Biomechanical comparison of pull-out strength of different cementation and pedicle screw placement techniques in a calf spine model

Abstract

Background: we hypothesized that an entire pedicle screw tract cement augmentation has greater strength than traditional techniques. Method: twenty-four fresh frozen calf lumbar spines were randomized into three study groups, each having eight vertebrae: (1) screw cemented after vertebroplasty; (2) fenestrated cemented screw; and (3) cementation of the entire pedicle screw tract. For the right side screws, two pedicle screws were inserted in each vertebra with the standard position in the sagittal plane, whereas the left side screws were placed at a 30 degrees angle craniocaudal plane. From the recorded force-displacement curves, the maximum peak load (failure load) of each screw was determined. The mode of failure was screw stripping at all levels tested. Results: the pull-out strength for standard screw replacement at the sagittal plane was 1843.3 N, 1707.45 N, and 5365.1 N consecutively. The failure load value in the standard position in the sagittal plane in the cementation of the entire pedicle screw tract group was significantly higher than that in the fenestrated cemented screw group and screw cemented after vertebroplasty (p < 0.001 andp < 0.001, respectively). The standard pedicle screw position in the sagittal plane showed a significant pull-out strength than the others (p < 0.001). Conclusion: the pull-out strength of the cementation of the entire pedicle screw tract was 2.5 times higher than the others. The pull-out strength of the pedicle screws in malposition obtained the same strength to the standard positions after the augmentation procedure in our study.