Biomechanical Evaluation of a Bilateral, Dual-Rod Fixation Construct in the Thoracolumbar Spine: A Cadaveric Analysis

Abstract

Posterior pedicle screw and rod fixation has become standard in the treatment of oncological resections requiring stabilization, deformity correction and unstable thoracolumbar fractures. Given the high mechanical stress at the points of highest instability, some clinicians have utilized dual rods on each side to augment the construct. The added advantage of this type of construct has not been previously evaluated in-vitro. The goal of this study is to evaluate the biomechanical advantage of a dual rod construct in the thoracolumbar spine, using a burst fracture cadaveric model. Methods: Seven fresh human cadaveric (T9-L3) spines were tested in normal conditions, after an iatrogenic T12 burst fracture, and successively after laminectomy and standard two rod pedicle screw stabilization (two level above and two below) and two different dual rod overlapping constructs. Pure moment torque was applied quasistatically, while 3D motion was measured optoelectronically. Thoracolumbar range of motion was measured during flexion, extension, left / right lateral bending, and left / right axial rotation. Results: All constructs significantly stabilized the simulated burst fracture in all modes of testing. There was no statistically significant difference, however, in the ability to restrict motion between the 3 different constructs, either from T10-L2, or across the fracture segment of T11-L1. Conclusions: There does not appear to be a biomechanical advantage to using dual rods over standard single rods for immediate fixation in an unstable segment. Whether dual rods protect the construct against long-term failure is not yet known.