Effect of Geometry Variation on the Mechanical Behavior of the Proximal Femur (original) (raw)
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Computer Methods and Programs in Biomedicine, 2011
Two dimensional finite element models of cadaveric femoral stiffness were developed to study their suitability as surrogates of bone stiffness and strength, using two dimensional representations of femoral geometry and bone mineral density distributions. If successfully validated, such methods could be clinically applied to estimate patient bone stiffness and strength using simpler and less costly radiographs. Two dimensional femur images were derived by projection of quantitative computed tomography scans of 22 human cadaveric femurs. The same femurs were fractured in a fall on the hip configuration. Femoral stiffness and fracture load were measured, and high speed video was recorded. Digital image correlation analysis was used to calculate the strain distribution from the high speed video recordings. Two-dimensional projection images were segmented and meshed with second-order triangular elements for finite element analysis. Elastic moduli of the finite elements were calculated based on the projected mineral density values inside the elements. The mapping of projection density values to elastic modulus was obtained using optimal parameter identification in a set of nine of the 22 specimens, and validated on the remaining 13 specimens. Finite element calculated proximal stiffness and strength correlated much better with experimental data than areal bone mineral density alone. In addition, finite element calculated strain distributions compared very well with strains obtained from digital image processing of the high speed video recordings, further validating the two-dimensional projected subject-specific finite element models.
Compression or tension? The stress distribution in the proximal femur
2006
Background: Questions regarding the distribution of stress in the proximal human femur have never been adequately resolved. Traditionally, by considering the femur in isolation, it has been believed that the effect of body weight on the projecting neck and head places the superior aspect of the neck in tension. A minority view has proposed that this region is in compression because of muscular forces pulling the femur into the pelvis. Little has been done to study stress distributions in the proximal femur. We hypothesise that under physiological loading the majority of the proximal femur is in compression and that the internal trabecular structure functions as an arch, transferring compressive stresses to the femoral shaft.
A minimal parametric model of the femur to describe axial elastic strain in response to loads
Medical Engineering & Physics, 1996
Evaluating the state of stress/strain for a given geometry and load in femurs can be done both experimentally, measuring strain at a limited number of locations, and theoretically with finite ekment models. Another approach is to describe the state of strain with a fm synthetic indices. For this purpose the reverse elastic problem (i.e. bone parameters are estimated given the strain d&ibution and loads) needs to be solved as opposed to the finite element direct problem.
Computer Methods in Biomechanics and Biomedical Engineering, 2012
Skeletal fractures associated with bone mass loss are a major clinical problem and economic burden, and lead to significant morbidity and mortality in the aging population. Clinical image based measures of bone mass show only moderate correlative strength with bone strength. However, engineering models derived from clinical image data predict bone strength with significantly greater accuracy. Currently, image-based finite element (FE) models are time consuming to construct and are non parametric. The goal of this study was to develop a parametric proximal femur FE model based on a statistical shape and density model (SSDM) derived from clinical image data. A small number of independent SSDM parameters described the shape and bone density distribution of a set of cadaver femurs and captured the variability affecting proximal femur FE strength predictions. Finally, a 3D FE model of an "unknown" femur was reconstructed from the SSDM with an average spatial error of 0.016 mm and an average bone density error of 0.037 g/cm 3 .
IJERT-Computational Modeling of Human Femur using CT Data for Finite Element Analysis
International Journal of Engineering Research and Technology (IJERT), 2014
https://www.ijert.org/computational-modeling-of-human-femur-using-ct-data-for-finite-element-analysis https://www.ijert.org/research/computational-modeling-of-human-femur-using-ct-data-for-finite-element-analysis-IJERTV1IS6040.pdf Three-dimensional finite element modeling is widely used to generate reliable subject-specific FE model using Computed Tomography (CT) data that accurately predicts information about bone morphology and tissue density. CT scan data is widely used to make realistic investigations on the mechanical behavior of bone structures using Finite Element Analysis (FEA). The purpose of this paper is to create 3-D finite element models of the right human proximal femur for three male patients of 17 yrs, 32 yrs and 40 yrs using CT scan data for FEA loaded by individual body weight of 75 Kg, 72 Kg and 66 Kg respectively which is shared equally by the lower limbs, at different inclination angles and to determine the total deformation, equivalent Von Mises stress, maximum principal stress, fatigue tool and percentage variation. Analysis of these models will provide data unavailable at this time to orthopaedic surgeons, engineers and researchers of human orthopaedics.
Annals of biomedical engineering, 2015
Statistical models were developed that predict male and female femur geometry as functions of age, body mass index (BMI), and femur length as part of an effort to develop lower-extremity finite element models with geometries that are parametric with subject characteristics. The process for developing these models involved extracting femur geometry from clinical CT scans of 62 men and 36 women, fitting a template finite element femur mesh to the surface geometry of each patient, and then programmatically determining thickness at each nodal location. Principal component analysis was then performed on the thickness and geometry nodal coordinates, and linear regression models were developed to predict principal component scores as functions of age, BMI, and femur length. The average absolute errors in male and female external surface geometry model predictions were 4.57 and 4.23 mm, and the average absolute errors in male and female thickness model predictions were 1.67 and 1.74 mm. The...
