Wedge Displacement Research Articles

Preservation of the posterolateral cortex may not affect the biomechanical stability of lateral intra-articular varus osteotomy of the proximal tibia

BackgroundLateral intra-articular varus osteotomy is an L-shaped osteotomy of the lateral tibial condyle to correct mild knee valgus and lateral plateau malunion of the proximal tibia. In order to minimize injury, it was modified to preserve the posterolateral cortex and the upper tibiofibular joint. The aim of this study was to evaluate the stability of modified lateral intra-articular varus osteotomy by comparing the biomechanical strength with lateral intra-articular varus osteotomy. MethodsTwenty-four synthetic tibia models were divided into 2 groups based on osteotomy type. Each model was then fixed with 2 commonly used plate systems. Biomechanical tests were conducted to measure parameters including construct stiffness, wedge displacement, and the number of failed specimens, and the results were compared among different groups. FindingsNo significant difference was found in construct stiffness among all groups (P > 0.05). There was also no significant difference in wedge displacement among all groups (P > 0.05). When an axial load of 1500 N was applied, the number of failed specimens showed no significant difference among all groups (P > 0.05). The main failure pattern was additional fracture lines on the lateral tibial plateau. InterpretationThe findings indicate that there was no significant difference in stability between the 2 groups under the tested loading conditions. Furthermore, it appears that preserving the posterolateral cortex may have no impact on biomechanical stability.

Biomechanical evaluation of different types of lateral hinge fractures in medial opening wedge high tibial osteotomy

BackgroundLateral hinge fractures are common complications in the medial opening wedge high tibial osteotomy for treatment of knee osteoarthritis. The rehabilitation protocols are decided depending on the remaining stability following these fractures. This study aimed to evaluate the biomechanical properties of different types of lateral hinge fractures in medial opening wedge high tibial osteotomy. MethodsTwenty synthetic tibia models were used as test samples. A 10-mm bone wedge was removed from the medial side of the proximal tibias to create the bone defect. The samples were then divided into 4 groups: (1) intact lateral hinge; (2) Takeuchi type I fractures; (3) type II fractures; and (4) type III fractures. After fixation with a locking plate, the stability parameters including construct stiffness, wedge displacement, and construct strength were tested under compressive forces and compared among the 4 groups. FindingsNo statistical difference was found in the construct stiffness among the 4 groups (P = 0.78). The type III fractures had the largest wedge displacement compared with the other 3 groups. The failure loads on average were significantly reduced in the type III fractures compared with those with intact hinge (P < 0.01) and in type I fractures (P = 0.04). No statistical difference was observed between the type I fractures and the intact hinge in terms of wedge displacement or failure loads. InterpretationThe type III fractures were the most unstable and patients with these fractures should be managed cautiously. Delayed weightbearing and/or additional fixation should be considered.

Combined proximal tibial osteotomy for varus osteoarthritis of the knee: Biomechanical tests and finite-element analyses

BackgroundA special combined proximal tibial osteotomy (CPTO) was designed to correct varus osteoarthritis of the knee with severe intra-articular pathologies, which could not be fully corrected by opening-wedge high tibial osteotomy (OWHTO). The biomechanical strength of the CPTO bone–implant construct was evaluated and compared with those of existing osteotomy methods. MethodsThree variations of osteotomy including OWHTO, tibial condylar valgus osteotomy (TCVO), and CPTO were performed on synthetic bones with locking plate and screws. Wedge stiffness, wedge displacement, and load failure were measured by biomechanical tests. Three types of numerical tibial models were also constructed by three-dimensional model reconstruction software. The stability parameters of the three variations including wedge stiffness, wedge displacement, and stress distribution were further measured by finite-element analyses. ResultsThe biomechanical testing results revealed that the wedge stiffness, wedge displacement, and failure load of the CPTO construct were very close to those of the OWHTO construct. The numerical results of wedge stiffness and displacement showed good conformity to the previous biomechanical results. The stress distribution at the lateral hinge, the plate corner, and the holes of the CPTO construct were close to those of the OWHTO counterpart, while the stress distribution at the inter-condylar eminence of the tibia and at the middle region of the screws was close to those of the TCVO counterpart. ConclusionsThe CPTO construct can provide comparable strength for early mobilization and rehabilitation to that of the OWHTO construct.

