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A biomechanical comparison of crossed and parallel rod configurations in atlantoaxial internal fixation

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Abstract

Background

Posterior atlantoaxial fixation with screw rod forms an approximate “II” shape or “H” increasing transverse link for better stability. In order to improve stability and in consideration of difficult placement of transverse connecting rod, possibility of inadequate bone graft, some scholars have preliminarily researched biomechanics of a novel crossed rod as an approximate “X” configuration of screw rod.

Purpose

The aim of this study was to evaluate and compare the biomechanics of the crossed and parallel rod configurations in the screw rod system for posterior atlantoaxial fixation on a cadaveric model.

Methods

Six fresh cervical specimens were used to complete the range of motion (ROM) testing by applying pure moments of ± 2.0 nm. Following intact state and under destabilization testing, screws were implanted. The specimens were then tested in the following sequence: Group BLS + PR (C2 bilateral laminar screws + parallel rod), Group BLS + CR (C2 bilateral laminar screws + crossed rod), LPRLS + PR (C2 left pedicle screw and right laminar screw + parallel rod), LPRLS + CR (C2 left pedicle screw and right laminar screw + crossed rod), BPS + PR (C2 bilateral pedicle screws + parallel rod) and BPS + CR (C2 bilateral pedicle screws + crossed rod). The ROM of the C1–2 segments was measured in flexion–extension, lateral bending and axial rotation. Six surgical constructs were compared between the groups and with intact condition, respectively.

Results

The six fixed modes significantly increased stability compared with both the intact and destabilization group in flexion–extension, lateral bending and axial rotation (p < .05). In extension, BPS + CR and BLS + CR showed greater stability than BLS + PR (p < .05). During flexion, the six fixation methods showed no statistical significance (p > .05). In left lateral bending, stability of the other five screw rod fixation techniques significantly increased when compared with BLS + PR (p < .05). In the right lateral bending direction, the stability of BLS + PR was worse than that of BPS + CR and BPS + PR (p < .05). In the left axial rotation, stability of BLS + CR, LPRLS + CR and BPS + CR was greater than that of BLS + PR, LPRLS + PR and BPS + PR (p < .05). In the right axial rotation, the stability of BPS + CR and BLS + CR was greater than that of BLS + PR (p < .05).

Conclusion

The six investigated fixation methods provide sufficient biomechanical stability. The crossed rod configuration can further enhance the axial rotation stability of the screw rod system, which consists of C1 bilateral pedicle and C2 pedicle, or C2 lamina screws. The crossed rod can also improve the stability of the screw rod system made up of C1 bilateral pedicle and C2 lamina screws in lateral bending and extension. The crossed rod configuration is reliable and provides superior stability for clinical application.

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Acknowledgments

Funding was received in support of this work from the Science and technology project of Guangdong Province (grant number 201803010046) and Science and technology project of Guangdong Province (grant number 2015B020233013).

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Author notes

  1. Both are the first authors Feng Qiu, Xiao-Bao Zhou make equal contribution to this work.

Authors and Affiliations

  1. Department of Orthopaedic, Puning Overseas Chinese Hospital, 515300, Puning, Jieyang, Guangdong, People’s Republic of China

    Feng Qiu, Xi-Lin Xu, Wei-Cheng Jiang & Geng-Chao Liu

  2. The First School of Clinical Medicine, Southern Medical University, No.1838 North of Guangzhou Road, 510515, Guangzhou, People’s Republic of China

    Xiao-Bao Zou

  3. Department of Orthopedics, General Hospital of Southern Theatre Command of PLA, 111 Liuhua Road, 510010, Guangzhou, People’s Republic of China

    Xiang-Yang Ma

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  1. Feng Qiu
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Correspondence to Xiang-Yang Ma.

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Qiu, F., Zou, XB., Xu, XL. et al. A biomechanical comparison of crossed and parallel rod configurations in atlantoaxial internal fixation. Eur Spine J 30, 576–584 (2021). https://doi.org/10.1007/s00586-020-06655-6

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