Evaluación del campo de estrés combinado de flexión y compresión en un fémur proximal humano
Revista mexicana de ingeniería biomédica, 2003
One of the topics that has attracted attention is the exact evaluation of the mechanical behavior of the human femur. Several studies have been done, in order to establish if the femur is under compression or bending. For this purpose, experimental stress analysis has been applied, common techniques such as reflection photoelasticity or strain gages have been used. In the first case, the complete
Development, validation, and application of a parametric finite element femur model
2014
Older, obese, and female occupants have higher risk of serious lower-extremity injuries in frontal crashes. Optimizing vehicle restraints to better protect of these vulnerable populations, requires finite element (FE) models of the human body that consider the variations in skeletal geometry, body size, body shape, posture, and material properties among the population. This paper describes the development, validation, and application of a parametric femur FE model as an example of these methods for an entire lower-extremity FE model. Bone geometries were extracted from CT scans from 98 subjects. A landmark-based mesh morphing and projecting process was used to fit a template mesh to the femur geometry from each subject. Thicknesses of cortical bone at each node of the template mesh were programmatically determined. The nodal coordinates and the cortical bone thicknesses of the fitted meshes were analyzed using principal component analysis and regression analysis to develop a statistical model of the femur that predicts femur nodal coordinate locations representing the bone surface geometry as well as the associated cortical thickness as functions of age, BMI, and femur length. The parametric FE model was validated by running 13 subject-specific simulations and comparing measured results from a study of femur PMHS tests in combined 3-point bending and compression loading conditions to predicted results. The validated FE model was then used to investigate the effects of occupant characteristics on femur response values. The statistical model showed good fit to PMHS femur geometries, and the FE model was able to match the subject-specific test results. The average error in the force curve results for the combined loading tests was about 1%. In the initial application loading condition, an increase in BMI caused an increase in peak force, while an increase in age caused a small decrease in peak force.
Accuracy of finite element predictions in sideways load configurations for the proximal human femur
Journal of Biomechanics
Subject-specific finite element models have been used to predict stress-state and fracture risk in individual patients. While many studies analysed quasi-axial loading configurations, only few works simulated sideways load configurations, such as those arising in a fall. The majority among these latter directly predicted bone strength, without assessing elastic strain prediction accuracy. The aim of the present work was to evaluate if a subject-specific finite element modelling technique from CT data that accurately predicted strains in quasi-axial loading configurations is suitable to accurately predict strains also when applying low magnitude loads in sideways configurations. To this aim, a combined numerical-experimental study was performed to compare finite element predicted strains with straingauge measurements from three cadaver proximal femurs instrumented with sixteen strain rosettes and tested non-destructively under twelve loading configurations, spanning a wide cone (0-301 for both adduction and internal rotation angles) of sideways fall scenarios. The results of the present study evidenced a satisfactory agreement between experimentally measured and predicted strains (R 2 greater than 0.9, RMSE% lower than 10%) and displacements. The achieved strain prediction accuracy is comparable to those obtained in state of the art studies in quasi-axial loading configurations. Still, the presence of the highest strain prediction errors (around 30%) in the lateral neck aspect would deserve attention in future studies targeting bone failure.
Journal of Biomechanics, 2011
Proximal femur Femoral neck and head Linear elastic behavior In vitro bone fracture Brittle failure a b s t r a c t It has not been demonstrated whether the human proximal femur behaves linearly elastic when loaded to failure. In the present study we tested to failure 12 cadaveric femurs. Strain was measured (at 5000 Hz) on the bone surface with triaxial strain gages (up to 18 on each femur). High-speed videos (up to 18,000 frames/s) were taken during the destructive test. To assess the effect of tissue preservation, both fresh-frozen and formalin-fixed specimens were tested. Tests were carried out at two strain-rates covering the physiological range experienced during daily motor tasks. All specimens were broken in only two pieces, with a single fracture surface. The high-speed videos showed that failure occurred as a single abrupt event in less than 0.25 ms. In all specimens, fracture started on the lateral side of the neck (tensile stress). The fractured specimens did not show any sign of permanent deformation. The forcedisplacement curves were highly linear (R 2 40.98) up to 99% of the fracture force. When the last 1% of the force-displacement curve was included, linearity slightly decreased (minimum R 2 ¼ 0.96). Similarly, all force-strain curves were highly linear (R 2 4 0.98 up to 99% of the fracture force). The slope of the first part of the force-displacement curve (up to 70% fracture force) differed from the last part of the curve (from 70% to 100% of the fracture force) by less than 17%. Such a difference was comparable to the fluctuations observed between different parts of the curve. Therefore, it can be concluded that the proximal femur has a linear-elastic behavior up to fracture, for physiological strain-rates.