failure due to poor osseointegration.To improve osseointegration,screws are evolving from solid and smooth to porous and rough.Additive manufacturing(AM)offers a high degree of manufacturing freedom,enabling the preparation of predesigned screws that are porous and rough.This paper provides an overview of the problems currently faced by bone screws:long-term loosening and screw breakage.Next,advances in osseointegrated screws are summarized hierarchically(sub-micro,micro,and macro).At the sub-microscale level,we describe surface-modification techniques for enhancing osseointegration.At the micro level,we summarize the micro-design parameters that affect the mechanical and biological properties of porous osseointegrated screws,including porosity,pore size,and pore shape.In addition,we highlight three promising pore shapes:triply periodic minimal surface,auxetic structure with negative Poisson ratio,and the Voronoi structure.At the macro level,we outline the strategies of graded design,gradient design,and topology optimization design to improve the mechanical strength of porous osseointegrated screws.Simultaneously,this paper outlines advances in AM technology for enhancing the mechanical properties of porous osseointegrated screws.AM osseointegrated screws with hierarchical design are expected to provide excellent long-term fixation and the required mechanical strength.

Biomechanical effects of posterior lumbar interbody fusion with vertical placement of pedicle screws compared to traditional placement

BACKGROUND The pedicle screw technique is widely employed for vertebral body fixation in the treatment of spinal disorders.However,traditional screw placement methods require the dissection of paraspinal muscles and the insertion of pedicle screws at specific transverse section angles(TSA).Larger TSA angles require more force to pull the muscle tissue,which can increase the risk of surgical trauma and ischemic injury to the lumbar muscles.AIM To study the feasibility of zero-degree TSA vertical pedicle screw technique in the lumbosacral segment.METHODS Finite element models of vertebral bodies and pedicle screw-rod systems were established for the L4-S1 spinal segments.A standard axial load of 500 N and a rotational torque of 10 N/m were applied.Simulated screw pull-out experiment was conducted to observe pedicle screw resistance to pull-out,maximum stress,load-displacement ratio,maximum stress in vertebral bodies,load-displacement ratio in vertebral bodies,and the stress distribution in pedicle screws and vertebral bodies.Differences between the 0-degree and 17-degree TSA were compared.RESULTS At 0-degree TSA,the screw pull-out force decreased by 11.35%compared to that at 17-degree TSA(P<0.05).At 0-degree and 17-degree TSA,the stress range in the screw-rod system was 335.1-657.5 MPa and 242.8-648.5 MPa,separately,which were below the fracture threshold for the screw-rod system(924 MPa).At 0-degree and 17-degree TSA,the stress range in the vertebral bodies was 68.45-78.91 MPa and 39.08-72.73 MPa,separately,which were below the typical bone yield stress range for vertebral bodies(110-125 MPa).At 0-degree TSA,the load-displacement ratio for the vertebral bodies and pedicle screws was slightly lower compared to that at 17-degree TSA,indicating slightly lower stability(P<0.05).CONCLUSION The safety and stability of 0-degree TSA are slightly lower,but the risks of screw-rod system fracture,vertebral body fracture,and rupture are within acceptable limits.

Elbow Dislocation in Children: About Two Cases and Review of the Literature

Background: Elbow dislocations in pediatric patients are rare injuries. This is a therapeutic emergency because a delay in treatment can have disastrous consequences on the functional level of the upper limb. Objective: To present the management of elbow dislocation in children in cases of limited resources. Presentation of the Cases: These were 2 older male children aged 7 and 9 years old, admitted to the emergency room for painful functional impotence of the right elbow after a fall and landing on the right hand. Clinical and radiological examinations were in favor of posterior elbow dislocations. The reductions were carried out under sedation and immobilization in Jersey. According to Robert’s criteria, the functional result was excellent in both patients. Conclusion: Emergency reduction and immobilization whatever the means ensure an excellent functional prognosis even in cases of limited resources.

Roughness characterization and shearing dislocation failure for rock-backfill interface

Shearing dislocation is a common failure type for rock–backfill interfaces because of backfill sedimentation and rock strata movement in backfill mining goaf.This paper designed a test method for rock–backfill shearing dislocation.Using digital image techno-logy and three-dimensional(3D)laser morphology scanning techniques,a set of 3D models with rough joint surfaces was established.Further,the mechanical behavior of rock–backfill shearing dislocation was investigated using a direct shear test.The effects of interface roughness on the shear–displacement curve and failure characteristics of rock–backfill specimens were considered.The 3D fractal dimen-sion,profile line joint roughness coefficient(JRC),profile line two-dimensional fractal dimension,and the surface curvature of the frac-tures were obtained.The correlation characterization of surface roughness was then analyzed,and the shear strength could be measured and calculated using JRC.The results showed the following:there were three failure threshold value points in rock–backfill shearing dis-location:30%–50%displacement before the peak,70%–90%displacement before the peak,and 100%displacement before the peak to post-peak,which could be a sign for rock–backfill shearing dislocation failure.The surface JRC could be used to judge the rock–backfill shearing dislocation failure,including post-peak sliding,uniform variations,and gradient change,corresponding to rock–backfill disloca-tion failure on the field site.The research reveals the damage mechanism for rock–backfill complexes based on the free joint surface,fills the gap of existing shearing theoretical systems for isomerism complexes,and provides a theoretical basis for the prevention and control of possible disasters in backfill mining.

