A new approach for assigning bone material properties from CT images into finite element models

The aim of this study was to determine the accuracy of specimen-specific finite element models of untreated and cement-augmented vertebrae by direct comparison with experimental results. Eleven single cadaveric vertebrae were imaged using micro computed tomography (mCT) and tested to failure in axial compression in the laboratory. Four of the specimens were first augmented with PMMA cement to simulate a prophylactic vertebroplasty. Specimen-specific finite element models were then generated using semi-automated methods. An initial set of three untreated models was used to determine the optimum conversion factors from the image data to the bone material properties. Using these factors, the predicted stiffness and strength were determined for the remaining specimens (four untreated, four augmented). The model predictions were compared with the corresponding experimental data. Good agreement was found with the non-augmented specimens in terms of stiffness (root-mean-square (r.m.s.) error 12.9 per cent) and strength (r.m.s. error 14.4 per cent). With the augmented specimens, the models consistently overestimated both stiffness and strength (r.m.s. errors 65 and 68 per cent). The results indicate that this method has the potential to provide accurate predictions of vertebral behaviour prior to augmentation. However, modelling the augmented bone with bulk material properties is inadequate, and more detailed modelling of the cement region is required to capture the bone—cement interactions if the models are to be used to predict the behaviour following vertebroplasty.

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Orientation definition of anisotropy is important to finite element simulation of bone material properties

10.54294/9x1rzs ◽

2008 ◽

Author(s):

Haisheng Yang ◽

Tongtong Guo ◽

Xin Ma

Keyword(s):

Finite Element ◽

Finite Element Simulation ◽

Material Property ◽

Material Properties ◽

Great Influence ◽

Biomechanical Analysis ◽

Von Mises Stress ◽

Bone Material ◽

Bone Material Properties ◽

Element Simulation

The assignment of bone material properties to finite element model is a fundamental step in finite element analysis and has great influence on analysis results. Most work done in this area has adopted isotropic assignment strategy as its simplicity. However, bone material is widely recognized as being anisotropic rather than isotropic. Therefore, this work is aimed to simulate the inhomogeneity and anisotropy of femur by assigning each element of the mesh model the material properties with a numerical integration method and properly defining the principal material orientation, and then compare the biomechanical analysis results of isotropic model with that of anisotropic model under six different loading conditions. Based on the analysis results of the equivalent Von Mises stress and the nodal displacement, four different regions of interest are chosen to achieve this comparison. The results show that significant differences between the two material property assignments exist in the regions where anisotropic material property is sensitive to orientation definition. Thus, orientation definition is important to finite element simulation of bone material properties.

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Bone material properties as measured by Reference Point Indentation are low in subjects with acromegaly

Bone Abstracts ◽

10.1530/boneabs.5.p35 ◽

2016 ◽

Author(s):

Frank Malgo ◽

Neveen A T Hamdy ◽

Alberto M Pereira ◽

Nienke R Biermasz ◽

Natasha M Appelman-Dijkstra

Keyword(s):

Material Properties ◽

Reference Point ◽

Bone Material ◽

Bone Material Properties ◽

Reference Point Indentation

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Developments in Modelling Bone Screwing

Current Directions in Biomedical Engineering ◽

10.1515/cdbme-2020-3029 ◽

2020 ◽

Vol 6 (3) ◽

pp. 111-114

Author(s):

Jack Wilkie ◽

Paul D. Docherty ◽

Knut Möller

Keyword(s):

Material Properties ◽

Frictional Coefficient ◽

Viscous Friction ◽

Model Parameters ◽

General Shape ◽

Bone Material ◽

Bone Material Properties ◽

Modelling Methodology ◽

Recorded Data ◽

Friction Models

AbstractINTRODUCTION: A torque-rotation model of the bone-screwing process has been proposed. Identification of model parameters using recorded data could potentially be used to determine the material properties of bone. These properties can then be used to recommend tightening torques to avoid over or under-tightening of bone screws. This paper improves an existing model to formulate it in terms of material properties and remove some assumptions. METHOD: The modelling methodology considers a critical torque, which is required to overcome friction and advance the screw into the bone. Below this torque the screw may rotate with elastic deformation of the bone tissue, and above this the screw moves relative to the bone, and the speed is governed by a speed-torque model of the operator’s hand. The model is formulated in terms of elastic modulus, ultimite tensile strength, and frictional coefficient of the bone and the geometry of the screw and hole. RESULTS: The model output shows the speed decreasing and torque increasing as the screw advances into the bone, due to increasing resistance. The general shape of the torque and speed follow the input effort. Compared with the existing model, this model removes the assumption of viscous friction, models the increase in friction as the screw advances into the bone, and is directly in terms of the bone material properties. CONCLUSION: The model presented makes significant improvements on the existing model. However it is intended for use in parameter identification, which was not evaluated here. Further simulation and experimental validation is required to establish the accuracy and fitness of this model for identifying bone material properties.

