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Objective: To investigate the maximum anti-pullout force and stress distribution of cortical bone trajectory (CBT) screws during screw pullout after contacting different cortical bone layers by finite element analysis (FEA) based on Abaqus software, and to provide evidence for increasing screw holding force during CBT screw implantation in clinical practice. Methods: Based on the plain CT data of lumbar spine of a healthy male volunteer who visited the Fourth People's Hospital of Guiyang in June 2022, and the standard screw parameters according to cortical bone trajectory screws. A three-dimensional model of L4 vertebral body and CBT screw was established. The diagnostic criteria of osteoporosis by quantitative CT of lumbar spine in China were set as 120 mg/cm3 low bone mass model. According to the number of contact layers between screws and cortical bone, the models were divided into group A: CBT screws produced one layer of cortical bone contact with the vertebral body (screw implantation point); group B: CBT pedicle screws produced two layers of cortical bone contact with the vertebral body (screw implantation point + pedicle inner edge); group C: CBT pedicle screws produced three layers of cortical bone contact with the vertebral body (screw implantation point + pedicle inner edge + outer edge of the vertebral body); group D: CBT pedicle screws produced four layers of cortical bone contact with the vertebral body (screw implantation point + pedicle upper wall + pedicle lateral wall + upper edge of the vertebral body); group E: CBT pedicle screws produced five layers of cortical bone contact with the vertebral body (screw implantation point + pedicle posteromedial medial wall + anterolateral wall of the pedicle + upper edge of the vertebral body + outer edge of the vertebral body). According to the reference, after the material assignment was completed, the axial pullout force experiment of screws was simulated on Abaqus CEA engineering software for five groups of finite element models established to observe the maximum axial pullout force of each group of models and the stress distribution of screws and vertebral bodies. For the comparative analysis between each group of models corresponding to the measured data, one-way analysis of variance was used. Results: The stress of cancellous bone failure in finite element model of group E was (8.6 ± 0.9), (8.4 ± 0.9), (8.1 ± 0.9), (8.3 ± 0.8), and (8.8 ± 0.7) MPa, respectively, and there was no significant difference between any group (P > 0.05); the maximum principal stress in the tail of screw was (195.1 ± 35.8), (290.9 ± 32.1), (317.3 ± 44.5), (396.3 ± 51.2), and (526.5 ± 53.1) MPa, respectively, and the stress in cortical bone destruction was (40.6 ± 3.5), (52.6 ± 4.2), (89.4 ± 4.9), (109.0 ± 8.3), and (129.4 ± 6.4) MPa, respectively, and there was significant difference between any group (P < 0.05); the maximum axial pullout force in group A-E was (1890.5 ± 45.0), (1913.4 ± 53.8), (2371.0 ± 108.3), (237.2 ± 43.0), and (119.5 ± 43.0), respectively. The increases were 2%, 16%, 5%, and 7%. There were significant differences between each group and group E (P < 0.05). Conclusion: Axial pullout force increases as the number of contact layers between CBT screws and cortical bone increases. The axial pullout force increases most when the cortical trajectory screw contacts the vertebral body with three layers of cortical bone, and reaches the maximum value when the number of contact layers reaches five layers, regardless of the screw tail stress and the maximum axial pullout force, so it is clinically desirable to make the screw contact more than three layers of cortical bone to obtain higher stability during screw implantation, improve screw stability, and increase the surgical fusion rate.
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Background: Studies of clinical outcomes that compare the Medial Pivot design (MP) with the Posterior-Stabilized design (PS) were controversial. The meta-analysis was performed to summarize existing evidence, aiming to determine whether MP was superior to PS prosthesis. Methods: Search strategies followed the recommendations of the Cochrane collaboration. Electronic searches such as PubMed, Embase, Web of Science, and Cochrane were systematically searched for publications concerning medical pivot and posterior stabilized prosthesis from the inception date to April 2021. Authors also manually checked and retrieved a reference list of included publications for potential studies, which the electronic searches had not found. Two investigators independently searched, screened, and reviewed the full text of the article. Disagreements generated throughout the process were resolved by consensus, and if divergences remain, they were arbitrated by a third author. Subsequently, patients were divided into the MP and PS groups. Results: This study included 18 articles, comprising a total of 2614 patients with a similar baseline. The results showed the PS group had a higher risk of the patellar clunk or crepitus. However, the theoretical advantages of MP prosthesis could not translate to the difference in knee function, clinical complications, revision rate and satisfaction. Similarly, the shape and mechanism of prostheses could not affect the implant position and postoperative alignment. Conclusions: The MP prosthesis can reduce the patellar clunk or crepitus rate. However, choices between the MP and PS prosthesis would not affect knee function, clinical complications, revision rate, patient satisfaction, implant position, and postoperative alignment.
RESUMO
Herbivore induced plant volatiles (HIPVs) are key components of plant-herbivorous-natural enemies communications. Indeed, plants respond to herbivores feeding by releasing HIPVs to attract natural enemies. The present study analyses the effect of HIPVs of Vitex negundo (Lamiaceae), an indigenous plant species in northern China, on the predatory ladybug species Harmonia axyridis. Y-tube olfactometer bioassay showed that H. axyridis adults were significantly attracted by V. negundo infested by the aphid Aphis gossypii. We analyzed and compared volatile profiles between healthy and A. gossypii infested V. negundo, screened out the candidate active HIPVs mediated by A. gossypii which could attract H. axyridis, and tested the olfactory behavior of the candidate active compounds on H. axyridis. The gas chromatography-mass spectrometry analysis showed that five volatile compounds were significantly up-regulated after V. negundo infestation by A. gossypii, and five substances were significantly down-regulated in the terpenoid biosynthesis pathway. The olfactory behavior response showed that H. axyridis has significant preference for sclareol, eucalyptol, nonanal and α-terpineol, indicating that this chemical compounds are the important volatiles released by V. negundo to attract H. axyridis. This study preliminarily clarified that V. negundo release HIPVs to attract natural enemies when infected by herbivorous insects. The description of the volatile emission profile enriches the theoretical system of insect-induced volatile-mediated plant defense function of woody plants. Applications in crop protection would lie in designing original strategies to naturally control aphids in orchards.