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Technical Brief

Repeatability of a Dislocation Spinal Cord Injury Model in a Rat—A High-Speed Biomechanical Analysis

[+] Author and Article Information
Stephen Mattucci

Orthopaedic and Injury Biomechanics Group,
Departments of Orthopaedics and Mechanical Engineering,
International Collaboration on Repair Discoveries,
University of British Columbia,
818 West 10th Avenue,
Vancouver, BC V5Z 1M9, Canada
e-mail: mattucci.stephen@gmail.com

Jie Liu

International Collaboration on Repair Discoveries,
University of British Columbia,
818 West 10th Avenue,
Vancouver, BC V5Z 1M9, Canada
e-mail: jliu@icord.org

Paul Fijal

Orthopaedic and Injury Biomechanics Group,
Departments of Orthopaedics and Mechanical Engineering,
International Collaboration on Repair Discoveries,
University of British Columbia,
818 West 10th Avenue,
Vancouver, BC V5Z 1M9, Canada
e-mail: paul@awakelabs.com

Wolfram Tetzlaff

International Collaboration on Repair Discoveries,
University of British Columbia,
818 West 10th Avenue,
Vancouver, BC V5Z 1M9, Canada
e-mail: tetzlaff@icord.org

Thomas R. Oxland

Professor and Director
Orthopaedic and Injury Biomechanics Group,
Departments of Orthopaedics and Mechanical Engineering,
International Collaboration on Repair Discoveries,
University of British Columbia,
818 West 10th Avenue,
Vancouver, BC V5Z 1M9, Canada
e-mail: toxland@icord.org

1Corresponding author.

Manuscript received March 16, 2017; final manuscript received May 30, 2017; published online August 3, 2017. Assoc. Editor: James C Iatridis.

J Biomech Eng 139(10), 104501 (Aug 03, 2017) (8 pages) Paper No: BIO-17-1113; doi: 10.1115/1.4037224 History: Received March 16, 2017; Revised May 30, 2017

Dislocation is the most common, and severe, spinal cord injury (SCI) mechanism in humans, yet there are few preclinical models. While dislocation in the rat model has been shown to produce unique outcomes, like other closed column models it exhibits higher outcome variability. Refinement of the dislocation model will enhance the testing of neuroprotective strategies, further biomechanical understanding, and guide therapeutic decisions. The overall objective of this study is to improve biomechanical repeatability of a dislocation SCI model in the rat, through the following specific aims: (i) design new injury clamps that pivot and self-align to the vertebrae; (ii) measure intervertebral kinematics during injury using the existing and redesigned clamps; and (iii) compare relative motion at the vertebrae–clamp interface to determine which clamps provide the most rigid connection. Novel clamps that pivot and self-align were developed based on the quantitative rat vertebral anatomy. A dislocation injury was produced in 34 rats at C4/C5 using either the existing or redesigned clamps, and a high-speed X-ray device recorded the kinematics. Relative motion between the caudal clamp and C5 was significantly greater in the existing clamps compared to the redesigned clamps in dorsoventral translation and sagittal rotation. This study demonstrates that relative motions can be of magnitudes that likely affect injury outcomes. We recommend such biomechanical analyses be applied to other SCI models when repeatability is an issue. For this dislocation model, the results show the importance of using clamps that pivot and self-align to the vertebrae.

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Figures

Grahic Jump Location
Fig. 1

Original dislocation clamps [17]. (a) Transverse view of clamp holding vertebra, where clamp grips vertebra in the lateral groove between the transverse process and facet joints. (b) Sagittal view of the clamp.

Grahic Jump Location
Fig. 2

(a) The lateral ridge between the articular and transverse process. This ridge runs the length of the cervical spine and is where the injury clamps are tightened. (b) Existing injury clamps tightening to hold two vertebrae. Since the vertebrae are different widths, the clamps can only securely hold one vertebra, allowing the narrower vertebra to move.

Grahic Jump Location
Fig. 3

Self-aligning dislocation injury clamps. (a) Clamp arm pivoting about dorsoventral axis. (b) Saddle washer slides on exterior surface of the clamp which enables clamp arm to pivot. Three positions are shown. (c) Dimensioned front view of clamp holding C5. (d) Front-bottom view of clamp simultaneously holding C5 and C6. (e) Photo of clamp prototype. Saddle washers are constructed out of polyether ether ketone to reduce friction at the interface and remain aligned during tightening.

Grahic Jump Location
Fig. 4

Schematic of the location of the fiducial markers on the vertebrae and injury clamps, with a corresponding high-speed X-ray image. The clamps are represented as outlines on the schematic to visualize the marker locations on the vertebrae. The rostral clamp was held rigid, while the caudal clamp was dislocated dorsally.

Grahic Jump Location
Fig. 5

Experimental setup of the UBC multimechanism SCI apparatus within the X-ray system: (a) X-ray source, (b) X-ray image intensifier, (c) electromagnetic actuator, (d) rat (model), (e) stereotaxic frame, and (f) dislocation injury clamps

Grahic Jump Location
Fig. 6

The true measure of the dislocation injury parameter: motion of C5 with respect to C4. The existing clamps had a displacement range of 1.1–2.2 mm, while the self-alignment clamps had a range of 1.5–1.9 mm.

Grahic Jump Location
Fig. 7

Relative motion compared between existing clamps (gray dashed line) and self-alignment clamps (black solid line). Slipping at the rostral–clamp interface was not significantly different between the clamps for both translation (a) and rotation (b). Slipping was most obvious at the caudal–clamp interface, and was significantly greater in the existing clamps for bothtranslation (c) and rotation (d). Importantly slipping only occurred in some instances with the existing clamps. The combined rotation of the two vertebrae experiencing the dislocation, C4 and C5: a measurement of maintained spinal canal integrity(e).

Grahic Jump Location
Fig. 8

(a) When the vertebrae rotate at the site of the dislocation, the canal remains open, with no physical insult on the cord. (b) When the vertebrae are restricted from rotation during the dislocation, the canal opening is reduced, causing a shearing or pinching force on the spinal cord.

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