Is a cross-connector beneficial for single level traditional or cortical bone trajectory pedicle screw instrumentation?

Frédéric Cornaz,Keitaro Matsukawa,José Miguel Spirig,Jess Gerrit Snedeker,Marie-Rosa Fasser,Jonas Widmer,Mazda Farshad,Alejandro A Espinoza Orías

doi:10.1371/journal.pone.0253076

Abstract

The cortical bone trajectory (CBT) has been introduced with the aim of better screw hold, however, screw-rod constructs with this trajectory might provide less rigidity in lateral bending (LB) and axial rotation (AR) compared to the constructs with the traditional trajectory (TT). Therefore, the addition of a horizontal cross-connector could be beneficial in counteracting this possible inferiority. The aim of this study was to compare the primary rigidity of TT with CBT screw-rod constructs and to quantify the effect of cross-connector-augmentation in both. Spines of four human cadavers (T9 –L5) were cropped into 15 functional spine units (FSU). Eight FSUs were instrumented with TT and seven FSUs with CBT pedicle screws. The segments were tested in six loading directions in three configurations: uninstrumented, instrumented with and without cross-connector. The motion between the cranial and caudal vertebra was recorded. The range of motion (ROM) between the CBT and the TT group did not differ significantly in either configuration. Cross-connector -augmentation did reduce the ROM in AR (16.3%, 0.27°, p = 0.02), LB (2.9%, 0.07°, p = 0.03) and flexion-extension FE (2.3%, 0.04°, p = 0.02) for the TT group and in AR (20.6%, 0.31°, p = 0.01) for the CBT-group. The primary rigidity of TT and CBT single level screw-rod constructs did not show significant difference. The minimal reduction of ROM due to cross-connector-augmentation seems clinically not relevant. Based on the findings of these study there is no increased necessity to use a cross-connector in a CBT-construct.

Highlights

Dorsal pedicle screw instrumentation of the spine is an effective method to attain primary stability required for bony fusion
While some limited evidence can be found for the beneficial effect of CC on TT-constructs [7,8,9,10,11,12], none is available for cortical bone trajectory (CBT) constructs. These considerations lead to three hypotheses: 1) CBT-constructs are less stable in axial rotation (AR), lateral bending (LB) and lateral shear (LS), 2) CBT constructs are more stable in FE and 3) CC-augmentation is more effective in CBT-constructs compared to TT-constructs
There are certain indications of inferior stability in AR and LB and superior stability FE for CBT-constructs [5, 6]. These observations lead to hypotheses 1) CBT-constructs are less stable in AR, LB and LS and 2) CBT constructs are more stable in FE

Summary

Introduction

Dorsal pedicle screw instrumentation of the spine is an effective method to attain primary stability required for bony fusion. More rigid instrumentations lead to higher fusion rates [1] and instrumentations for fusion are optimized to provide high stiffness in all loading directions. Pedicle screws used for this purpose are mostly implanted in the traditional. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. There are no other competing interests in relation to the content of this manuscript. This does not alter our adherence to PLOS ONE policies on sharing data and materials

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