Screw malposition, such as lateral wall breach or end-plate breach, is one of the main pitfalls of inserting pedicle screws.
Methods: From 17 fresh spines 54 vertebrae were harvested. In each vertebra on one pedicle the screw was inserted correctly down the axis of the pedicle, while on the other pedicle the screw was inserted to breach the lateral wall or the end-plate. The 18 pedicle screws that breached the lateral wall were then removed and re-directed along the correct axis of the pedicle. The 18 pedicle screws that breached the end-plate were removed and re-directed along the correct axis of the pedicle. The 18 other pedicle screws that had breached the end-plate were not removed. The pullout force of pedicle screws was measured.
Results: 1) The mean pullout strength for the re-directed screws following lateral wall breach was 24.0% less as compared to the correctly aligned screws; 2) The mean pullout strength for the re-directed screws following end-plate breach was 23.3% less as compared to the correctly aligned screws; 3) The mean pullout strength for the pedicle screws end-plate breach was 7.6% less as compared to the correctly aligned screws.
Conclusion: The pullout strength of re-directed pedicle screws after either a lateral pedicle breach or end-plate breach is significantly less than the pullout strength of correctly aligned screw. A pedicle screw that is not re-directed after end-plate breach is weaker than a pedicle screw correctly aligned, however the difference is not significant
