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

Lateral view radiograph shows the modeled burst fracture at T9. Anterior (O) and posterior (X) anatomic landmarks were used for tracking during motion analysis and for calculations of vertical displacement during compressive loading. Bone at the superior one-third of the vertebral body, including the posterior cortex and proceeding laterally to the pedicles, was removed using a high-speed drill. The posterior longitudinal ligament was kept intact. Used with permission from Barrow Neurological Institute, Phoenix, Arizona.

Test configurations for pure moment (A) angular flexibility loading and (B) compression loading performed in a standard servo-hydraulic test frame (MTS Systems Corp., Eden Prairie, Minnesota). During flexibility tests, adjustable pulleys were used, enabling 2 equal and opposite forces separated by a small distance (pure moment) to be applied via a loop of string when the piston advanced upward. Optical markers for tracking specimen motion are also visible. Shown for (A) left lateral bending; reconfiguring the string and pulleys allows for flexion, extension, or axial rotation. The angle vise securing (B) the construct was repositioned on the base of the test frame in the transverse plane until minimal intervertebral rotations were observed during application of the compressive load via the piston (arrow). Shown for short-segment fixation with cortical screws and rods (distal and proximal screws in place but not attached to rods, posterior view). Used with permission from Barrow Neurological Institute, Phoenix, Arizona.

Mean range of motion across T8-T10 (or T7-T9) for all conditions (intact vertebrae, FX with short-segment and long-segment fixation, and FX before fixation). (A) Flexion-extension, (B) lateral bending, and (C) axial rotation. P values are based on statistical analysis of raw values of range of motion. Error bars indicate SD. Abbreviations: CS, cortical screw; FX, burst fracture; PS, pedicle screw. Used with permission from Barrow Neurological Institute, Phoenix, Arizona.