Comparison of Surgical Techniques Used in Treating Acromioclavicular Dislocation in Patients Participating in Sports: A Systematic Review

Introduction: The acromioclavicular joint is a superficial diarthrodial joint that surrounds the medial articular facet of the acromion and the distal portion of the clavicle. Due to its anatomy and biomechanics, it is highly susceptible to trauma and in young men who play contact sports, acromioclavicular dislocation is common. This article aimed to systematically review the literature and compare the surgical techniques used in the treatment of acromioclavicular dislocation in patients who practice sports. Methods: This systematic review was conducted according to the International Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines. Eligible studies for this systematic review included articles in English or Spanish published between 2013 and 2023, which mention the occurrence of acromioclavicular dislocation during sports practices. Additionally, only studies that addressed the surgical treatment of acromion-clavicular dislocation and contained original data on the topic were included. Results: We found 144 eligible studies after searching the LILACS and PubMed databases. Based on the inclusion and exclusion criteria and the reviewers’ consensus, we selected four studies for the systematic review. 133 patients with AC joint displacement were evaluated. Mean Age: approximately 31.90 years. 81.92 of these injuries occurred during sports practice. Surgical Procedures Used: titanium plates fixation (49 patients), arthroscopy (24), single tunnel technique (30) and coracoid sling technique (30). The results of the visual analog scale and Constant-Murley scores varied between the techniques used. Twenty-two complications after surgical treatment were identified. Conclusion: A significant variability of operative techniques can be used in the surgical approach of acromioclavicular dislocation, such as arthroscopy, single tunnel, coracoid sling and titanium plates. Although it presented excellent functional results compared to the other three techniques evaluated by this review, using titanium plates is not the gold standard since other techniques not assessed by this work may be more effective.

Micropillar compression using discrete dislocation dynamics and machine learning

Discrete dislocation dynamics(DDD)simulations reveal the evolution of dislocation structures and the interaction of dislocations.This study investigated the compression behavior of single-crystal copper micropillars using fewshot machine learning with data provided by DDD simulations.Two types of features are considered:external features comprising specimen size and loading orientation and internal features involving dislocation source length,Schmid factor,the orientation of the most easily activated dislocations and their distance from the free boundary.The yielding stress and stress-strain curves of single-crystal copper micropillar are predicted well by incorporating both external and internal features of the sample as separate or combined inputs.It is found that the machine learning accuracy predictions for single-crystal micropillar compression can be improved by incorporating easily activated dislocation features with external features.However,the effect of easily activated dislocation on yielding is less important compared to the effects of specimen size and Schmid factor which includes information of orientation but becomes more evident in small-sized micropillars.Overall,incorporating internal features,especially the information of most easily activated dislocations,improves predictive capabilities across diverse sample sizes and orientations.

Dislocation of primary total hip arthroplasty:Analysis of risk factors and preventive options

Total hip arthroplasty(THA)is one of the most successful elective operations in orthopedic surgery for improving pain and functional disability in patients with end-stage joint disease.However,dislocation continues to be a troublesome complication after THA,as it is a leading cause of revision and is associated with substantial social,health,and economic costs.It is a relatively rare,usually early occurrence that depends on both the patients’characteristics and the surgical aspects.The most recent and important finding is the special attention to be given preoperatively to spinopelvic mobility,which is closely related to the incidence of dislocation.Consequently,clinical and radiographic assessment of the lumbar spine is mandatory to identify an altered pelvic tilt that could suggest a different positioning of the cup.Lumbar spinal fusion is currently considered a risk factor for dislocation and revision regardless of whether it is performed prior to or after THA.Surgical options for its treatment and prevention include the use of prostheses with large diameter of femoral head size,dual mobility constructs,constrained liners,and modular neck stems.

