To compare the CT values and length of the screw tracks of traditional trajectory (TT), cortical bone trajectory (CBT), and modified cortical bone trajectory (MCBT) screws and investigate the effects on the biomechanics of lumbar fixation.CT scan data of 60 L4 and L5 lumbar spine were retrieved and divided into 4 groups (10 male and 10 female cases in the 20-30 years old group and 20 male and 20 female cases in the 30-40 years old group). 3-dimentional (3D) model were established using Mimics 19.0 for each group and the placement of three techniques was simulated on the L4 and L5, and the part of the bone occupied by the screw track was set as the region of interest (ROI). The mean CT value and the actual length of the screw track were measured by Mimics 19.0.The CT values of ROI for the three techniques were significantly different between the same gander in each age group (P < 0.05). The difference of screw track lengths for CBT and MCBT in the male and female is significant (P < 0.05).According to the CT values of the three screw tracks: MCBT > CBT > TT, the MCBT screw track has greater bone-screw surface strength and longer screw tracks than CBT, which is easier to reach the anterior column of the vertebral body contributing to superior biomechanical properties. 

https://bmcsurg.biomedcentral.com/counter/pdf/10.1186/s12893-022-01893-5

Comparison of CT values in traditional trajectory, traditional cortical bone trajectory, and modified cortical bone trajectory

Modified cortical bone trajectory (MCBT) technique was proposed by our team in previous studies, but its biomechanical properties at adjacent segments have not been discussed yet. Therefore, the purpose of this study is to investigate the biomechanical properties of modified cortical bone trajectory (MCBT) technique on adjacent segment degeneration (ASD) in transforaminal intradiscal lumbar disc fusion (TLIF) compare to traditional bone trajectory (TT) technique and cortical bone trajectory (CBT) technique.The four human cadaveric lumbar specimens were provided by the anatomy teaching and research department of Xinjiang Medical University and four intact finite element models of the L1-S1 segment were generated. For each of these, three transforaminal lumbar interbody fusion procedures with three different fixation techniques were reconstructed at the L4-L5 segment, as follows: TT-TT (TT at both L4 and L5 segments), CBT-CBT (CBT at both L4 and L5 segments), MCBT-MCBT (MCBT at both L4 and L5 segments). The range of motion and von Mises stress of the intervertebral disc of the L3-L4 and L5-S1 segments were recorded with a 400N compressive load and 7.5 Nm moments in flexion, extension, left-right bending, and left-right rotation.The peak ROM of the L3-L4 segment in the MCBT-MCBT group was reduced by 10.5%, 6.1%, 12.2%, 4.1%, and 1.5% in flexion, extension, left-right bending, and left rotation compared to the TT-TT group and reduced by 1.8%, 5.5%, 10.0%, 12.8%, and 8.8% in flexion, left-right bending, and left-right rotation compared to the CBT-CBT group, respectively. The MCBT-MCBT group has the lowest peak ROM of the L3-L4 segment in flexion, left bending, and right rotation, the lowest peak ROM of the L5-S1 segment in extension and right rotation, and the lowest peak von Mises stress of the intervertebral disc at the L5-S1 segment in right rotation compared to the TT-TT and CBT-CBT group. In addition, the peak von Mises stress at the L3-L4 segment was lowest and more dispersed in all motions, the MCBT-MCBT group exhibited lower peak ROM of the L5-S1 segment in flexion, extension, and right rotation, and showed lower peak von Mises stress of the disc at the L5-S1 segment in flexion, extension, and right rotation compared with the TT-TT group.The modified cortical bone trajectory technique may have a beneficial effect on reducing the incidence of ASD in the L4-L5 TLIF model compared to the traditional bone trajectory technique and cortical bone trajectory technique. 

Biomechanical evaluation of modified and traditional cortical bone trajectory technique on adjacent segment degeneration in transforaminal lumbar interbody fusion—finite element analysis

Abstract Background We aimed to investigate the biomechanical properties of the cortical bone trajectory (CBT) and modified cortical bone trajectory (MCBT) on the osteoporotic lumbar spine with the finite element method. Methods Four osteoporotic specimens were selected to establish the L4 vertebral body model. For the CBT, a screw with a diameter of 6.0 mm and a length of 35 mm was used, while for the MCBT, a screw with a diameter of 4.5 mm and a length of 40 mm was used. Two screws with different trajectories were inserted into the pedicles on the different sides of the same vertebral body. The axial pull-out strength, stability of the screw, and the stability of the vertebral body were compared. Results The pull-out strength of the MCBT (1620.00 ± 40.67N) was significantly higher than CBT (1360.25 ± 44.70N) (p &lt; 0.001), and the stability of the MCBT screws in the upper, lower, left, and right direction was significantly higher than the CBT (p = 0.043; p = 0.027; p = 0.023; p = 0.035). The stability of the vertebral body with MCBT in axial rotation, and lateral bending was significantly higher than CBT (p = 0.005; p = 0.011). However, there was no significant difference in flexion and extension between the two groups (p &gt; 0.05). Conclusion MCBT might be a choice for internal fixation of the lumbar spine in patients with osteoporosis. 