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Constitutive Laws for Biomechanical Modeling of Refractive Surgery

Journal of Biomechanical Engineering ◽

10.1115/1.2796033 ◽

1996 ◽

Vol 118 (4) ◽

pp. 473-481 ◽

Cited By ~ 122

Author(s):

Michael R. Bryant ◽

Peter J. McDonnell

Keyword(s):

Finite Element ◽

Material Properties ◽

Refractive Surgery ◽

Fiber Optic ◽

Transverse Isotropy ◽

Constitutive Laws ◽

Finite Element Models ◽

Corneal Refractive Surgery ◽

Best Fit ◽

Membrane Inflation

Membrane inflation tests were performed on fresh, intact human corneas using a fiber optic displacement probe to measure the apical displacements. Finite element models of each test were used to identify the material properties for four different constitutive laws commonly used to model corneal refractive surgery. Finite element models of radial keratotomy using the different best-fit constitutive laws were then compared. The results suggest that the nonlinearity in the response of the cornea is material rather than geometric, and that material nonlinearity is important for modeling refractive surgery. It was also found that linear transverse isotropy is incapable of representing the anisotropy that has been experimentally measured by others, and that a hyperelastic law is not suitable for modeling the stiffening response of the cornea.

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The Role of Topology and Tissue Mechanics in Remora Attachment

MRS Proceedings ◽

10.1557/opl.2014.229 ◽

2014 ◽

Vol 1648 ◽

Cited By ~ 5

Author(s):

Michael Culler ◽

Keri A. Ledford ◽

Jason H. Nadler

Keyword(s):

Finite Element ◽

Material Properties ◽

Tissue Mechanics ◽

Unit Cell ◽

Surface Topology ◽

Finite Element Models ◽

Cell Geometry ◽

Critical Step ◽

Tissue Material

ABSTRACTRemora fish are capable of fast, reversible and reliable adhesion to a wide variety of both natural and artificial marine hosts through a uniquely evolved dorsal pad. This adhesion is partially attributed to suction, which requires a robust seal between the pad interior and the ambient environment. Understanding the behavior of remora adhesion based on measurable surface parameters and material properties is a critical step when creating artificial, bio-inspired devices. In this work, structural and fluid finite element models (FEM) based on a simplified “unit cell” geometry were developed to predict the behavior of the seal with respect to host/remora surface topology and tissue material properties.

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Modeling the HSK Toolholder-Spindle Interface

Journal of Manufacturing Science and Engineering ◽

10.1115/1.1480023 ◽

2002 ◽

Vol 124 (3) ◽

pp. 734-744 ◽

Cited By ~ 14

Author(s):

Ihab M. Hanna ◽

John S. Agapiou ◽

David A. Stephenson

Keyword(s):

Finite Element ◽

Material Properties ◽

System Reliability ◽

High Volume ◽

Finite Element Models ◽

Operational Experience ◽

Bending Load ◽

Load Carrying ◽

Detailed Evaluation ◽

Contact Pressures

The HSK toolholder-spindle connection was developed to overcome shortcomings of the 7/24 steep-taper interface, especially at higher speeds. However, the HSK system was standardized quickly, without detailed evaluation based on operational experience. Several issues concerning the reliability, maintainability, and safety of the interface have been raised within the international engineering community. This study was undertaken to analytically investigate factors which influence the performance and limitations of the HSK toolholder system. Finite Element Models were created to analyze the effects of varying toolholder and spindle taper geometry, axial spindle taper length, drawbar/clamping load, spindle speed, applied bending load, and applied torsional load on HSK toolholders. Outputs considered include taper-to-taper contact pressures, taper-to-taper clearances, minimum drawbar forces, interface stiffnesses, and stresses in the toolholder. Static deflections at the end of the holder predicted by the models agreed well with measured values. The results showed that the interface stiffness and load-carrying capability are significantly affected by taper mismatch and dimensional variations, and that stresses in the toolholder near the drive slots can be quite high, leading to potential fatigue issues for smaller toolholders subjected to frequent clamping-unclamping cycles (e.g., in high volume applications). The results can be used to specify minimum toolholder material properties for critical applications, as well as drawbar design and spindle/toolholder gaging guidelines to increase system reliability and maintainability.

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