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Design Innovation Paper

Characterization of a Novel, Magnetic Resonance Imaging-Compatible Rodent Model Spinal Cord Injury Device

[+] Author and Article Information
Tim Bhatnagar

Department of Mechanical Engineering,
University of British Columbia,
Vancouver, BC V6T 1Z4, Canada
International Collaboration
on Repair Discoveries (ICORD),
Vancouver, BC V5Z 1M9, Canada
e-mail: tim.bhatnagar@gmail.com

Jie Liu

Department of Zoology, University of British Columbia,
Vancouver, BC V6T 1Z4, Canada
International Collaboration
on Repair Discoveries (ICORD),
Vancouver, BC V5Z 1M9, Canada

Thomas Oxland

Departments of Orthopaedics and Mechanical Engineering,
University of British Columbia,
Vancouver, BC V6T 1Z4, Canada
International Collaboration on
Repair Discoveries (ICORD),
Vancouver, BC V5Z 1M9, Canada

1Corresponding author.

Manuscript received January 27, 2014; final manuscript received April 16, 2014; accepted manuscript posted May 14, 2014; published online June 26, 2014. Assoc. Editor: Barclay Morrison.

J Biomech Eng 136(9), 095001 (Jun 26, 2014) (6 pages) Paper No: BIO-14-1053; doi: 10.1115/1.4027670 History: Received January 27, 2014; Revised April 16, 2014; Accepted May 14, 2014

Rodent models of acute spinal cord injury (SCI) are often used to investigate the effects of injury mechanism, injury speed, and cord displacement magnitude, on the ensuing cascade of biological damage in the cord. However, due to its small size, experimental observations have largely been limited to the gross response of the cord. To properly understand the relationship between mechanical stimulus and biological damage, more information is needed about how the constituent tissues of the cord (i.e., gray and white matter) respond to injurious stimuli. To address this limitation, we developed a novel magnetic resonance imaging (MRI)-compatible test apparatus that can impose either a contusion-type or dislocation-type acute cervical SCI in a rodent model and facilitate MR-imaging of the cervical spinal cord in a 7 T MR scanner. In this study, we present the experimental performance parameters of the MR rig. Utilizing cadaveric specimens and static radiographs, we report contusion magnitude accuracy that for a desired 1.8 mm injury, a nominal 1.78 mm injury (SD = 0.12 mm) was achieved. High-speed video analysis was employed to determine the injury speeds for both mechanisms and were found to be 1147 mm/s (SD = 240 mm/s) and 184 mm/s (SD = 101 mm/s) for contusion and dislocation injuries, respectively. Furthermore, we present qualitative pilot data from a cadaveric trial, employing the MR rig, to show the expected results from future studies.

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Figures

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Fig. 6

Measurement of dislocation injury (DL) displacement using HS video. The displacement of the caudal set of clamps is tracked (left, initial position; right, final position—2.5 mm), and the average speed is determined by dividing the displacement by the time required to complete the injury (∼13.6 ms). The cranial (“Cr”) and caudal (“Ca”) directions are indicated.

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Fig. 7

Injury speeds as a function of actuator inlet pressure. (a) Regression analysis of the contusion injury impact speed against actuator inlet pressure shows a relationship over a wide pressure range [R12 (black); 21–88 psi] but no discernible relationship within the experimental pressure range [R22 (red); 78–88 psi]; (b) the same analysis for average dislocation injury speed against actuator inlet pressure indicated that within the pressure ranges specified, the change in inlet pressure did not have a predictable effect on the injury speeds.

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Fig. 8

Sample images using the MR rig—pre-injury. The MR rig facilitates imaging of the in vivo rodent spinal cord, with differentiation between the white and the gray matter of the cord. Sample cross-sectional slices are shown from different parts of the cord along the intended injury area (marked by the white, solid line in the sagittal view image).

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Fig. 9

Sample images using the MR rig—during injury. The 2.5 mm dislocation injury is easily visualized in the sagittal view. The representative cross-sectional slices (taken from the same levels as in the pre-injury scan) clearly show local deformation of the white and gray matter due to the dislocation injury.

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Fig. 5

Sample static X-ray images to determine contusion injury displacement magnitude. (a) The dorsoventral (DV) diameter of the spinal canal is measured (shown in red) and used as an approximate DV-diameter of the spinal cord; (b) the 2 mm spherical impactor is used as a gauge-length for pixel-mm measurement conversion; (c) once the contusion injury is actuated, a final X-ray is used to determine the remaining distance between the tip of the spherical impactor and the ventral wall of the spinal canal.

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Fig. 4

Schematic diagram of the dislocation setup. (a) The caudal clamp mount links the caudal dislocation clamp (attached to C6–C7) to the actuating piston. The piston travel length (i.e., the dislocation magnitude—2.5 mm) is limited by the insertion of a spacing block (brown), between the caudal assembly and the pneumatic actuator (dark gray). The red box highlights the cervical spine linked to the apparatus; (b) actuation of the piston causes the caudal assembly to dorsally translate, relative to the fixed cranial assembly, until the spacing block prevents further motion; (c) a detailed view of the imposed dislocation injury with the cranial clamps (red) fixed and anatomical directions indicated: D—dorsal, V—ventral, C—caudal, Cr—cranial.

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Fig. 3

Schematic diagram of the contusion injury. (a) The contusion clamps attach rigidly to the cervical spine and the laminectomy at C5/6 is centered beneath the contusion impactor, which is driven into the dorsal surface of the spinal cord by the pneumatic actuator (dark gray); (b) the contusion clamps attach to vertebrae C4–C7 via the lateral notches of the spine.

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Fig. 2

Custom designed spinal clamps to facilitate SCI. (a) Custom contusion injury clamps; (b) one set of the pair of identical, custom dislocation clamps that are used to create a dislocation injury.

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Fig. 1

The novel MR rig. (a) For MR image acquisition, the specimen is loaded into the MR rig and is placed at the center of the bore of the MR scanner—represented by the cylindrical cut-away. The “air line” (blue) supplies the pneumatic actuator (dark gray) with pressurized air from outside the MR scanner. The red box outlines the portion of the MR rig shown in (b) and (c); (b) the MR rig contusion configuration with clamps attached to the cervical spine of a specimen; (c) the MR rig dislocation configuration with clamps attached to the cervical spine of a specimen.

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