Ovine models are widely used in orthopaedics and trauma research. We present the development and validation of an FE model of an ovine tibia for use in the testing of tibia fracture fixation plates. The FE model was generated from CT data of a cadaveric tibia and validated by mechanical testing of the bone. An offset 3-pt bend test was conducted with strain gauges placed on the anterior and posterior surfaces of the diaphysis. The loads applied during testing were applied to the model after digitising their location and orientation with a 3D digitiser. A comparison of the surface strains was conducted. Initial results show a good correlation between the mechanical test and the FE model with calculated strain values within 2% of the measured strains. Further improvements are expected with the incorporation of bone density-specific material properties in the model

Epari, Devakara R.

Grant, Caroline A.

Schmutz, Beat

Schuetz, Michael

Steck, Roland

Queensland University of Technology ePrints Archive

                   QUT Digital Repository:  http://eprints.qut.edu.au/     Grant, Caroline A. and Schmutz, Beat and Steck, Roland and Schuetz, Michael and Epari, Devakara R. (2009) Creation of a validated 3D finite-element model of an ovine tibia. In: 4th Asia Pacific Biomechanics Conference, 14-17 April 2009, University of Canterbury, Christchurch.      © Copyright 2009 [please consult the author]   Creation of a validated 3D finite element model of an ovine tibia Caroline A. GRANT1,2, Beat SCHMUTZ2, Roland STECK2, Michael SCHUETZ2, Devakara R. EPARI2 1Paediatric Critical Care Research Group, Paediatric Intensive Care Unit, Mater Children’s Hospital, South Brisbane, Queensland 2Orthopaedics & Trauma Qld, Institute of Health and Biomedical Innovation,  Queensland University of Technology, Brisbane, Queensland E-mail: c.grant@student.qut.edu.au  Abstract Ovine models are widely used in orthopaedics and trauma research. We present the development and validation of an FE model of an ovine tibia for use in the testing of tibia fracture fixation plates. The FE model was generated from CT data of a cadaveric tibia and validated by mechanical testing of the bone.  An offset 3-pt bend test was conducted with strain gauges placed on the anterior and posterior surfaces of the diaphysis.  The loads applied during testing were applied to the model after digitising their location and orientation with a 3D digitiser.  A comparison of the surface strains was conducted.  Initial results show a good correlation between the mechanical test and the FE model with calculated strain values within 2% of the measured strains. Further improvements are expected with the incorporation of bone density-specific material properties in the model. Key words: Finite Element Analysis, Mechanical testing, Ovine Tibia, CT, Orthopaedic implant, Fracture fixation plate   1. Introduction Ovine models are widely used in orthopaedics and trauma research. However data recorded during mechanical testing is limited in detail and can only tell us so much about the behaviour of the bone.  3D finite element (FE) models of bones generate highly detailed outputs and allow the local mechanical environment to be determined both internally and externally under complex loading scenarios.  A formal validation of the FE model with mechanical testing is essential for further use.  We present the development and validation of an FE model of an ovine tibia for use in the testing of tibia fracture fixation plates. 2. Methods 2.1 Mechanical Testing Mechanical testing of the tibia was conducted in a manner that could be replicated in the computational model.  Strain gauges were attached to the anterior and posterior surfaces of the cleaned bone, and an offset 3-pt bend test was conducted. A preload of 50 N was applied followed by three cycles of loading to 350 N. Load/displacement data was recorded throughout the test along with strain information (Table 1). To accurately reproduce this test in the FE model and compare strain results, information was required on the exact orientation of the bone within the rig, the position and angle of the loads applied and the position of the strain gauges.  This data was acquired using a FARO arm 3D digitiser (FARO Technology Inc) after the preload had been applied.  The solid model was then aligned with the positional data from the testing using a surface registration algorithm in the software package Rapidform (INUS Technology).   2.2 Model Creation The FE model was created from Computer Tomography data and then validated by mechanical testing.  A cadaveric ovine tibia was CT scanned and a 3D computer solid model generated using the software packages Amira (Mercury Computer Systems) and Geomagic (Raindrop Geomagic). Using Abaqus (Simula) an FE model was then generated from the solid model. Homogeneous material properties were applied to the bone.  A tetrahedral mesh was applied and the bone constrained and loaded in an offset 3-pt bend test.  A point load of 350 N was applied to the model with the bone constrained in x, y and z at one support and in y and z at the other, allowing the bone to move along its length during the bending. Resultant peak surface strains were recorded at the locations of the strain gauges in the mechanical test as determined with the FARO arm (Table 1). 3. Results Comparison of the results from the mechanical testing and the finite element modeling showed good correlation in the surface strains.  Values from nodes in the FE model at the locations of the anterior and posterior strain gauges were 11% larger and 5% larger respectively than the values recorded from the gauges themselves.  Displacement of the load was also measured, in the mechanical testing a total displacement of 0.79 mm was recorded of which 0.38 mm was recorded during the preload, the FE model underwent a displacement of 0.50 mm in a similar location with a 350 N load applied.    Mechanical Testing Finite Element ModelAnterior -1.44 E+03 με -1.60 E+03 με Posterior 1.56 E+03 με 1.64 E+03 με Displacement -0.79 mm total -0.38mm preload -0.50mm Table 1 Surface Strains recorded during a 3-pt bend mechanical test and the same test simulated using a finite element model 4. Discussion In this study our aim was to develop and validate an FE model of an ovine tibia. Good agreement between the model and the experiment was achieved with a difference in strain of approximately 10%. This discrepancy could be attributed to a combination of a number of different factors; use of a cortical shell model, homogeneous material property assignment, boundary condition application and the assumption of linear elasticity are all likely to have contributed. In the mechanical testing component a 3-pt bend test was chosen as the initial load case as it generates a range of compressive and tensile strains across the bone.   5. Further Work Subsequent model iterations will integrate CT based material property assignment.  By deriving the material properties from the CT data a heterogeneous map of values can be applied across the bone.  The methods of material property derivation from CT however will require close examination as currently established relationships have been validated for use with human rather than ovine bone. Additional loading environments, particularly those that are physiologically and clinically relevant will also be explored.  Further testing will also incorporate additional surface strain recording to facilitate validation of larger areas of the model. 

