Sustained spinal cord compression: part I: time-dependent effect on long-term pathophysiology.

Abstract

BACKGROUND: The objective of this study is to determine whether there is a relationship between the duration of sustained spinal cord compression and the extent of spinal cord injury and the capacity for functional recovery after decompression. METHODS: Sixteen dogs underwent sustained spinal cord compression for thirty or 180 minutes. The cords were compressed with use of a loading device with a hydraulic piston. A pressure transducer was attached to the surface of the piston, which transmitted real-time spinal cord interface pressures to a data-acquisition system. Somatosensory evoked potentials were monitored during a sixty-minute recovery period as well as at twenty-eight days after the injury. Functional motor recovery was judged throughout a twenty-six-day period after the injury with use of a battery of motor tasks. The volume of the lesion and damage to the tissue were assessed with both magnetic resonance imaging and histological analysis. RESULTS: Sustained spinal cord compression was associated with a gradual decline in interface pressure. Despite this, there was continuous decline in the amplitude of the somatosensory evoked potentials, which did not return until the cord was decompressed. Within one hour after the decompression, the dogs in the thirty-minute-compression group had recovery of somatosensory evoked potentials, but no animal had such recovery in the 180-minute group. Recovery of the somatosensory evoked potentials in the thirty-minute group was sustained over the twenty-eight days after the injury. Motor tests demonstrated rapid recovery of hindlimb motor function in the thirty-minute group, but there was considerable impairment in the 180-minute group. Within two weeks after the injury, balance, cadence, stair-climbing, and the ability to walk up an inclined plane were significantly better in the thirty-minute group than in the 180-minute group. The longer duration of compression produced lesions of significantly greater volume, which corresponded to the long-term functional outcome. CONCLUSIONS: The relatively rapid viscoelastic relaxation of the spinal cord during the early phase of sustained cord compression suggests that there are mechanisms of secondary injury that are linked to tissue displacement. Longer periods of displacement allow propagation of the secondary injury process, resulting in a lack of recovery of somatosensory evoked potentials, limited functional recovery, and more extensive tissue damage.