Key Takeaways & Executive Findings
- •• Both cortical bone trajectory (CBT) and modified cortical bone trajectory (MCBT) screw placement techniques significantly improve the mechanical stability of the fixed segment in lumbar revision surgery, with MCBT showing superior overall performance. • The novel double-screw technique preserves the original internal fixation, reducing surgical trauma and avoiding risks associated with traditional revision methods. • MCBT demonstrated greater reductions in intervertebral disc stress and vertebral body stress compared to CBT, particularly under extension and lateral bending. • Finite element analysis provides a robust framework for evaluating the biomechanical performance of novel spinal fixation techniques, supporting clinical decision-making.
Abstract
BACKGROUND: Currently, in clinical practice, the original internal fixation devices are often removed to perform revision surgery for failed vertebral fixation, which poses certain drawbacks and risks. The pedicle double-screw technique can preserve the original internal fixation devices, while the modified cortical bone trajectory technique offers excellent mechanical performance. Combining these two techniques for revision surgery can mitigate the conventional risks, although the mechanical performance of this new modified cortical bone trajectory technique in revision surgery is not yet well understood. OBJECTIVE: To analyze the mechanical performance of cortical bone trajectory (CBT) and modified cortical bone trajectory (MCBT) screw placement techniques combined with the double-screw technique in lumbar revision surgery using finite element analysis, and to explore the advantages of MCBT over CBT in revision surgery. METHODS: A three-dimensional model of L1-5 vertebrae, endplates, and intervertebral discs was established based on computed tomography data. Screws were placed following the traditional trajectory pedicle screw technique, and the models were divided into traditional trajectory initial group and loosening group based on different screw-bone contact forms. Revision was performed on the traditional trajectory loosening group using MCBT and CBT screws to re-fix the lumbar spine. Finite element analysis was used to evaluate the mechanical performance of MCBT and CBT in revision surgery. RESULTS AND CONCLUSION: (1) Under flexion, extension, lateral bending, and axial rotation, the CBT revision group showed reductions in range of motion (ROM) of 31.97%, 29.15%, 15.12%, and 29.63%, and reductions in intervertebral disc stress of 15.44%, 78.67%, 54.36%, and 40.55%, respectively, compared with the control group. (2) The MCBT revision group showed reductions in ROM of 32.16%, 29.33%, 15.47%, and 31.42%, and reductions in intervertebral disc stress of 16.25%, 83.00%, 64.82%, and 45.83%, respectively, compared with the control group. (3) Compared with the CBT revision group, the MCBT revision group showed reductions in ROM of 0.28%, 0.25%, 0.40%, and 2.54%, reductions in intervertebral disc stress of 0.96%, 20.25%, 22.91%, and 8.88%, reductions in vertebral body stress of 15.78%, 4.75%, 11.22%, and 7.42%, and reductions in screw-rod system stress of 0.15%, 9.80%, 1.04%, and 0.84%, respectively. (4) Both CBT and MCBT techniques effectively enhance the mechanical stability of the fixed segment in lumbar revision surgery, with MCBT showing superior overall performance, providing a new technical option for clinical lumbar revision.
1. Introduction
Traditional trajectory pedicle screw fixation is the gold standard for spinal internal fixation and has been widely used in the treatment of osteoporosis. However, the traditional trajectory does not fully utilize cortical bone, and postoperative pedicle screw loosening occurs in 1%-60% of patients, leading to reduced stability of the fixed segment and potential fixation failure, necessitating revision surgery. Conventional revision methods, such as increasing screw diameter or bone cement augmentation, may temporarily improve fixation strength but carry risks of nerve injury and cement leakage.
Cortical bone trajectory (CBT) screw placement increases screw-cortical bone contact and has gained clinical popularity. To further optimize the use of cortical bone along the entire trajectory, REXITI et al. proposed modified cortical bone trajectory (MCBT) screw placement, which has demonstrated excellent mechanical properties. Previous studies have analyzed revision outcomes after removing the original fixation and using CBT or MCBT, showing both techniques improve lumbar stability, with MCBT not inferior to CBT.
However, replacing internal fixation requires complete exposure and removal of the original device, leading to prolonged operative time, severe soft tissue damage, and increased blood loss. Given the different entry points and trajectories of traditional and CBT screws, combining both trajectories within the same pedicle (double-screw technique) may preserve the original fixation while adding a screw, potentially reducing surgical trauma. This study employs finite element analysis to evaluate the biomechanical performance of this novel double-screw technique in lumbar revision surgery, comparing CBT and MCBT as the added screw.
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ZHANG Le, Julaiti·Maitirouzi, XIE Xuechen, LI Chunchao, WANG Yixi, Parhat·Rexiti (2026). Finite element analysis of biomechanical performance of a novel double-screw technique in lumbar revision of the original fixed segment. Chinese Journal of Tissue Engineering Research. https://doi.org/10.12307/2026.21511
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Frequently Asked Questions
What is the double-screw technique in lumbar revision surgery?
The double-screw technique involves placing two screws with different trajectories within the same pedicle, typically combining traditional pedicle screw trajectory and cortical bone trajectory (CBT) or modified cortical bone trajectory (MCBT). This approach increases cortical bone contact and distributes stress, enhancing fixation stability, especially in osteoporotic vertebrae.
How does the modified cortical bone trajectory (MCBT) differ from cortical bone trajectory (CBT)?
MCBT is an improved version of CBT that optimizes the screw trajectory to better utilize cortical bone along the entire path, providing superior mechanical performance compared to CBT, as demonstrated in finite element analyses.
What are the advantages of preserving the original internal fixation during revision surgery?
Preserving the original fixation reduces surgical trauma, operative time, and blood loss, and avoids risks associated with removing and replacing implants, such as nerve injury and bone cement leakage. The double-screw technique allows for adding a screw without removing the existing one.
What were the main findings of the finite element analysis?
Both CBT and MCBT revision techniques significantly improved the mechanical stability of the fixed segment, with MCBT showing greater reductions in intervertebral disc stress and vertebral body stress compared to CBT, particularly under extension and lateral bending. MCBT also slightly reduced range of motion and screw-rod system stress.
What is the clinical significance of this study?
The study provides evidence that the novel double-screw technique, especially with MCBT, is a viable option for lumbar revision surgery, offering enhanced stability and reduced stress on spinal structures. This is particularly beneficial for elderly patients with osteoporosis, potentially improving surgical outcomes and reducing complications.
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