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A Model of Experimental Spinal Cord Trauma Based on Computer-Controlled Intervertebral Distraction: Characterization of Graded Injury

Dabney, Kirk W. MD*; Ehrenshteyn, Marina MS*; Agresta, Cynthia A. BS*; Twiss, Jeffery L. MD, PhD†; Stern, Garland PhD*; Tice, Lisa MS*; Salzman, Steven K. PhD*‡

Spine:
Basic Science
Abstract

Study Design. A new model of experimental spinal cord injury is detailed based on the application of tensile (distraction) force to the vertebral column of the rat.

Objectives. To develop an experimental model of graded spinal cord injury by application of tensile forces to the vertebral column.

Summary of Background Data. Distraction is frequently an integral component of human spinal cord injury, but the acute application of tensile forces to the spinal cord has not been modeled rigorously.

Methods. A computer-controlled, motorized outrigger device was used to apply a longitudinal stretching force to sublaminar hooks oriented proximally at T9 and distally at T11. Distraction force was applied using a program that varied the length, speed, and duration of its distraction. A modified 14-point Tarlov score was used to establish the presence of hindlimb dysfunction. This score was correlated with acute changes in somatosensory-evoked potential amplitude, the comprehensive open-field test of locomotor function at 4 weeks, and postmortem measurements of serotonin content and metabolism in spinal cord rostral and distal to the site of injury.

Results. Of distraction parameters, only length of distraction correlated significantly with each outcome measure. For outcome measures, open-field test inventory and distal/proximal ratio of the spinal content of serotonin were correlated most closely with final Tarlov scores. Acute somatosensory-evoked potential amplitudes proved to be an excellent index of the acute injury but were poor measures of long-term outcome.

Conclusions. Distraction-induced spinal cord injury was uniformly mild in rats with intact facet capsular ligaments, regardless of distraction parameters. Cutting the facet joint ligaments consistently generated outcome measures associated with mild, moderate, and severe spinal cord injury at 3-, 5-, and 7-mm distraction lengths, respectively.

In Brief

Tensile forces frequently accompany human spinal cord injury, but experimental models of such distraction injury are rare. A model of acute spinal cord injury by distraction of the spinal cord between T9 and T11 is described. Varying distraction length consistently generated a graded injury in animals that had their facet ligaments cut before distraction. According to a modified Tarlov score, open-field test parameters, and postmortem biochemical assessment of serotonin and 5-hydroxy-indole-3-acetic acid levels, animals that underwent distraction at 5 mm/sec for a 5-second duration over 3-, 5-, and 7-mm distances segregated into mild, moderate, and severe injury categories, respectively.

Author Information

From the *Spinal Trauma Research Laboratory, Nemours Biomedical Research, and Department of Orthopaedic Surgery, Nemours Children's Clinic-Wilmington, Alfred I. duPont Hospital for Children, Wilmington, Delaware, and the †Neuroscience Research Laboratory, Nemours Biomedical Research, Alfred I. duPont Hospital for Children, Wilmington, Delaware.

‡Deceased.

Supported by funds from the Orthopedic Research Education Foundation, the Nemours Foundation (to KWD), and programmatic funds from Nemours Biomedical Research (to SKS and JLT).

Acknowledgment date: March 5, 2003. First revision date: November 14, 2003. Acceptance date: December 22, 2003.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Foundation funds were received to support this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Kirk W. Dabney, MD, Department of Orthopaedic Surgery, NCC-Wilmington, Alfred I. duPont Hospital for Children, 1600 Rockland Road, Wilmington, DE 19803; E-mail: kdabney@nemours.org

© 2004 Lippincott Williams & Wilkins, Inc.