Effects of Compression on Physiologic Integrity of the Spinal Cord, on Circulation, and Clinical Status in Four Different Directions of Compression

The authors investigated the effects of focal compression on physiologic integrity; somatosensory evoked potentials, neurogenic motor evoked potentials and spine-to-spine potentials, on spinal cord circulation and clinical status in four different type of compression; posterior, anterior, circumferential, and lateral in 31 pigs. Spine-to-spine potentials degraded earlier in amplitude than somatosensory evoked and motor evoked potentials regardless of direction of compression. The first lost potential was the somatosensory evoked one during posterior, circumferential, and lateral compression and motor evoked potentials during anterior compression. Somatosensory evoked potential was the only wave to detect the side of lateral compression. Following release of compression somatosensory evoked potentials and motor evoked potentials returned almost to 100% in amplitude, whereas spine-to-spine potentials recovered to approximately 50%. At that time all animals showed grossly normal motion in hind-limb, therefore spine-to-spine potentials might be too sensitive to motor function. Spine-to-spine potentials should contain more tracts than either somatosensory evoked potentials or motor evoked potentials. Somatosensory evoked potentials probably show more posterior part, whereas motor evoked potentials do more of the anterior part of the spinal cord. The spinal cord revealed a complete ischemia regardless of direction of compression when at least one potential was gone, however it regained the shape and perfusion following release of compression although there were some hemorrhagic contusions remaining. These suggest that ischemic changes may play some part in degradation of potentials, however it does not influence much the recovery following release of compression because it regains quickly. The final recovery depends on the complication.