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DESIGN INNOVATION

Radio-Translucent 3-Axis Mechanical Testing Rig for the Spine in Micro-CT

[+] Author and Article Information
K. M. Si-hoe

Center for Biomedical Materials Applications and Technology (BIOMAT), Department of Mechanical and Production Engineering,  National University of Singapore, Block E3, 05-15, 10 Kent Ridge Crescent, Singapore 119260kuanming@gmail.com

S. H. Teoh1

Center for Biomedical Materials Applications and Technology (BIOMAT), Department of Mechanical and Production Engineering,  National University of Singapore, Block E3, 05-15, 10 Kent Ridge Crescent, Singapore 119260mpetsh@nus.edu.sg

Jeremy Teo

Center for Biomedical Materials Applications and Technology (BIOMAT), Department of Mechanical and Production Engineering,  National University of Singapore, Block E3, 05-15, 10 Kent Ridge Crescent, Singapore 119260bietcmj@nus.edu.sg

1

Corresponding author.

J Biomech Eng 128(6), 957-964 (Jun 14, 2006) (8 pages) doi:10.1115/1.2375136 History: Received August 03, 2005; Revised June 14, 2006

To date, no apparatus has yet been devised which would allow the study of bone microstructure of the whole vertebrae under mechanical loading. This paper outlines the design and development of a 3-axis radio-translucent mechanical testing rig for spinal research and testing. This rig is to be used in conjunction with a Shimadzu micro-CT scanner. Several tests were conducted to verify the feasibility of the rig design. First, the maximum range of deformation in compression, flexion\extension, and lateral bending that could be exerted on a goat lumbar functional spinal unit was evaluated using the noncontact digital markers method. Stepwise compression loading was also conducted on a single porcine vertebra and the loading data was compared to results obtained from an industrial grade compression testing machine. Finally, micro-CT scans of a porcine vertebra prior to and at a compression failure strain were obtained. The rig was confirmed to be able to exert pure moment loading in the above mentioned modes of deformation and the extent of deformation was comparable to previous documented results. The stepwise compression loading conducted in the rig was also found to effectively approximate a continuous loading of the same specimen in an industrial grade compression testing machine. Finally, resultant micro-CT images of isotropic resolution 32.80μm of a porcine vertebra loaded in the rig were obtained. For the first time, trabecular microarchitecture detail of a whole vertebra buckling under 12.1% failure compression strain loading was studied using voxel-data visualization software. These initial series of tests verify the feasibility of the rig as an apparatus incorporating spinal testing and imaging.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

3D view of radio-translucent testing rig

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Figure 2

Biomechanical movements of the spine

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Figure 3

FEM analysis of Perspex tubing

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Figure 4

Deformation plate mechanism

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Figure 5

X‐Z translational disk with ball bearing design

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Figure 6

Short compression testing setup

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Figure 7

Digital Images of specimen under (a) right lateral bending, (b) flexion. The spatial coordinates of physical markers A, B, C, and D were used to calculate the deformation angles.

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Figure 8

Schematic of cone CT scanning setup

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Figure 12

Comparison chart showing (a) 3D volume rendering of C3 vertebra scans in unloaded (left) and loaded state (right), (b) cross section of vertebra along the frontal plane, (c) extracted 1mm thick slice with high bone microstructure detail

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Figure 9

Graphs depicting the relationship between coupled shear forces, applied moment, and resulting deformation angle for L1–L2 under (a) flexion, (b) extension, (c) left, and (d) right lateral bending. (x-compressive preload (N)Fz, ∎-lateral shear (N), Fx, ▴-antero-posterior shear, Fy,-applied moment (Nm), Mx, My).

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Figure 10

Comparison of stepwise and continuous loading of C3 porcine vertebra

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Figure 11

Micro-CT images of porcine vertebra in (a) dry condition, (b) wet condition

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