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. 2020 Jul 13;21(1):460.
doi: 10.1186/s12891-020-03498-6.

Influence of cement-augmented pedicle screws with different volumes of polymethylmethacrylate in osteoporotic lumbar vertebrae over the adjacent segments: a 3D finite element analysis

Hui-Zhi Guo  1   2 , Shun-Cong Zhang  1   2 , Dan-Qing Guo  1 , Yan-Huai Ma  1   2 , Kai Yuan  2 , Yong-Xian Li  1   2 , Jian-Cheng Peng  1   2 , Jing-Lan Li  1 , De Liang  2 , Yong-Chao Tang  3
Affiliations

Influence of cement-augmented pedicle screws with different volumes of polymethylmethacrylate in osteoporotic lumbar vertebrae over the adjacent segments: a 3D finite element analysis

Hui-Zhi Guo et al. BMC Musculoskelet Disord. .

Abstract

Background: Polymethylmethacrylate (PMMA) is commonly used for cement-augmented pedicle screw instrumentation (CAPSI) to improve the fixation stability and reduce the risk of screw loosening in the osteoporotic thoracolumbar spine. Biomechanical researches have shown that various dose of cement (1-3 ml) can be injected to enhance screw stability. To date, there have been no studies on the relationship between adjacent segment degeneration and the volume of PMMA. This study aimed to explore the influence of CAPSI with different volumes of PMMA in osteoporotic lumbar vertebrae over adjacent segments by using finite element analysis.

Methods: Seven different finite element models were reconstructed and simulated under different loading conditions, including (1) an intact model, (2) three single-level CAPSI models with different volumes of PMMA (1, 1.73, and 2.5 ml), and (3) three double-level CAPSI models with different volumes of PMMA (1, 1.73, and 2.5 ml). To improve the accuracy of the finite element analysis, the models of the injectable pedicle screw and bone cement were created by using a three-dimensional scanning machine and the CAPSI patient's CT data, respectively. The range of motion (ROM), the stress of intervertebral discs, and the stress of facet in the adjacent segment were comparatively analyzed among the different models.

Results: The ROMs of the different segments were compared with experimental data, with good agreement under the different load conditions (21.3°, 13.55°, 13.99°, and 6.11° in flexion, extension, bending, and rotation at L3-S1 level, respectively). Compared with the intact model, the ROM, disc stresses, and facet stress in adjacent segments were found to be higher in the six operative models. Otherwise, with a larger volume of PMMA injected, the ROM, disc stresses, and facet stress slightly increased at the adjacent segment. However, the differences were insignificant with the biggest difference less than 3.8%.

Conclusions: CAPSI could increase the incidence of disk degeneration in the adjacent segment, while within a certain range, different volumes of PMMA provided an approximate impact over the adjacent segment degeneration.

Keywords: Adjacent segment degeneration; Cement-augmented pedicle screws; Finite element analysis; Polymethylmethacrylate.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
a The fenestrated pedicle screw material and picture of the 3D scanner working; b the model of the fenestrated pedicle screw
Fig. 2
Fig. 2
The models of CAPSI following single-level lumbar interbody fusion (a)1.0 ml PMMA per screw; b 1.73 ml PMMA per screw; c 2.5 ml PMMA per screw
Fig. 3
Fig. 3
The models of CAPSI following double-level lumbar interbody fusion (a)1.0 ml PMMA per screw; b 1.73 ml PMMA per screw; c 2.5 ml PMMA per screw
Fig. 4
Fig. 4
The ROM of adjacent segments following single (a) and double-level (b) lumbar spinal fusion
Fig. 5
Fig. 5
The disc stress of adjacent segments following single (a) and double-level (b) lumbar spinal fusion
Fig. 6
Fig. 6
The peak von Mises stress distribution of L3–4 disc in double-level CAPSI model with different volumes of PMMA
Fig. 7
Fig. 7
The facet stress of adjacent segments following single (a) and double-level (b) lumbar spinal fusion
See this image and copyright information in PMC

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