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Research Papers

On Colles’ Fracture: An Experimental Study Involving Structural and Material Testing

[+] Author and Article Information
K. Gdela

Department of Civil Engineering, McMaster University, Hamilton, ON, Canada, L8S 4L7

S. Pietruszczak1

Department of Civil Engineering, McMaster University, Hamilton, ON, Canada, L8S 4L7pietrusz@mcmaster.ca

P. V. Lade, P. Tsopelas

Department of Civil Engineering, The Catholic University of America, Washington, DC 20064

1

Corresponding author.

J. Appl. Mech 75(3), 031002 (Mar 05, 2008) (10 pages) doi:10.1115/1.2839902 History: Received December 18, 2006; Revised November 08, 2007; Published March 05, 2008

A two-stage experimental program was conducted, which was aimed at examining the process of initiation/propagation of fracture in human radii under the conditions simulating a fall onto an outstretched hand. It involved a number of destructive tests on dried cadaver bones. The bones were first subjected to DXA as well as spiral CT measurements to establish the density properties and the details of geometry. Subsequently, the specimens were tested under controlled boundary conditions, to induce Colles’ type of fracture. Following these tests, samples of cortical bone tissue were extracted at different orientations with respect to the direction of osteons and tested in axial tension. The results of material tests were used to verify the performance of an anisotropic fracture criterion for the cortical tissue. It has been demonstrated that the proposed criterion can reproduce the basic trends in the directional dependence of the tensile strength characteristics. For the structural tests, a correlation was established between the geometric characteristics of the cortex, the strength properties and the fracture load for individual radii that were tested. It was shown that the morphological traits and/or the strength properties alone are not adequate predictors of the fracture load of intact radii. A rational assessment of the fracture load requires a mechanical analysis that incorporates the key elements of the experimental program outlined here, i.e., the information on bone geometry, material properties of the bone tissue, and the static/kinematic boundary conditions. A preliminary example of a finite element analysis, for one of the radii bones tested, has been provided.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic representation of cortical bone sample; xi - material coordinate system; x¯i - global coordinate system. (Note: α defines the inclination of the critical plane with respect to horizontal axis, while β specifies the orientation of osteons)

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Figure 2

CT scans of two isolated radii together with vials containing calibration solutions for the derivation of Hounsfield number

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Figure 4

Experimental setup for material tests (longitudinal sample, β=0deg)

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Figure 5

Orientation of fracture plane; (a) sample tested in longitudinal direction; (b) samples tested at 90deg and 45deg

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Figure 6

Failure mode for Bone 5; (a) anterior posterior view; (b) posterior anterior view

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Figure 7

Load-displacement characteristic for Bone 5

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Figure 8

Typical stress-strain curves representative of tensile tests for cortical tissue

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Figure 9

Numerical simulation of direct tension test; Bone 5, ĉ=74.86MPa, Ω1=1.400. (a) Distribution of axial tensile strength; (b) orientation of fracture plane.

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Figure 10

Numerical simulation of direct tension test; Bone 9, ĉ=55.21MPa, Ω1=1.444. (a) Distribution of axial tensile strength; (b) orientation of fracture plane

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Figure 3

Experimental setup for testing Colles’ fracture; two different samples shown in (a) lateral medial view (b) palmer view. Load cell at the top of the figure.

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Figure 11

Numerical simulation of direct tension test; Bone 11, c0=64.28MPa, Ω1=1.379. (a) Distribution of axial tensile strength, (b) orientation of fracture plane, and (c) distribution of axial tensile strength - polar coordinate representation

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Figure 12

Correlation between the tensile strength predicted by the model and the experimental results (excludes samples that were used for the calibration of the model). Note: the dashed line is a reference line illustrating perfect agreement; the solid line is the actual regression line forced through zero.

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Figure 13

Correlation between the tensile strength in longitudinal direction, as predicted by the model, and volumetric BMD of cortical tissue

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Figure 14

Correlation between the ultimate load and clinical/geometric measurements

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Figure 15

Failure mode for the radius Bone 5: right: experimental result; left: FE simulation; distribution of failure function (darkened zone shows the region where the onset of tensile fracture occurs)

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