Technique for the Measurement of Surgical Screw Deflection

2011 ◽  
Author(s):  
Brendan A. Andrade ◽  
Anil Saigal ◽  
Thomas P. James
Keyword(s):  
Analytical Model ◽  
Bone Substitute ◽  
Bending Moment ◽  
Predictive Ability ◽  
Screw Head ◽  
Mechanics Model ◽  
Synthetic Bone Substitute ◽  
Cortical Screw ◽  
Cyclical Loading ◽  
Bending Loads

Cyclical loading of surgical plating constructs can lead to screw failure through bending loads. In this research, an analytical beam mechanics model was developed to describe the elastic deflection of a cortical screw under a statically applied load. To test the predictive ability of the analytical model, a synthetic bone substitute was used for experiments. The bone substitute was a composite sandwich, consisting of two 6 mm cortical walls separated by a cancellous region. A novel instrument was developed to measure the bending deflection of screws under a radial load applied by a surgical plate at the screw head. A dial indicator and dowel pin arrangement was utilized to measure screw deflection at the screw head and along the length of the screw in order to determine a deflection curve for the screw axis. The analytical model accurately predicted deflection of the screw head at the location of the applied force, but overestimated deflection of the screw body in the cancellous region of the composite bone. Analytical predictions of location of the maximum bending moment matched the location of observed screw fracture in a clinical setting.

Modeling Bicortical Screws Under a Cantilever Bending Load

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Thomas P. James ◽  
Brendan A. Andrade
Keyword(s):  
Cortical Bone ◽  
Elastic Foundation ◽  
Analytical Model ◽  
Bending Moment ◽  
Predictive Ability ◽  
Analytical Models ◽  
Synthetic Bone Substitute ◽  
Bending Load ◽  
Foundation Model ◽  
Cantilever Bending

Cyclic loading of surgical plating constructs can precipitate bone screw failure. As the frictional contact between the plate and the bone is lost, cantilever bending loads are transferred from the plate to the head of the screw, which over time causes fatigue fracture from cyclic bending. In this research, analytical models using beam mechanics theory were developed to describe the elastic deflection of a bicortical screw under a statically applied load. Four analytical models were developed to simulate the various restraint conditions applicable to bicortical support of the screw. In three of the models, the cortical bone near the tip of the screw was simulated by classical beam constraints (1) simply supported, (2) cantilever, and (3) split distributed load. In the final analytical model, the cortices were treated as an elastic foundation, whereby the response of the constraint was proportional to screw deflection. To test the predictive ability of the new analytical models, 3.5 mm cortical bone screws were tested in a synthetic bone substitute. A novel instrument was developed to measure the bending deflection of screws under radial loads (225 N, 445 N, and 670 N) applied by a surrogate surgical plate at the head of the screw. Of the four cases considered, the analytical model utilizing an elastic foundation most accurately predicted deflection at the screw head, with an average difference of 19% between the measured and predicted results. Determination of the bending moments from the elastic foundation model revealed that a maximum moment of 2.3 N m occurred near the middle of the cortical wall closest to the plate. The location of the maximum bending moment along the screw axis was consistent with the fracture location commonly observed in clinical practice.

A novel model of Z-pin insertion in prepreg based on fracture mechanics

2021 ◽  
pp. 095440542110144
Author(s):  
Guobiao Ji ◽  
Liang Cheng ◽  
Shaohua Fei ◽  
Jiangxiong Li ◽  
Yinglin Ke
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Analytical Model ◽  
Model Parameters ◽  
Force Model ◽  
Fe Model ◽  
Cohesive Elements ◽  
Fe Method ◽  
Insertion Force ◽  
Mechanics Model

Through-thickness reinforcement is a promising solution to the problem of delamination susceptibility in laminated composites. Modeling Z-pin–prepreg interaction is essential for accurate robotics-assisted Z-pin insertion. In this paper, a novel Z-pin insertion force model combining the classical cohesive finite element (FE) method with a dynamic analytical fracture mechanics model is proposed. The velocity-dependent cohesive elements, in which the fracture toughness is provided by the analytical model, are implemented in Z-pin insertion FE model to predict the crack initiation and propagation. Then Z-pin insertion experiments are performed on prepreg sample with metallic Z-pins at different velocities to identify the analytical model parameters and validate the simulation predictions offered by the model. Dynamics of Z-pin interaction with inhomogeneous prepreg is described and the effects of insertion velocity on prepreg contact force are studied. Results show that the force model agrees well with experiments and the fracture toughness rises with the increasing Z-pin insertion velocity.

scholarly journals Regeneration of critical-sized defects, in a goat model, using a dextrin-based hydrogel associated with granular synthetic bone substitute

2020 ◽  
Author(s):  
Isabel Pereira ◽  
José Eduardo Pereira ◽  
Luís Maltez ◽  
Alexandra Rodrigues ◽  
Catarina Rodrigues ◽  
...  
Keyword(s):  
Bone Regeneration ◽  
Bone Substitute ◽  
Bone Substitutes ◽  
Multipotent Mesenchymal Stromal Cells ◽  
Micro Computed Tomography ◽  
Synthetic Bone Substitute ◽  
In Situ Forming ◽  
Bioactive Agents ◽  
In Situ Forming Hydrogels

