Comparing the Biomechanical Stability of Cortical Screw Trajectory Versus Standard Pedicle Screw Trajectory for Short- and Long-Segment Posterior Fixation in 3-Column Thoracic Spinal Injury.

Background: Information on the performance of posterior fixation with cortical screw (CS) versus pedicle screw (PS) trajectories for stabilizing thoracolumbar burst fractures is limited. Therefore, we sought to analyze stability with CS versus PS in short- and long-segment fixations using a 3-column spinal injury model.

Methods: Nondestructive flexibility tests: (1) intact, (2) intact + short fixation, (3) intact + long fixation, (4) after burst fracture, (5) short fixation + burst fracture, and (6) long fixation + burst fracture using thoracic spine segments (7 CS, 7 PS).

Results: With CS, the range of motion (ROM) was significantly greater with short-segment than with long-segment fixation in all directions, with and without burst fracture ( ≤ .008). With PS and burst fracture, ROM was significantly greater with short fixation during lateral bending and axial rotation ( < .006), but not during flexion-extension ( = .10). Groups with CS versus PS were not significantly different after burst fracture during flexion-extension and axial rotation, with short ( ≥ .58) or long fixation ( ≥ .17). During lateral bending, ROM was significantly greater with CS versus PS, without burst fracture (long fixation,  = .02) and with burst fracture (short and long fixation,  ≤ .001).

Conclusions: CS trajectory is a valid alternative to PS trajectory for thoracic spine fixation in 3-column spinal injuries, and long-segment fixation is superior to short-segment fixation with either.