Background: The degree of canal stenosis following a thoracolumbar
burst fracture is sometimes used as an indication for decompressive surgery.
This study was performed to test the hypothesis that the final resting
positions of the bone fragments seen on computed tomography imaging are not
representative of the dynamic canal occlusion and associated neurological
damage that occurs during the fracture event.
Methods: A drop-weight method was used to create burst fractures in
bovine spinal segments devoid of a spinal cord. During impact, dynamic
measurements were made with use of transducers to measure pressure in a
synthetic spinal cord material, and a high-speed video camera filmed the
inside of the spinal canal. A corresponding finite element model was created
to determine the effect of the spinal cord on the dynamics of the bone
Results: The high-speed video clearly showed the fragments of bone
being projected from the vertebral body into the spinal canal before being
recoiled, by the action of the posterior longitudinal ligament and
intervertebral disc attachments, to their final resting position. The pressure
measurements in the synthetic spinal cord showed a peak in canal pressure
during impact. There was poor concordance between the extent of postimpact
occlusion of the canal as seen on the computed tomography images and the
maximum amount of occlusion that occurred at the moment of impact. The finite
element model showed that the presence of the cord would reduce the maximum
dynamic level of canal occlusion at high fragment velocities. The cord would
also provide an additional mechanism by which the fragment would be recoiled
back toward the vertebral body.
Conclusions: A burst fracture is a dynamic event, with the maximum
canal occlusion and maximum cord compression occurring at the moment of
impact. These transient occurrences are poorly related to the final level of
occlusion as demonstrated on computed tomography scans.
Clinical Relevance: In a thoracolumbar burst fracture, the final
position of the fragments, as seen on computed tomography images at
presentation, probably does not represent the maximum level of canal occlusion
or peak cord pressure and therefore does not represent the probable damage to
the cord tissue that occurred at the moment of impact.