Characterisation of the tensile constitutive behaviour of fibre-reinforced concrete: A new configuration for the Wedge Splitting Test

The fib Model Code chose the EN14651 test as the basic method for evaluating the structural behaviour of fibre-reinforced concrete (FRC). However, there are technological restrictions that must be considered. For example, this test has a relatively complex execution, and it is difficult to carry it out under samples extracted from real structures. In this study, an experimental campaign is developed to validate a new test, called Montevideo (MVD) test, for FRC. The test is based on the wedge-splitting test, but simplifications in terms of sample preparation and loading device allow it to be used in routine quality control. The results show a) a stable friction coefficient between the wedge and sample; b) a linear relationship between wedge displacement and crack mouth opening displacement (CMOD), which allows conducting the test through the stroke displacement only; c) a coefficient of variation below the usual range of the EN14651 test; and d) a load correlation factor (kMVD = 2.5) to transform the loads from the MVD test to EN14651 test for large values of CMODs (above 2 mm). This test can be performed on samples prepared from extracted cores with an open displacement control system in specimens with softening behaviour, and without producing post-peak instabilities. The development of the MVD test provides a practical and simple method for controlling the FRC quality, complementary to the EN14651 test.

Laboratory investigation of water extraction effects on saltwater wedge displacement

There is a close connection between saltwater intrusion into aquifers and groundwater extraction. Freshwater extraction in coastal aquifers is one of the most important reasons for the saltwater intrusion into these aquifers. Condition of extraction system such as well depth, discharge rate, saltwater concentration and etc. could affect this process widely. Thus, investigating different extraction conditions comprises many management advantages. In the present study, the effects of freshwater extraction on saltwater interface displacement have been investigated in a laboratory box. Three different well depths (H) were considered with combinations of 3 different extraction rates (Q) and 3 saltwater concentrations (C) for detailed investigation of the effects of these factors variations on saltwater displacement. SEAWAT model has been used to simulate all the scenarios to numerically study of the process. The experimental and numerical results showed that when the C and Q rates were small and the well depth was shallow, the saltwater interface wouldn’t reach the extraction well, so the extracted water remained uncontaminated. When the C and Q rates were increased and the well was deepened, the salinity of the extracted water became higher. When the Q and C rates were high enough, in the shallow well depth, the final concentration of the extracted water was low but a huge part of the porous media was contaminated by the saltwater, furthermore when the well was deepened enough, the final concentration of the extracted water was increased but a small part of the porous media was contaminated by the saltwater. Finally, the results showed that when the Q and H rates were high enough, the extraction well behaved like a barrier and didn’t allow the advancing saltwater wedge toe to be intruded beyond the wells.

Comminuted supracondylar femoral fractures: a biomechanical analysis comparing the stability of medial versus lateral plating in axial loading.

The aim of this study was to compare the biomechanical properties of medial and lateral plating of a medially comminuted supracondylar femoral fracture. A supracondylar femoral fracture model comparing two fixation methods was tested cyclically in axial loading. One-centimetre supracondylar gap osteotomies were created in six synthetic femurs approximately 6 cm proximal to the knee joint. There were two constructs investigated: group 1 and group 2 were stabilized with an 8-hole LC-DCP, medially and laterally, respectively. Both construct groups were axially loaded. Global displacement (total length), wedge displacement, bending moment and strain were measured. Medial plating showed a significantly decreased displacement, bending moment and strain at the fracture site in axial loading. Medial plating of a comminuted supracondylar femur fracture is more stable than lateral plating.

A Comparative Study of Rock Wedge Stability of an Arch Dam Abutment Subjected to Static and Seismic Loading

In the present paper, the stability evaluation of a rock wedge in an arch dam abutment under static and seismic loading is studied via the finite element (FE) method and a conventional method. The Luzzone arch dam in Switzerland is selected as a case study in which response of the potential wedge at the left abutment is investigated. In the FE models, the reservoir's water is assumed compressible and the coupled system is solved simultaneously. Also, the foundation is studied for two different cases; massless and massed medium via viscous boundary on the far-end truncated boundary. In addition, the effect of modeling joint between the wedge and the remaining foundation medium on the wedge displacements is considered. The results of the FE models are compared with those obtained from the traditional method in which wedge stability is evaluated utilizing the Londe method. The results reveal that the traditional method overestimates the wedge displacement in comparison with the finite element technique.

