The Trans-Spinous Crosslink Increases the Pull-Out Strength of the Pedicle Screw Instrumentation

To evaluate whether adding an extra anchoring point to the construct by passing the crosslink through a hole in the spinous process (trans-spinous crosslink technique), may prevent screw loosening by increasing the pull-out strength.

Twenty-four fresh-frozen single lumbar sheep vertebrae were instrumented with pedicle screws bilaterally, and they are connected to each other with a crosslink. All vertebrae were assigned randomly to either the experiment (trans-spinous crosslink) group or the control group. In the experiment group, the crosslink was passed through a hole within the spinous process. In the control group, the posterior part of the hole was removed. The pull-out force of the construct was determined using a mechanical testing machine.

The mean pull-out forces of the experiment group and the control group were 1949 ± 361.55 N and 1338.57 ± 220.26 N, respectively. The pull-out force of the experiment group was significantly higher than those of the control group with 99.9% confidence (p < 0.001).

The pedicle screws rigidly anchor the internal fixation devices to the vertebral colon. In classical construct design, pedicle screws share the load. Adding extra anchoring points decreases screw share and may prevent construct pull-out. This study shows that the trans-spinous crosslink can serve as an anchoring point and increases the construct pull-out strength.