Abstract The development of injectable bone substitutes (IBS) have obtained great importance in the bone regeneration field, as a strategy to reach hardly accessible defects using minimally invasive techniques and able to fit to irregular topographies. In this scenario, the association of injectable hydrogels and bone graft granules is emerging as a well-established trend. Particularly, in situ forming hydrogels have arisen as a new IBS generation. An in situ forming and injectable dextrin-based hydrogel (HG) was developed, aiming to act as a carrier of granular bone substitutes and bioactive agents. In this work, the HG was associated to a granular bone substitute (Bonelike®) and implanted in goat critical-sized calvarial defects (14 mm) for 3, 6 and 12 weeks. The results showed that HG improved the handling properties of the Bonelike® granules and did not affect its osteoconductive features, neither impairing the bone regeneration process. Human multipotent mesenchymal stromal cells from the umbilical cord, extracellular matrix hydrolysates and the pro-angiogenic peptide LLKKK18 were also combined with the IBS. These bioactive agents did not enhance the new bone formation significantly under the conditions tested, according to micro-computed tomography and histological analysis.

SHAFT LOADS ON AZIMUTH PROPULSORS IN OBLIQUE FLOW AND WAVES

2021 ◽  
Vol 153 (A1) ◽  
Author(s):  
H Amini ◽  
S Steen
Keyword(s):  
Mechanical Design ◽  
Bending Moment ◽  
Ship Hull ◽  
Propeller Shaft ◽  
Towing Tank ◽  
Oblique Flow ◽  
Straight Line ◽  
Calm Water ◽  
Bending Loads ◽  
Marine Technology

A range of model experiments have been carried out in calm water and waves for an oil spill vessel model with twin tractor azimuth thrusters at different heading angles and advance coefficients in the large towing tank at the Marine Technology Centre in Trondheim, Norway. Propeller shaft bending loads have been measured using a shaft dynamometer capable of measuring all shaft side force and bending moment components as well as propeller torque and thrust. The results include the loads on the propeller shaft with and without the presence of a ship hull model at the same heading angles and advance velocities in order to study the wake influence from the ship hull on the hydrodynamic loads. Results show that the ship hull wake has a much stronger effect on the propeller loads when the propeller is azimuthed outward from the ship hull centreline than inward. Measurements from the experiments in waves are also presented for the same thruster model in a straight-line course for both the head and following sea states under different wave conditions. Larger bending loads are found in head sea conditions compared with the following sea conditions. Generally it is found that the shaft bending loads and lateral forces are quite large, which is important to consider in the mechanical design layout and for dimensioning of components.

Analytical and Numerical Prediction of Springback of SS/Al-Alloy Cladded Sheet in V-Bending

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Pankaj Kumar Sharma ◽  
Vijay Gautam ◽  
Atul Kumar Agrawal
Keyword(s):  
Analytical Model ◽  
Outer Layer ◽  
Numerical Models ◽  
Yield Criterion ◽  
Bending Moment ◽  
Analytical Models ◽  
Bend Angle ◽  
Radius Of Curvature ◽  
Al Alloy ◽  
First Case

Abstract The present work deals with the development of an analytical model incorporating the effects of anisotropy and strain hardening to predict the springback in V-bending of two-ply sheet metal using a punch profile radius of 15 mm and included a bend angle of 90 deg. In the analytical model, the total bending moment is determined from resulting bending stresses for two different layers arranged in parallel planes one above the other and a new radius of curvature after springback is determined by applying a negative bending moment. The two-ply sheet composed of layers of AA1050 and SS430 is characterized for its tensile properties to be used in analytical and numerical models for prediction of springback. To study the effect of each layer during bending operation, two possible cases of sheet placements during bending and springback are studied; i.e., in the first case, the inner layer is of AA1050 while the SS430 layer is the outer layer whereas in the second case it is opposite. In all the cases of springback experiments when the outer layer is of SS430, the springback values are higher than the values obtained with the specimens when the inner layer is of SS430. This could be attributed to the higher tensile strength of the stainless steel layer and the higher bending radius experienced by it. The springback behaviors are also analyzed by simulations using Hill's anisotropic yield criterion in abaqus software. The springback results obtained by simulations and analytical models are in good agreement in general; however, in some cases, discrepancy of more than 15% is observed in the analytical results when compared with the experimental results.

Is Synthetic Composite Bone a Substitute for Natural Bone in Screw Bending Tests?

2011 ◽  
Author(s):  
Thomas P. James ◽  
Brendan A. Andrade
Keyword(s):  
Bone Substitute ◽  
Bending Strength ◽  
Laminated Composite ◽  
Bovine Bone ◽  
Localized Deformation ◽  
Bending Tests ◽  
Natural Bone ◽  
Cortical Screw ◽  
Glass Fiber Reinforced ◽  
Composite Bone

Composite replica bones have been used extensively for biomechanical studies. These studies normally rely upon the overall tensile, compressive, and bending strength of large replica bones, such as the tibia and femur. In this study, highly localized behavior of composite bone was scrutinized by examining the material’s response to cortical screws in bending. Of interest was localized deformation of the composite material as compared to the response of natural bone under similar loading conditions. Cortical screw deflection in a laminated composite bone was compared to deflection in a bovine bone under quasi-static loading. The laminated composite bone consisted of short glass fiber reinforced epoxy as a cortical bone substitute, while polyurethane foam was used as a cancellous bone substitute. A new laser projection method was used to make comparative measurements of the slope of the screw head near to the applied load. Initial results indicate that composite bone is a reliable substitute for natural bone in quasi-static studies of cortical screw deflection.

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