Pedicle Screw Configuration for Thoracolumbar Burst Fracture Treatment: Short versus Long Posterior Fixation Constructs with and without Anterior Column Augmentation

STUDY DESIGN: An in-vitro study. PURPOSE: The current study is aimed at investigating the differences in stability between short posterior fixation (SPF), hybrid posterior fixation (HPF), and long posterior fixation (LPF) with and without anterior column augmentation using calcium phosphate bone cement (CaP) for treating burst fractures (BFs). OVERVIEW OF LITERATURE: The ideal treatment for thoracolumbar BF is controversial regarding the use of short or LPF constructs. METHODS: Seven human thoracolumbar spines (T9-L4) were tested on a six degree of freedom spine simulator in three physiologic planes, flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Tested surgical constructs included the following: intact, injury (BF), SPF (T12-L2), HPF (T11-L2), LPF (T11-L3), SPF+CaP, HPF+CaP, LPF+CaP, and CaP alone (CaP). Range of motion (ROM) was recorded at T12-L2 in FE, LB, and AR. RESULTS: The reduction in mean ROM trended as follows: LPF>HPF>SPF. Only LPF constructs and HPF with anterior column augmentation significantly reduced mean ROM in FE and LB compared to the intact state. All instrumented constructs (SPF, HPF, and LPF) significantly reduced ROM in FE and LB compared to the injured condition. Furthermore, the instrumented constructs did not provide significant rotational stability. Injecting CaP provided minimal additional stability. CONCLUSIONS: For the injury created, LPF and HPF provided better stability than SPF with and without anterior column augmentation. Therefore, highly unstable fractures may require extended, long or hybrid fusion constructs for optimum stability.

Biomechanical Evaluation of a Novel Posterior Integrated Clamp That Attaches to an Existing Posterior Instrumentation for Use in Thoracolumbar Revision

STUDY DESIGN: An in vitro biomechanical study. PURPOSE: To evaluate the biomechanics of a novel posterior integrated clamp (IC) that extends on an already implanted construct in comparison to single long continuous bilateral pedicle screw (BPS) and rod stabilization system. OVERVIEW OF LITERATURE: Revision surgery in the thoracolumbar spine often necessitates further instrumentation following a failed previous back surgery. Stability of these reconstructed constructs is not known. METHODS: Six osteoligamentous T12-L5 calf spines were tested on a spine motion simulator in the following configurations: intact, four level constructs (T13-L4), three level constructs (L1-L4), and two level constructs (L2-L4), by varying the ratio between BPS and IC. A load control protocol of 8 Nm moments was applied at a rate of 1degrees/sec to establish the range of motion value for each construct in flexion-extension, lateral bending, and axial rotation. Statistical analysis was performed on raw data using repeated measures analysis of variance and significance was set at p<0.05. RESULTS: On an average, the reduction in motion for the four level continuous pedicle screw and rod construct (67%) was similar to those extended with integrated clamps (64%). Furthermore, for three level and two level constructs, no significant difference was observed between continuous pedicle screw constructs and those revised with the integrated clamps (regardless of the ratio between BPS and IC). CONCLUSIONS: The novel posterior IC showed equivalent biomechanical rigidity to continuous pedicle screw rod constructs in revision scenarios. Clinical studies on posterior rod adjunct systems are necessary to confirm these results.