Impact of Screw Insertion Technique on Thoracic Pedicle Screw Anchorage: Biomechanical Comparison of the Modified Slide, Slide, Funnel, and Conventional Techniques.

Abstract

Background: Several techniques have been developed to facilitate safe and accurate thoracic pedicle screw placement. However, their impact on screw anchorage has not been systematically evaluated. This study compared thoracic pedicle screw anchorage following placement using the Modified Slide, Slide, Funnel, and Conventional techniques under cyclic loading.

Study design: Cadaveric biomechanical study.

Methods: Forty-five fresh-frozen human thoracic vertebrae (T4-T11) were allocated to three experimental groups (n = 15 each). For standardized paired comparisons, one randomly selected pedicle of each vertebra was instrumented using the Modified Slide technique, developed by the authors as a refinement of the original Slide technique, and the contralateral pedicle with one of three established techniques. Screws were subjected to cyclic craniocaudal loading until loosening or a maximum load level of 750 N.

Results: Screws placed using the Modified Slide technique withstood 1.9-fold and 1.5-fold more load cycles until loosening than those placed with the Slide and Funnel techniques, respectively (both p < 0.001), but only 0.9-fold that of screws inserted with the Conventional technique (p = 0.008).

Conclusions: The Modified Slide technique preserves the advantage of the Funnel and original Slide techniques by allowing direct visualization of the pedicle entry point for accurate screw placement, yet substantially enhances thoracic pedicle screw anchorage compared with those techniques. Although anchorage was lower than that of the Conventional technique, screws placed using the Modified Slide technique still withstood loads substantially exceeding those reported to occur during daily activities.