Creation of a validated 3D finite-element model of an ovine tibia

Ovine models are widely used in orthopaedics and trauma research. We present the development and validation of an FE model of an ovine tibia for use in the testing of tibia fracture fixation plates. The FE model was generated from CT data of a cadaveric tibia and validated by mechanical testing of the bone.  An offset 3-pt bend test was conducted with strain gauges placed on the anterior and posterior surfaces of the diaphysis.  The loads applied during testing were applied to the model after digitising their location and orientation with a 3D digitiser.  A comparison of the surface strains was conducted.  Initial results show a good correlation between the mechanical test and the FE model with calculated strain values within 2% of the measured strains. Further improvements are expected with the incorporation of bone density-specific material properties in the model

Name not available

Introduction Ovine models are widely used in orthopaedic research. To better understand the impact of orthopaedic procedures computer simulations are necessary. 3D finite element (FE) models of bones allow implant designs to be investigated mechanically, thereby reducing mechanical testing. Hypothesis We present the development and validation of an ovine tibia FE model for use in the analysis of tibia fracture fixation plates. Material &amp; Methods Mechanical testing of the tibia consisted of an offset 3-pt bend test with three repetitions of loading to 350N and return to 50N. Tri-axial stacked strain gauges were applied to the anterior and posterior surfaces of the bone and two rigid bodies – consisting of eight infrared active markers, were attached to the ends of the tibia. Positional measurements were taken with a FARO arm 3D digitiser. The FE model was constructed with both geometry and material properties derived from CT images of the bone. The elasticity-density relationship used for material property determination was validated separately using mechanical testing. This model was then transformed to the same coordinate system as the in vitro mechanical test and loads applied. Results Comparison between the mechanical testing and the FE model showed good correlation in surface strains (difference: anterior 2.3%, posterior 3.2%). Discussion &amp; Conclusion This method of model creation provides a simple method for generating subject specific FE models from CT scans. The use of the CT data set for both the geometry and the material properties ensures a more accurate representation of the specific bone. This is reflected in the similarity of the surface strain results

