Posterior stabilization at the cervicothoracic junction - A biomechanical study

Study Design. This study biomechanically evaluated three fixation devices for stability with posterior two- and three-column injuries. Objectives. To find an effective means of posteriorly stabilizing injuries at the cervicothoracic junction. Summary of Background Data. The cervicothoracic spine is complex anatomically and has been a difficult challenge in approach and stabilization of traumatic and degenerative disorders. Methods. Twenty-one human cadaveric spines (C3-T3) were loaded in flexion, extension, lateral bending, and axial torsion. A posterior two-column injury was created at C7-T1. One of three posterior fixation systems was applied (two rod-screw systems, one plate-screw system, all with screws at C5, C6 and T1, T2). The spines were tested again. A three-column injury was created by transecting the remaining anterior structures; the spines were tested a final time. Results. In flexion-extension, there were no significant differences in stiffness between intact and instrumented two-column injury specimens for all systems; the instrumented three-column injury was significantly (P < 0.05) less stiff than intact specimens in extension. Ranges of motion and neutral zones decreased from intact to instrumented two-column injuries and increased from intact to three-column constructs. In lateral bending and axial rotation, all systems were stiffer than intact spines for both injuries; ranges of motion and neutral zones were reduced for both injuries compared with intact specimens. Conclusion. All three systems stabilize the cervicothoracic junction with a posterior two-column injury in flexion-extension, lateral bending, and axial rotation; none was adequate for a three-column injury, particularly in extension. A three-column injury at this level would warrant supplemental anterior fixation.