Eric O. Klineberg, Mark Kayanja, Dhruv B. Pateder and Isador Lieberman
Introduction: The L5-S1 trans-sacral axial rod represents a less invasive approach to spinal fixation. No study to date has biomechanically tested this device to failure to compare it to the more common pedicle screw instrumentation in the human cadaveric spine.
Methods: Seven human lumbar spines (L4-pelvis) with an average t score of -3.5, were randomly divided into a pedicle screw construct [4] and axial trans-sacral rod [3]. The spines were then tested in a custom built platform to determine the effect of a pure flexion moment. Testing was performed with six cycles (10 N/m), and final destructive testing (maximum 50 N/m).
Results:The pedicle screw construct has similar motion at the L5/S1 junction compared to the trans-sacral rod construct in cyclical testing. With destructive testing, no significant motion difference is observed at the L5/S1 segment, and no overt failure was noted. However, there was free motion and displacement at the L4/5 segment and in 3 specimens there was complete failure of the posterior ligamentous complex.
Conclusion: The trans-sacral axial rod was comparable to pedicle screws at the L5/S1 disc space in a pure flexion biomechanical model. No overt failure was observed in the destructive testing at the instrumented levels
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