title: The effects of spinal cord injury induced by shortening on motor evoked potentials and spinal cord blood flow: an experimental study in Swine.
abstract: BACKGROUND
  Spinal cord injury due to spinal shortening is disastrous, but the amount that the spine can be shortened without injury is unknown. We assessed spinal cord injury and changes in spinal cord blood flow after spinal shortening in swine.
  
  
  METHODS
  Ten pigs underwent pedicle screw instrumentation between T10 and T13 followed by a T11 and T12 vertebrectomy resulting in spinal shortening. Spinal cord function and spinal cord blood flow were monitored simultaneously with use of transcranial motor evoked potentials and laser Doppler flowmetry, respectively. A staged shortening procedure was performed: phase 1 resulted in no morphological change in the spinal cord, phase 2 resulted in buckling of the spinal cord, and phase 3 resulted in kinking of the spinal cord. After loss of motor evoked potential signals, which was considered to indicate spinal cord injury, the spinal instrumentation was tightened. The motor evoked potentials and spinal cord blood flow were monitored for an additional thirty minutes, and a wake-up test was then performed. Finally, a spinal cord specimen was obtained and evaluated histologically.
  
  
  RESULTS
  The motor evoked potential data demonstrated no evidence of spinal cord injury during phases 1 and 2. However, the signals were lost during phase 3, indicating spinal cord injury. The mean shortening was 35 ± 2.7 mm, which was similar to the mean vertebral body height at the thoracolumbar level (33.6 ± 1.9 mm), indicating that spinal cord injury resulted from shortening equivalent to the height of one vertebra. Spinal shortening did not cause injury if the amount of shortening was less than the mean segmental height of the entire spinal column (27.7 ± 1.6 mm for T1-L6). The spinal cord blood flow increased slightly (by 11.6% ± 20.6%) during phase 2, but decreased by 43.1% ± 11.4% during phase 3. The wake-up test performed after thirty minutes revealed no movement in the lower limbs.
  
  
  CONCLUSIONS
  Spinal shortening of =104.2% of one vertebral body height at the thoracolumbar level caused spinal cord injury, but shortening of =73.8% did not result in injury. swine.
authors: Department of Orthopedics, Korea University Guro Hospital, Seoul, South Korea.
authors: Hitesh N
authors: HN
authors: Modi
authors: Seung-Woo
authors: SW
authors: Suh
authors: Jae-Young
authors: JY
authors: Hong
authors: Jae-Hyuk
authors: JH
authors: Yang
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D019054:Evoked Potentials, Motor / Q000502:physiology*; D050815:Fractures, Compression / Q000150:complications / Q000473:pathology / Q000503:physiopathology; D012039:Regional Blood Flow / Q000502:physiology*; D013116:Spinal Cord / Q000098:blood supply* / Q000473:pathology / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology*; D013552:Swine; D013904:Thoracic Vertebrae / Q000601:surgery