Key Takeaways & Executive Findings
- •• Bone cement-augmented cortical bone trajectory (CBT) screws demonstrated superior axial pullout force compared to both modified variable-diameter all-cortical bone screws and un-augmented CBT screws. • In terms of screw stability under inferior loading, the augmented CBT group showed the highest load-displacement ratio, followed by the modified group, with the un-augmented group lowest. • Vertebral range of motion was reduced in both augmented and modified CBT groups compared to un-augmented, but no significant difference was found between augmented and modified groups. • The bone cement-augmented CBT technique may be a more appropriate choice for internal fixation in osteoporotic patients, offering better biomechanical performance than the novel variable-diameter screw.
Abstract
BACKGROUND: The scarcity of bone trabecular structures caused by osteoporosis is not enough to maintain screw holding power, which often leads to the failure of internal fixation surgery. The screw holding power is often increased by increasing the diameter and length of screws, changing the surface coating of screws, and reinforcing the nail track with bone cement. The cement reinforced cortical bone track nailing technique and the modified cortical bone track nailing technique using a new type of variable diameter screw have been proven to have good fixation effects, and now the related mechanical properties of the two need to be analyzed and compared. OBJECTIVE: Finite element analysis was used to compare the mechanical properties of bone cement-strengthened cortical bone trajectory nailing technology, cortical bone trajectory nailing technology, and modified cortical bone trajectory nailing technology using a new variable-diameter total cortical bone thread screw in lumbar spine internal fixation surgery. METHODS: Based on the CT scan data processing of three osteoporotic vertebrae, the L4 lumbar spine model was constructed, and the innovative variable-diameter all-cortical bone screw was applied in the modified cortical bone nailing technique, with the screw having a total length of 45 mm and a diameter varying from 5.5 to 4.3 mm. This was compared with the un-augmented cortical bone trajectory group (diameter 5.5 mm, length 40 mm) and the bone cement-augmented cortical bone trajectory group (diameter 5.5 mm, length 40 mm, central hole diameter 1 mm). The fixation strength of each group was compared by measuring axial pullout force, screw stability (load-displacement ratio in superior, inferior, left, and right directions), and vertebral range of motion. RESULTS AND CONCLUSION: (1) Axial pullout force: augmented cortical bone trajectory group > modified cortical bone trajectory screw group (P=0.0246), and both augmented and modified groups were greater than the un-augmented cortical bone trajectory group (P=0.0001 and P=0.00264, respectively). (2) Screw stability: when load was applied inferiorly, the load-displacement ratios were augmented cortical bone trajectory group > un-augmented and modified groups (all P < 0.05), and modified group > un-augmented group (P < 0.05). (3) Vertebral range of motion: under five loading conditions, the augmented cortical bone trajectory group showed less motion than the modified group, but the differences were not statistically significant (P > 0.05), and both augmented and modified groups showed less motion than the un-augmented group. (4) Compared with the modified group, the augmented group showed improved mechanical properties in screw load-displacement ratio and lumbar range of motion, but the differences were not statistically significant (P > 0.05). (5) These findings suggest that the bone cement-augmented cortical bone trajectory technique has better biomechanical properties than the new variable-diameter all-cortical bone screw, and may be a more suitable screw placement option for internal fixation in patients with osteoporosis.
1. Introduction
Osteoporosis has become a public health issue both domestically and globally [1-3], and the number of elderly osteoporotic patients requiring surgical treatment for lumbar problems continues to rise. Pedicle screw fixation has become one of the main techniques for treating various spinal diseases due to its ability to stabilize the spine [4]. Studies have confirmed that the stability of pedicle screws is related to bone mineral density; low bone density can lead to screw loosening, displacement, and even pullout, resulting in fixation failure [5-6]. Patients with failed fixation may require revision surgery, with reported revision rates of 8%-45% in osteoporotic patients [7]. Therefore, it is necessary to take measures to enhance screw holding power in osteoporotic vertebrae. Bone cement augmentation is an effective method to enhance pedicle screw holding power, and the commonly used polymethyl methacrylate bone cement can improve screw fixation efficacy and stability [8]. However, injected bone cement may leak through blood vessels or gaps in the vertebral body, especially in cases of severe vertebral destruction such as severe burst fractures, increasing the risk of leakage.
The augmentation site of bone cement pedicle screws is mainly located in the vertebral body. To reduce the risk of cement leakage, alternative techniques have been developed, such as cortical bone trajectory (CBT) screws, which engage the cortical bone of the pedicle and vertebral body, and modified CBT techniques using novel screw designs. This study aims to compare the biomechanical performance of bone cement-augmented CBT, standard CBT, and a modified CBT using a new variable-diameter all-cortical bone screw in lumbar internal fixation, using finite element analysis.
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Xie Xuechen, Julaiti·Maitirouzi, Li Chunchao, Zhang Le, Wang Yixi, Paerhati·Rexiti (2026). Mechanical analysis of a bone cement-augmented cortical bone trajectory screw versus a new variable-diameter all-cortical bone screw. Chinese Journal of Tissue Engineering Research. https://doi.org/10.12307/2026.21389
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Frequently Asked Questions
What is the purpose of this study?
The study compares the mechanical properties of three lumbar internal fixation techniques: bone cement-augmented cortical bone trajectory (CBT), standard CBT, and a modified CBT using a new variable-diameter all-cortical bone screw, using finite element analysis.
How was the finite element model constructed?
An L4 lumbar vertebra model was constructed based on CT scans of three osteoporotic vertebrae. The model was processed using Mimics, Geomagic, Solidworks, and Ansys Workbench for mesh generation, material assignment, and simulation.
What were the main outcome measures?
The main outcome measures were axial pullout force, screw stability (load-displacement ratio in four directions), and vertebral range of motion under various loading conditions.
Which technique showed the best biomechanical performance?
The bone cement-augmented CBT technique showed the highest axial pullout force and generally better stability compared to the other two techniques, suggesting it may be more suitable for osteoporotic patients.
What are the clinical implications of this study?
The findings suggest that bone cement augmentation may provide superior fixation in osteoporotic vertebrae, potentially reducing the risk of screw loosening and revision surgery. However, the modified variable-diameter screw also showed promising results, offering an alternative that avoids cement-related complications.
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