Biomechanical Stability of Transverse Connectors in the Setting of a Thoracic Pedicle Subtraction Osteotomy

Abstract

Introduction The biomechanical effect of augmentation of a longitudinal constructs with one or two transverse connectors (TC) after a thoracic pedicle subtraction osteotomy (PSO) has not been evaluated previously. Previous investigations have suggested the role of transverse connectors for long segment thoracic constructs in enhancing torsional rigidity. We set out to evaluate the biomechanical contribution of TC to the stability of a long-segment pedicle screw–rod construct after a thoracic PSO. Methods Seven human cadaveric thoracic spines were prepared and instrumented from T4 to T10 with bilateral pedicle screws/rods and a PSO was performed at T7. Intact range of motion (ROM) testing was performed with nondestructive loading and analyzed by loading modality (axial rotation, flexion/extension, and lateral bending). ROM analysis was performed in the unaugmented construct, the construct augmented with one TC, and the construct augmented with two TC. No outside funding sources were utilized for this study. The authors have no potential conflicts of interest to report. Results Following PSO and an unaugmented longitudinal pedicle screw–rod construct, T4–T10 (overall construct) and T6–T8 (PSO site). ROM was significantly reduced in all planes of motion compared with intact condition ( p < 0.05). Augmentation of longitudinal construct with either one or two TC did not significantly increase construct stability in flexion-extension or lateral bending compared with the unaugmented construct ( p > 0.05). In contrast, during axial rotation, global ROM was significantly reduced by 43% and by 48% at T6–T8 following addition of two TC ( p < 0.05). One TC did not significantly reduce torsional ROM. Conclusions Two transverse connectors significantly improved torsional rigidity of the entire construct and at the PSO site, with no differences in stability for flexion-extension and lateral bending, or with the addition of only one transverse connector. In the setting of a PSO and long segment pedicle screw–rod construct, augmentation with at least two transverse connectors should be considered to improve torsional rigidity.