A model of experimental spinal cord trauma based on computer-controlled intervertebral distraction: characterization of graded injury.

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.