Evaluation of Functional and Radiological Outcome of Arthroscopic-Assisted Anatomical Coracoclavicular (CC) and Acromioclavicular (AC) Ligament Reconstruction in Chronic AC Joint Dislocation

Introduction: Acromioclavicular (AC) joint dislocation is a common shoulder injury, comprising 9% - 12% of shoulder girdle injuries. Optimal management remains challenging, with treatment decisions guided by the Rockwood classification system. Controversies surround grade III injuries, necessitating further classification. Non-operative treatment has shown favorable outcomes, while surgical interventions vary. Anatomical coracoclavicular reconstruction (ACCR) has demonstrated biomechanical advantages over traditional methods. Arthroscopic techniques offer advantages, minimizing deltoid detachment and allowing concurrent pathology identification. This study evaluates the outcomes of arthroscopic-assisted ACCR in chronic AC joint dislocation. Surgical Technique: Arthroscopic-assisted ACCR involves meticulous portal placement, tendon graft harvesting, diagnostic arthroscopy, and coracoid exposure. The clavicle tunnels were made to mimic the conoid and trapezoid ligament positions, using FibreTape#2 loop and Dog Bone Button for correct placement against the coracoid base, and passing the semitendinosus graft through to reconstruct the conoid ligament, reduction done and graft follow through for anatomical reconstruction. Methods: A retrospective cohort study at Hospital Kuala Lumpur analyzed 35 patients undergoing arthroscopic-assisted ACCR for Rockwood grade III - V AC joint dislocations. Inclusion criteria encompassed trauma ≥ 3 weeks prior, no prior shoulder injuries, and ≥12-month follow-up. Functional and radiological assessments utilized ASES scores and coracoclavicular distances, respectively. Statistical analysis employed descriptive statistics and logistic regression. Results: The mean age was 38.9 years (SD 11.26), and 34 of 35 patients were male. Grade IV injuries were predominant (37.1%). Waiting time for surgery averaged 234.9 days. Functional improvement was substantial postoperatively (ASES: 55.5 to 88.9). Radiological outcomes demonstrated reduced coracoclavicular distances and maintained reduction. No significant correlation was observed between injury grade and outcomes. Conclusion: Arthroscopic-assisted ACCR for chronic AC joint dislocation yields significant functional and radiological improvement, irrespective of injury grade. Waiting time for surgery exhibits minor impact on outcomes, emphasizing the procedure’s efficacy. Concomitant injuries do not impede success, highlighting the versatility of this approach in managing shoulder instability. The study contributes valuable insights into the nuanced management of chronic AC joint dislocations and supports the adoption of arthroscopic-assisted ACCR as a viable treatment option.

Roller Screw and Threaded Chain Speed Reducer: An Experimental Evaluation

We are developing a speed reducer that can be considered a transformation of a worm gear reducer: the worm is replaced by an inverted roller screw, and the gear is replaced by a threaded chain drive. This configuration lessens wear, increases load capacity, and improves efficiency. The threaded chain consists of nut-shaped links. This paper presents the results of tests carried out on a prototype with a reduction ratio of 46.

Clinical Effectiveness of the Plate Screw Internal Fixation Technique in the Treatment of Patients with Traumatic Fractures of Long Bones in the Lower Extremities

Objective: To investigate the effectiveness of the plate screw internal fixation technique on the clinical outcomes of patients with traumatic fractures of long bones in the lower extremities. Methods: From January 2022 to December 2023, 70 patients with traumatic fractures of long bones in the lower extremities were admitted to the hospital and randomly divided into two groups: the control group and the observation group, each consisting of 35 cases. The control group underwent traditional closed interlocking intramedullary nailing, while the observation group received internal fixation with steel plates and screws. Relevant surgical indicators, treatment effectiveness, and postoperative complication rates were compared between the two groups. Results: The observation group exhibited significantly short surgical duration (80.65 ± 5.01 vs. 88.36 ± 5.26 minutes), fracture healing time (13.27 ± 0.32 vs. 15.52 ± 0.48 weeks), and hospitalization days (10.49 ± 1.13 vs. 16.57 ± 1.15 days) compared to the control group (P = 0.000). The effective treatment rate was significantly higher in the observation group (29/82.86%) than in the control group (21/60.00%), with a significant difference observed (χ2 = 4.480, P = 0.034). Additionally, the complication rate in the observation group (2/5.71%) was significantly lower than that in the control group (8/22.86%), with a correlated difference (χ2 = 4.200, P = 0.040). Conclusion: The plate screw internal fixation technique demonstrates significant clinical efficacy in treating traumatic fractures of long bones in the lower extremities. It improves the healing rate, reduces complications, and represents a safe and effective treatment strategy worthy of widespread use and application.

Interaction between a screw dislocation and an elastic elliptical inhomogeneity with interfacial cracks

The elastic interaction between a screw dislocation and an elliptical inhomogeneity with interfacial cracks is studied. The screw dislocation may be located outside or inside the inhomogeneity. An efficient complex variable method for the complex multiply connected region is developed, and the general solutions to the problem are derived. As illustrative examples, solutions in explicit series form for complex potentials are presented in the case of one or two interfacial cracks. Image forces on the dislocation are calculated by using the Peach-Koehler formula. The influence of crack geometries and material properties on the image forces is evaluated and discussed. It is shown that the interfacial crack has a significant effect on the equilibrium position of the dislocation near an elliptical-arc interface. The main results indicate, when the length of the crack goes up to a critical value, the presence of the interfacial crack can change the interaction mechanism between a screw dislocation and an elliptical inclusion. The present solutions can include a number of previously known results as special cases.

