Investigator: Scott A. Yerby, PhD Project Staff: Jen Kreshak, BS; Daniel Kim, MD; A. Kam, MD; and M. Panjabi, PhD Project Categories: Spinal Cord Injury / Osteoporosis - 2000 Relative to other parts of the spine, little is reported about fixation at the cervicothoracic junction and few studies have addressed fixation stability at this location, even though injuries at this location have been reported as high as 9% of cervical spine injuries. The objective of this study was to biomechanically test three frequently used posterior cervical fixations devices on human cadaveric specimens and evaluate them for stability with a posterior two-column and three-column injury at the cervicothoracic junction. This work is intended to help researchers and clinicians better understand the biomechanics of the cervicothoracic junction. Eighteen human cadaver spines (C3-T3) were tested in flexion/extension, lateral bending, and axial rotation to 2.5 Nm in each direction. Specimens were tested in the following configurations: intact, posterior instrumentation with a posterior two-column injury, and posterior instrumentation with a three-column injury. One of three posterior instrumentation systems was used for each specimen: the Synthes Cervifix and DePuy Summit systems, both posterior rod and screw systems, and the Danek Axis system, a posterior plate and screw system. With all fixation systems, lateral mass screws were placed at C5 and C6 and pedicle screws were placed at T1 and T2. The mean stiffness, range of motion (ROM), and neutral zone (NZ) during flexion/extension, left and right lateral bending, and left and right axial torsion were compared between intact specimens and the instrumented specimens with two- and three-column injuries using a one-way blocked analysis of variance with a statistical significance of 0.05. Differences between individual means were compared using a Bonferroni follow-up test. All three systems adequately stabilized the two-column injury in flexion/extension, lateral bending, and axial rotation, but failed to stabilize the three-column injury in extension. These results suggest that all three systems adequately stabilize the cervicothoracic junction with a posterior two-column injury in flexion, extension, lateral bending and axial rotation. All systems, however, failed to provide adequate stability in extension for a three-column injury at this level. A three-column injury at this level would warrant posterior fixation and supplemental anterior fixation since the transected ALL and anterior disc no longer provide resistance in extension. This study provides researchers and clinicians insight into the ability of posterior stabilization to stabilize a two-column injury and the inability to stabilize a three-column injury at the cervicothoracic junction. Funding Source: Stanford University (Department of Neurosurgery) and North American Spine Society |
