A Removable Precision Device for In-Vivo Mechanical Compression of Rat Tail Intervertebral Discs

[+] Author and Article Information
Justin M. Stinnett-Donnelly, Jeffrey J. MacLean

School of Engineering, College of Engineering and Mathematical Sciences, Burlington, VT 05405

James C. Iatridis

School of Engineering, College of Engineering and Mathematical Sciences, Burlington, VT 05405james.iatridis@uvm.edu

J. Med. Devices 1(1), 56-61 (Aug 14, 2006) (6 pages) doi:10.1115/1.2355692 History: Received April 08, 2006; Revised August 14, 2006

The rat tail intervertebral disc has emerged as an important model to examine the mechanisms for mechanically induced degeneration and remodeling. Previous methods used to apply high precision axial compressive loading to a rat tail intervertebral disc in vivo either required anesthesia, or the permanent mounting of a loading device to the animal, and were not well described in the literature. Therefore, a new device to apply compressive loading to the rat tail intervertebral disc was developed and validated. The rat tail compressive loading system utilized a pneumatically driven device weighing 18g, and was capable of delivering a 12.6N sinusoidal or square waveform at frequencies up to 1.0Hz. The system improved on previous methods in its modular construction, relative ease of fabrication, compatibility with existing tail model technology and overall cost effectiveness. The removable system eliminated the need for anesthesia and through a modular, cost effective, design allowed for the simultaneous loading of multiple animals. This system expanded the ability to accurately, ethically, and efficiently apply dynamic compressive loads to the rat tail intervertebral disc for extended periods of time in order to address questions related to disc mechanobiology.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

A modified Ilizarov type ring holder for the alignment jig is compatible with the modified ring design. Only two screws were required allowing for efficient installation and removal of rings during surgery. The alignment jig insured parallelism of the rings during the pinning procedure.

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Figure 2

(a) A schematic of the rat tail compressive device showing the various components. (b) A photograph of the device attached to two implanted Ilizarov type carbon fiber (CF) rings.

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Figure 3

Schematic of the pneumatic system layout where one control valve feeds four mechanical devices. Acetyl quick connects allow individual devices to be isolated form the pneumatic system and swivels allow tubing to rotate as the animal turns around multiple times.

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Figure 4

A load cell adaptor was used to transfer axial force generated by the device through aluminum adaptors to a 10lb load cell.

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Figure 5

Representative frequency spectrum for devices 7–10 for (a) force time waveform, (b) frequencies from 0to10Hz and (c) frequencies 10–500Hz shows that the four devices yield a highly sinusoidal waveform with similar spectrums while producing a 1.0Hz12.6N sinusoidal force. Note that the y-scale power in (c) is several orders of magnitude lower than in (b). All other devices behaved similarly.




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