Thoracolumbar burst fracture: evaluating stability.

The burst fracture is an injury characterized by anterior vertebral body height loss and retropulsion of the posterior aspect of the vertebral body into the spinal canal. The vertebral body injury frequently is associated with fractures through the neural arch. Using a three-column concept of spinal stability, the division of these fractures into stable and unstable injuries is difficult. Radiographic signs of instability include widening of the interspinous and interlaminar distance, translation of more than 2mm, kyphosis of more than 20 degrees, dislocation, height loss of more than 50%, and articular process fractures. However, fractures may be unstable in the absence of these signs. Unrecognized supraspinous ligament disruption contributes to this instability. This structure is best evaluated by MR examination. Confirmation of posterior ligamentous disruption occurring in conjunction with the burst fracture leads to reevaluation of the presumed mechanism of injury. This article discusses the many issues surrounding the division of burst fractures into stable and unstable injuries and reexamines the common classification systems of thoracolumbar spine injuries.