TEMPLATE FOR ABSTRACT SUBMISSION ISFR 2010 26-29 September 2010 Lords Cricket Grounds, London  TITLE CREATION OF A VALIDATED 3D FINITE ELEMENT MODEL OF AN OVINE TIBIA Authors and Affiliation Caroline A. GRANT, Beat SCHMUTZ, Roland STECK, Michael SCHUETZ, Devakara R. EPARI Orthopaedics and Trauma Queensland, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia  Introduction Ovine models are widely used in orthopaedic research. To better understand the impact of orthopaedic procedures computer simulations are necessary. 3D finite element (FE) models of bones allow implant designs to be investigated mechanically, thereby reducing mechanical testing.  Hypothesis We present the development and validation of an ovine tibia FE model for use in the analysis of tibia fracture fixation plates.  Material & Methods Mechanical testing of the tibia consisted of an offset 3-pt bend test with three repetitions of loading to 350N and return to 50N. Tri-axial stacked strain gauges were applied to the anterior and posterior surfaces of the bone and two rigid bodies – consisting of eight infrared active markers, were attached to the ends of the tibia. Positional measurements were taken with a FARO arm 3D digitiser.  The FE model was constructed with both geometry and material properties derived from CT images of the bone.  The elasticity-density relationship used for material property determination was validated separately using mechanical testing.   This model was then transformed to the same coordinate system as the in vitro mechanical test and loads applied.  Results Comparison between the mechanical testing and the FE model showed good correlation in surface strains (difference: anterior 2.3%, posterior 3.2%).   Discussion & Conclusion This method of model creation provides a simple method for generating subject specific FE models from CT scans.  The use of the CT data set for both the geometry and the material properties ensures a more accurate representation of the specific bone. This is reflected in the similarity of the surface strain results.  

English

Creation of a validated 3D finite element model of an ovine tibia

Introduction\ud
Ovine models are widely used in orthopaedic research. To better understand the impact of orthopaedic procedures computer simulations are necessary. 3D finite element (FE) models of bones allow implant designs to be investigated mechanically, thereby reducing mechanical testing.\ud
\ud
Hypothesis\ud
We present the development and validation of an ovine tibia FE model for use in the analysis of tibia fracture fixation plates.\ud
\ud
Material & Methods\ud
Mechanical testing of the tibia consisted of an offset 3-pt bend test with three repetitions of loading to 350N and return to 50N. Tri-axial stacked strain gauges were applied to the anterior and posterior surfaces of the bone and two rigid bodies – consisting of eight infrared active markers, were attached to the ends of the tibia. Positional measurements were taken with a FARO arm 3D digitiser.\ud
\ud
The FE model was constructed with both geometry and material properties derived from CT images of the bone.  The elasticity-density relationship used for material property determination was validated separately using mechanical testing.   This model was then transformed to the same coordinate system as the in vitro mechanical test and loads applied.\ud
\ud
Results\ud
Comparison between the mechanical testing and the FE model showed good correlation in surface strains (difference: anterior 2.3%, posterior 3.2%). \ud
\ud
Discussion & Conclusion\ud
This method of model creation provides a simple method for generating subject specific FE models from CT scans.  The use of the CT data set for both the geometry and the material properties ensures a more accurate representation of the specific bone. This is reflected in the similarity of the surface strain results.\u

Creation of a validated 3D finite-element model of an ovine tibia

Abstract

Similar works

Full text

Available Versions

Queensland University of Technology ePrints Archive

Name not available

Queensland University of Technology ePrints Archive

Name not available