/pdf/biomechanical-investigation-of-traditional-and-modified-1iou98ub.pdf

Biomechanical investigation of traditional and modified cortical bone trajectory for osteoporosis lumbar spine - finite element analysis

Abstract Background: To compare the CT values and length of the screw tracks of traditional trajectory (TT), cortical bone trajectory (CBT), and modified cortical bone trajectory (MCBT) screws and investigate the effects on the biomechanics of lumbar fixation. Methods: CT scan data of 60 L4 and L5 lumbar spine were retrieved and divided into 4 groups (10 male and 10 female cases in the 20-30 years old group and 20 male and 20 female cases in the 30-40 years old group). 3-dimentional (3D) model were established using Mimics 19.0 for each group and the placement of three techniques was simulated on the L4 and L5, and the part of the bone occupied by the screw track was set as the region of interest (ROI). The mean CT value and the actual length of the screw track were measured by Mimics 19.0. Results: The CT values of ROI for the three techniques were significantly different between the same gander in each age group (P＜0.05). The difference of screw track lengths for CBT and MCBT in the male and female is significant (P＜0.05). Conclusions: According to the CT values of the three screw tracks: MCBT &gt; CBT &gt; TT, the MCBT screw track has greater bone-screw surface strength and longer screw tracks than CBT, which is easier to reach the anterior column of the vertebral body contributing to superior biomechanical properties. 

The study aimed to investigate the impact of posterior element and ligament removal on the maximum von Mises stress, and maximum shear stress of the eight-layer annulus for treating stenosis at the L3-L4 and L4-L5 levels in the lumbar spine. Previous studies have indicated that laminectomy alone can result in segmental instability unless fusion is performed. However, no direct correlations have been established regarding the impact of posterior and ligament removal. To address this gap, four models were developed: Model 1 represented the intact L2-L5 model, while model 2 involved a unilateral laminotomy involving the removal of a section of the L4 inferior lamina and 50% of the ligament flavum between L4 and L5. Model 3 consisted of a complete laminectomy, which included the removal of the spinous process and lamina of L4, as well as the relevant connecting ligaments between L3-L4 and L4-L5 (ligament flavum, interspinous ligament, supraspinous ligament). In the fourth model, a complete laminectomy with 50% facetectomy was conducted. This involved the same removals as in model 3, along with a 50% removal of the inferior/superior facets of L4 and a 50% removal of the facet capsular ligaments between L3-L4 and L4-L5. The results indicated a significant change in the range of motion (ROM) at the L3-L4 and L4-L5 levels during flexion and torque situations, but no significant change during extension and bending simulation. The ROM increased by 10% from model 1 and 2 to model 3, and by 20% to model 4 during flexion simulation. The maximum shear stress and maximum von-Mises stress of the annulus and nucleus at the L3-L4 levels exhibited the greatest increase during flexion. In all eight layers of the annulus, there was an observed increase in both the maximum shear stress and maximum von-Mises stress from model 1&2 to model 3 and model 4, with the highest rate of increase noted in layers 7&8. These findings suggest that graded posterior element and ligament removal have a notable impact on stress distribution and range of motion in the lumbar spine, particularly during flexion.

Effect of graded posterior element and ligament removal on annulus stress and segmental stability in lumbar spine stenosis: a finite element analysis study

Purpose: To evaluate the biomechanics effect of modified cortical bone screw technique (MCBT) with other traditional internal fixation systems on lumbar osteoporotic wet specimen. Methods: Four different finite element models were established using CT data: (1) lumbar osteoporosis model without internal fixation system; (2) traditional pedicle screw technology (TT) model; (3) traditional cortical bone screw technology (CBT) model; (4) MCBT model. The changes of global displacement, intervertebral disc displacement of all models and internal fixation system Von Mises stress among the three models were compared under the same physiological load. Results: Compared with the other three models, the total displacement of the modified CBT screw model was the smallest, with the maximum displacement of 0.216 mm; The intervertebral disc displacement of the modified CBT screw model was the smallest, with the maximum displacement of 0.149 mm; the internal fixation system Von Mises stress of the modified CBT screw technique model was the largest compared with the other three models, The maximum Von Mises stress is 232.73 MPa. Conclusion: Compared to traditional pedicle screw and traditional CBT, MCBT has better mechanical stability, and it is of certain clinical application value.

Finite element analysis of human lumbar vertebrae in internal fixation system model with different bone density trajectories

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Finite element analysis of human lumbar vertebrae in internal fixation system model with different bone density trajectories