The role of the anterior longitudinal ligament in Harrington rod fixation of unstable thoracolumbar spinal fractures.

This study was carried out to identify the role of the anterior longitudinal ligament in Harrington distraction rod fixation of the unstable spine, and to suggest clinical means of detecting a ruptured ligament when this is not obvious from a preoperative radiogram. In the unstable thoracolumbar spine, a marked difference in force is required for distraction and stabilization when the ligament is intact compared with when the ligament is disrupted. This can be detected by using a force-indicating distractor during the procedure. Furthermore, when the anterior longitudinal ligament is disrupted, the pattern of vertebral movements during distraction is altered. With the ligament intact, the vertebrae adjacent to the unstable segment will angulate around an axis situated ventral to the vertebral bodies, while the vertebrae will move apart in parallel planes when the ligament is severed. This can easily be detected by studying the movements of Kirschner wires inserted into the spinous processess.