Major complications and risk factors associated with surgical correction of congenital medial patellar luxation in 124 dogs.

Dogs treated for congenital medial patellar luxation were reviewed for the purpose of determining the incidence of postoperative major complications requiring surgical revision and the risk factors for their occurrence. Major complications occurred in 18.5% of the patellar luxation stabilization procedures with implant associated complications being the most frequent, patellar reluxation the second, and tibial tuberosity avulsion the third most common major complication. Other complications included patellar ligament rupture and trochlear wedge displacement. When recession trochleoplasty was performed in addition to tibial tuberosity transposition, a 5.1-fold reduction in the rate of patellar reluxation was observed. Release of the cranial belly of the sartorius muscle further reduced the incidence of patellar reluxation, while patella alta (pre- or postoperative) and patellar luxation grade were not found to influence the rate of reluxation. Tibial tuberosity avulsion was 11.1-times more likely when using a single Kirschner wire to stabilize a transposition, compared with two Kirschner wires. Independent to the number of Kirschner wires used, the more caudodistally the Kirschner wires were directed, the higher the risk for tibial tuberosity avulsion. Tension bands were used in 24.4% of the transpositions with no tuberosity avulsion occurring in stifles stabilized with a tension band. Overall, grade 1 luxations had a significantly lower incidence of major complications than other grades, while body weight, age, sex, and bilateral patellar stabilization were not associated with risk of major complication development.

Multi-parameter crack tip stress state description for estimation of fracture process zone extent in silicate composite WST specimens

For wedge splitting test specimens, the stress and displacement fields both in the vicinity and also in larger distance from the crack tip are investigated by means of numerical methods. Several variants of boundary conditions were modeled. The stress intensity factor K, T-stress and even higher-order terms of William series were determined and subsequently utilized for analytical approximation of the stress field. A good fit between the analytical and numerical solution in dependence on the distance from the crack tip was shown, compared and discussed. Presented approach is considered as suitable for estimation of the fracture process zone extent in silicate composite materials.

Novel particle method for modelling the episodic collapse of soft coastal bluffs

This paper presents a new, novel, particle-based Bluff Morphology Model (BMM), and with it investigates the stability, collapse, and equilibrium position of soft coastal bluffs (cliffs). This model combines a multiple wedge displacement method with an adapted Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method. At first, the wedge method is applied to compute the stability of the bluff. Once the critical failure mechanism of the bluff slope has been identified, and if the factor of safety for the mechanism is less than 1, the adapted WCSPH method is used to predict the failure movement and residual shape of the slope. The model is validated against benchmark test cases of bluff stability for purely frictional, purely cohesive, and mixed strength bluff materials including 2D static water tables. The model predictions give a good correlation with the expected values, with medium resolution models producing errors of typically less than 2.0%. In addition, the prediction of lateral movement of a surveyed cliff and the dynamic collapse of a vertical bluff are computed, and compare well with published literature.

Semiempirical Model for Initial Displacement of Salt Water Wedge in a Bar-Blocked Estuary

The interaction of continuous freshwater flow from an upstream basin into a bar-blocked estuary is investigated following ideas previously proposed by Debler and Imberger. The interface point, defined as the point of confluence between the initial saltwater wedge and the freshwater, is considered to be characteristic of the interaction between the water bodies. The previous semiempirical model of Coates and Guo has been reconsidered on the basis of realistic wedge shapes obtained from physical and numerical experiments. The approach considers conservation and conversion of energies in the dynamic environment. The present approach enabled the writers to obtain a semiempirical model that matches published experimental data fit for the initial phase of the wedge displacement. It is observed that the new model complements the earlier relationship of Coates and Guo for predicting the salt wedge dynamics for the initial phase of the interaction.

