Effects of Revision Rod Position on Spinal Construct Stability in Lumbar Revision Surgery: A Finite Element Study

January 25, 2022

doi: 10.3389/fbioe.2021.799727.

eCollection 2021.

Affiliations

¹ Department of Orthopaedics, Xijing Hospital, The Air Force Medical University, Xi’an, China.
² Department of Orthopaedics, Air Force Hospital of Eastern Theater Command, Nanjing, China.
³ Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, China.
⁴ National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, Tianjin University of Technology, Tianjin, China.

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Quan-Chang Tan et al.

Front Bioeng Biotechnol.

2022.

doi: 10.3389/fbioe.2021.799727.

eCollection 2021.

Affiliations

¹ Department of Orthopaedics, Xijing Hospital, The Air Force Medical University, Xi’an, China.
² Department of Orthopaedics, Air Force Hospital of Eastern Theater Command, Nanjing, China.
³ Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, China.
⁴ National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, Tianjin University of Technology, Tianjin, China.

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Abstract

Revision surgery (RS) is a necessary surgical intervention in clinical practice to treat spinal instrumentation-related symptomatic complications. Three constructs with different configurations have been applied in RS. One distinguishing characteristic of these configurations is that the revision rods connecting previous segments and revision segments are placed alongside, outside, or inside the previous rods at the level of facetectomy. Whether the position of the revision rod could generate mechanical disparities in revision constructs is unknown. The objective of this study was to assess the influence of the revision rod position on the construct after RS. A validated spinal finite element (FE) model was developed to simulate RS after previous instrumented fusion using a modified dual-rod construct (DRCm), satellite-rod construct (SRC), and cortical bone trajectory construct (CBTC). Thereafter, maximum von Mises stress (VMS) on the annulus fibrosus and cages and the ligament force of the interspinous ligament, supraspinous ligament, and ligamentum flavum under a pure moment load and a follower load in six directions were applied to assess the influence of the revision rod position on the revision construct. An approximately identical overall reducing tendency of VMS was observed among the three constructs. The changing tendency of the maximum VMS on the cages placed at L4-L5 was nearly equal among the three constructs. However, the changing tendency of the maximum VMS on the cage placed at L2-L3 was notable, especially in the CBTC under right bending and left axial rotation. The overall changing tendency of the ligament force in the DRCm, SRC, and CBTC was also approximately equal, while the ligament force of the CBTC was found to be significantly greater than that of the DRCm and SRC at L1-L2. The results indicated that the stiffness associated with the CBTC might be lower than that associated with the DRCm and SRC in RS. The results of the present study indicated that the DRCm, SRC, and CBTC could provide sufficient stabilization in RS. The CBTC was a less rigid construct. Rather than the revision rod position, the method of constructing spinal instrumentation played a role in influencing the biomechanics of revision.

Keywords:

biomechanics; construct configuration; cortical bone trajectory; dual-rod; finite element analysis; satellite rod.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

**FIGURE 1**

Schematic posterior-anterior illustration of revision models with revision rods placed alongside **(DRCm, A)**, outside **(SRC, B)**, and inside **(CBTC, C)** the previous rods.

**FIGURE 2**

Lateral views of the RS FE model constructed using the DRCm **(A)**, SRC **(B)**, and CBTC **(C)**.

**FIGURE 3**

Maximum VMS was distributed on the annulus fibrosus after RS was instrumented using the DRCm, SRC, and CBTC in the loading direction of FL, EX, LB, LAR, and RAR.

**FIGURE 4**

Distribution characteristics of the maximum VMS on the cage at the revision level after RS **(A)** and its tendency for change among the three constructs **(B)**.

**FIGURE 5**

Distribution characteristics of the maximum VMS on the cage at the previous surgical level **(A)** and its tendency for change among the three constructs **(B)**.

**FIGURE 6**

Ligament force of the ISL in the loading direction of FL, LB, RB, LAR, and RAR after RS instrumentation using the DRCm, SRC, and CBTC.

**FIGURE 7**

Ligament force of the SSL in the loading direction of FL, LB, RB, LAR, and RAR after RS instrumentation using the DRCm, SRC, and CBTC.

**FIGURE 8**

Ligament force of FL in the loading direction of FL, LB, RB, LAR, and RAR after RS instrumentation using the DRCm, SRC, and CBTC.

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