Interaction between many parallel screw dislocations and a semi-infinite crack in a magnetoelectroelastic solid

Based on the fundamental equations of magnetoelectroelastic material and the analytic theory, and using the Muskhelishvili-introduced well-known elastic techniques combined with the superposition principle, the closed form solution of the generalized stress field of the interaction between many parallel screw dislocations and a semi-infinite crack in an infinite magnetoelectroelastic solid is obtained, on the assumption that the surface of the crack is impermeable electrically and magnetically. Besides, the Peach-Koehler formula of n parallel screw dislocations is given. Numerical examples show that the generalized stress varies with the position of point z and is related to the material constants. The results indicate that the stress concentration occurs at the dislocation core and the tip of the crack. The result of interaction makes the system stay in a lower energy state.

Interaction between a screw dislocation and an elliptical hole with two asymmetrical cracks in a one-dimensional hexagonal quasicrystal with piezoelectric effect

The interaction between a screw dislocation and an elliptical hole with two asymmetrical cracks in a one-dimensional(1 D) hexagonal quasicrystal with piezoelectric effect is considered. A general formula of the generalized stress field, the field intensity factor, and the image force is derived, and the special cases are discussed. Several numerical examples are given to show the effects of the material properties and the dislocation position on the field intensity factors and the image forces.

Shielding effect and emission criterion of a screw dislocation near an interfacial blunt crack

Shielding effect and emission criterion of a screw dislocation near an interracial blunt crack are dealt with in this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex potentials and stress fields due to a screw dislocation located near the interracial blunt crack. The stress intensity factor on the crack tips and the critical stress intensity factor for dislocation emission are also calculated. The influence of the orientation of the dislocation and the morphology of the blunt crack as well as the material elastic dissimilarity on the shielding effect and the emission criterion is discussed in detail. The results show that positive screw dislocations can reduce the stress intensity factor of the interfacial blunt crack tip （shielding effect）. The shielding effect increases with the increase of the shear modulus of the lower half-plane, but it decreases with the increase of the dislocation azimuth angle. The critical loads at infinity for dislocation emission increases with the increase of emission angle and curvature radius of blunt crack tip, and the most probable angle for screw dislocation emission is zero. The present solutions contain previous results as special cases.

A SCREW DISLOCATION IN A THREE-PHASE COMPOSITE CYLINDER MODEL WITH INTERFACIAL RIGID LINES

The problem of the elastic interaction between a screw dislocation and a three-phase circular inclusion with interracial rigid lines （anti-cracks） is investigated. An efficient and concise method for the complex multiply connected region is developed, with which explicit series form solutions of the complex potentials in the matrix, and the interphase layer and inclusion regions are derived. Based on the complex potentials, the image force on the screw dislocation is then calculated by using the Peach-Koehler formula. The equilibrium position of the dislocation is discussed in detail for various rigid line geometries, interphase layer thicknesses and material property combinations. The main results show that the interracial rigid lines exert a significant perturbation effect on the motion of the screw dislocation near the circular inclusion surrounded by an interphase layer.

The interaction between a screw dislocation and a wedge-shaped crack in one-dimensional hexagonal piezoelectric quasicrystals

Based on the fundamental equations of piezoelasticity of quasicrystal material,we investigated the interaction between a screw dislocation and a wedge-shaped crack in the piezoelectricity of one-dimensional hexagonal quasicrystals.Explicit analytical solutions are obtained for stress and electric displacement intensity factors of the crack,as well as the force on dislocation.The derivation is based on the conformal mapping method and the perturbation technique.The influences of the wedge angle and dislocation location on the image force are also discussed.The results obtained in this paper can be fully reduced to some special cases already available or deriving new ones.

Atomistic Simulations of the Effect of Helium on the Dissociation of Screw Dislocations in Nickel

The interactions of He with dissociated screw dislocations in face-centered-cubic （fcc） Ni are investigated by using molecular dynamics simulations based on an embedded-atom method model. The binding and formation energies of interstitial He in and near Shockley partial cores are calculated. The results show that interstitial He atoms at tetrahedral sites in the perfect fee lattice and atoms occupying sites one plane above or below one of the two Shockley partial cores exhibit the strongest binding energy. The attractive or repulsive nature of the interaction between interstitial He and the screw dislocation depends on the relative position of He to these strong binding sites. In addition, the effect of He on the dissociation of screw dislocations are investigated. It is found that Fie atoms homogeneously distributed in the glide plane can reduce the stacking fault width.