Modeling Cutting: Plastic Deformation of Polymer Samples Indented With a Wedge

An experiment was designed to relate force to plastic deformation caused by a wedge indenting the edge surface of a polymer sample. The experiment reveals the primary phenomena observed in industrial converting processes of cutting and slitting of thin polymer films. The thin film was modeled using a polycarbonate rectangular block, which was indented with a metallic half-round wedge that represents the industrial cutter blades. The wedge radius and sample size were selected to scale to the ratio of slitting blade radius and industrial film thickness. A compression test frame impressed wedges into polymer samples with measurements of both force and displacement recorded. These experiments clearly revealed the shape of the plastic deformation zone ahead of and around the wedges. Data from the experiments showed increasing cutting force with wedge displacement until the sample fractured. Plastic deformation of the samples was examined: the out-of-plane plastic volume was shown to equal the volume displaced by the wedge. Cracks that developed from the side of the wedge tip during indention propagated with near steady-state loads under edge surface indention.

A generalized solution for tetrahedral rock wedge stability analysis

It has been found that the limit equilibrium approach commonly used for tetrahedral rock wedge stability analysis is statically indeterminate and the conventional method proposed in textbooks actually involves an assumption that the shear forces applied on the failure planes are parallel to the line of intersection. A new method that allows an input of various shear force directions is presented in this paper. This method starts from an assumed wedge displacement vector that can be related to the shear force directions. By applying the limit equilibrium conditions a governing equation calculating the factor of safety has been obtained. This equation also permits a formal demonstration to confirm that a maximum factor of safety exists when the rock wedge dilates at values of friction angles to the left and right failure planes respectively, the direction required Mohr–Coulomb's associative flow law. The generalized method therefore provides a theoretical support to some fundamental postulates in Plasticity. The factors of safety obtained by the conventional method and the generalized approach are not substantially different if the shear strength of the failure planes involves a reasonable value of cohesion. However the deviations between the two approaches can be remarkable if the material is purely frictional. Further study by physical model testing and field investigation is recommended.

Limit equilibrium approach to study the evolution of shear band systems in soils

The paper is concerned with the analysis of shear band systems appearing in dry soil behind flexible retaining walls under plane strain conditions. The experimental problem studied is that of an initially vertical, plane retaining wall, deforming because of the gradual excavation of sand from one side of the wall. The aim of the paper is to clarify some of the possible physical reasons for multiple shear bands developing behind such walls. The problem of shear band arrangement in a regular pattern, and their possible sequence, are also considered. The behaviour of soil adjacent to the wall is modelled by a set of rigid blocks, cut off from the soil body by lines parallel to the classical Coulomb wedge ‘slip line’ and sliding subsequently on each other. The distance between subsequent shear bands is calculated from the equilibrium of an actual soil wedge, which may contain previously activated wedges. An elastic behaviour of the wall is taken into account in a simplified way when equilibrium is verified. The plastic softening of soil is expressed in terms of the angle of internal friction or cohesion decreasing linearly with soil wedge displacement. The present simplified analysis is aimed as an explanation of shear band patterns, and constitutes a first step towards more refined treatments.

Finite element modelling of recirculating density-driven saltwater intrusion processes in groundwater

This paper is concerned with an appropriate finite element model for solving transient and steady-state density-driven saltwater intrusion processes in groundwater with or without free surface. Alternative formulations and several numerical solution strategies are discussed. A comparative study is given for a cellular benchmark problem. An implicit predictor-corrector method with automatically adjusted time stepping involving a full Newton method is studied. Results on saltwater wedge displacement and gravity-driven sinking of saltwater from a deposit into the subsurface illustrate the efficacy of the model chosen. The results for the saltwater wedge problems are compared with analytical sharp-interface assessments.

A random-walk model for helix bending in B-DNA.

