Thoracic pedicle screw anchorage using the new modified slide technique

Abstract-Text (inkl. Referenzen und Bildunterschriften)

Background: Pedicle screws have earned high acceptance in a broad variety of spinal surgeries. Nevertheless, placement in the thoracic spine remains a challenge due to the difficult anatomical conditions, particularly if deformities are present. Several freehand insertion techniques have been described to identify the pedicle entry point and to minimize the risk of screw misplacement. However, some techniques might compromise pedicle screw anchorage, while allowing safe screw placement.

Aims: This study investigated pedicle screw anchorage of screws placed with the new "Modified Slide"-technique (MS) and compared it to the Slide-technique by Vialle et al. and the conventional technique.

Material and Methods: Thirty fresh frozen human thoracic vertebrae (Th4–Th11; mean age: 68 ± 15.6; mean BMD: 99.2 mg/ccm ± 23.8) were used in this study. For pairwise comparisons, one randomly selected pedicle of each vertebra was instrumented using the new MS-technique. The contralateral side was instrumented using either the Slide-technique or the conventional technique. Each screw was tested using cyclic cranio-caudal loading with an initial load ranging from -50N to +50N with stepwise increasing compressive load (5N every 100 cycles) until screw loosening. After loosening was detected, a pull-out test was performed.

Results: Screws implanted using the MS-technique sustained significantly higher loads than those using the Slide-technique (460 N ±160.4vs. 253 N ± 95.2 ; p < 0.01) but lower loads than screws conventionally implanted (442 N ± 94 vs. 546 N ± 177.4; p < 0.01). Pullout tests did not differ between groups (p = 0.19), (p = 0.52).

Conclusion: In terms of screw anchoring, the MS-technique is in between the conventional and the Slide-technique. It can sustain higher loads than those measured in daily activities while still allowing safe screw implantation. Therefore the "Modified Slide"-technique could be a helpful assistance technique for safe pedicle screw placement.