Cord/spine motion in experimental spinal cord injury

We examined cord motion and cord-spine coupling associated with the axial tension and dorsal impact models of spinal cord injury. In 20 cats, distraction forces up to 15 kg were applied. Five microliters of radiopaque agent was injected into the central cord at C4-C7 (14 cats) and T6-L1 (6 cats) at 2-mm intervals. In 20 cats, 300 g/cm impacts were delivered after injection of contrast at 2-mm intervals from the impact point. Trials were conducted under fluoroscopy. At 5-kg distraction, vertebral motion averaged 2.12 mm and cord motion averaged 1.03 mm (coupling ratio = .49). At 10-kg coupling increased to .75. Between 10 and 15-kg distraction, the amount of increase in cord length slowed, as did the ratio (.59). Differences in length between load groups were significant at most levels, and motion corresponded with histologic injury reported previously. In the thoracolumbar region, minimal spine motion and no cord motion occurred. Spine motion was not seen with dorsal impact although cord motion at 2 mm from impact averaged 1.3 mm/300 g/cm, which decreased away from the impact point. The spinal cord has limited elasticity, which may be related to injury. Because spine and cord motion occur in clinical injury, experimental models need to incorporate this element.