The double-helical B-DNA dodecamer of sequence d(C-G-C-G-A-A-T-T-C-G-C-G) has been refined independently from x-ray crystal structure analyses in five different variants: d(C-G-C-G-A-A-T-T-C-G-C-G) at 16 K, at room temperature, and with bound cis-diamminedichloroplatinum(II), and d(C-G-C-G-A-A-T-T-brC-G-C-G) in 60% 2-methyl-2,4-pentanediol at 20 degrees C and 7 degrees C. These helices display overall axial bends of 22 degrees, 18 degrees, 17 degrees, 14 degrees, and 3 degrees, respectively, providing an opportunity to investigate the nature of the bending process in B-DNA. Bending from one base pair to the next is best described as a stochastic or random-walk process, having forward, retrograde, and sidewise individual steps, but with an overall sense of bending. Individual steps almost always involve rolling of adjacent base pairs over one another along their long axes, not a tilting or wedge displacement that lifts neighboring base pairs apart at one end. A slight preference is observed for bending the double helix in a direction that compresses the major groove rather than the minor, and this is intuitively reasonable in view of the narrowness of the minor groove and its occupation by the spine of hydration that stabilizes the B form of DNA. This model predicts that, when DNA is wound around the nucleosome core, it should not be smoothly curved but should exhibit discrete bends every five base pairs as proposed by Zhurkin et al. [Zhurkin, V.B., Lysov, Y. P. & Ivanov, V. I. (1979) Nucleic Acids Res. 6, 1081-1096)]. Sharper bends may occur at alternate positions, where the major groove faces the nucleosome core.

Forces Under the Hallux Valgus Foot Before and After Surgery

Abnormalities in the hallux valgus foot and changes after surgery were investigated by measuring the distribuiion of load on the foot in walking. Hallux valgus was associated with reduced load imposed on the toes, and on the medial side of the forefoot, compared with a large sample of healthy feet. Abnormalities correlated with the degree of the deformity. Both Keller's operation and a wedge displacement osteotomy of the first metatarsal not only failed to restore normal loading but increased the abnormalities of loading seen preoperatively. A large decrease in the angle between first and second metatarsals as a result of surgery minimized this increase. A silastic arthroplasty did not carry high loads when used to treat hallux valgus, but near normal loads were imposed on it when used for hallux rigidus. Considerable variability was found in the loading distribution on the healthy feet. The distribution between first and second metatarsal heads was partially dependent upon their protrusions, relative to the direction of walking. The changes in the relationships between the loadings on the forefoot and skeletal shape in response to surgical operations are important for our understanding of treatment of the hallux valgus foot.

Enhancing Ultrasonic Bond Development

To enhance ultrasonic bond development, an improved understanding is needed of the processes taking place at the bond interface. This work is designed to determine the role that bonding parameters play in contributing to bond development. Of particular concern are the effects created by the machine variables, i.e., load, power, and time. Silicon was selected as a bond surface for aluminum wire bonds. The brittle nature of silicon provides a permanent record of the bonding history. With both the crystal orientation and defects of the silicon well characterized prior to bonding, features such as the location of residual bonding strains in the silicon were determined. The pattern of partially bonded material exposed by peeling underdeveloped bonds simulates a torus (or doughnut) with an unbonded central region. Features of aluminum wire bonds to aluminum, glass, beryllium, and silicon were compared to show that a common mechanism exists independent of the bond surface material. The ability to bond to silicon varies with wire composition. For example, both Al-0.5% Mg and pure Al wires bond readily, while Al-l% Si wire does not. Two modes of material flow characterize interfacial behavior. Ultrasonic energy promotes a material softening which, in conjunction with the applied load, results in a gross flow to expose fresh material for bonding. In the second stage of material flow, a wave form is propagated through the wire to the periphery of the wire-silicon interface. This wave form is observed as a periodic cutting action into the silicon perpendicular to the pulsing direction. A fine ball-like formation in the grooves of the wave region at the bond zone was a feature common to the different bonding surfaces. The wavelength and wave amplitude vary linearly with the applied power as does the tip-to-tip displacement of the wedge. The groove spacings are of the same magnitude as the wedge displacement. For constant power and time, increased load increases the size of the central bond region that does not experience the wave action. For constant load and power, the width of the wave affected periphery increases toward the center of the bond with time. The method of thermally induced stacking faults by steam oxidation was used to characterize the residual bond strains in the silicon. Faulting was found in the peripheral region of the bond where the wave action was operable. This faulting correlated to stresses generated in the pulsing direction and not to the directions of gross material flow. Reliable bonding depends upon a proper control of the gross and wave flow processes by optimizing material properties as well as machine variables. A model has been developed to qualitatively relate the influence of these variables and the manner in which a change in one parameter affects the response of the remaining variables.