Khalaf Kinda, Azhang Arash, Cheng Chih-Hsiu, Nikkhoo Mohammad
Department of Biomedical Engineering, Health Engineering Innovation Center, Khalifa University of Science and Technology, Abu Dhabi P.O. Box 127788, United Arab Emirates.
Department of Biomedical Engineering, Science and Research Branch, Islamic Azad University, Tehran 1477893855, Iran.
Materials (Basel). 2023 Aug 4;16(15):5470. doi: 10.3390/ma16155470.
Enhancing the design of bone screw head sockets to prevent stripping and improve the torque required for smooth unscrewing is a significant challenge in orthopedic applications. This research aims to establish a quantitative methodology by integrating mechanical testing with finite element (FE) simulations to determine a safe limitation depth for the screwdriver when engaging with the hexagonal socket, thus avoiding stripped screw heads. A FE model was developed to investigate the biomechanical responses of the screw head design. Five custom-made hexagonal sockets were manufactured, and single load torsional tests were conducted to assess the mechanical performance of the screws and drivers. The results from the mechanical tests were compared with the FE simulations, demonstrating a close agreement and confirming the model's validity. Furthermore, additional FE models were created to study the impact of manufacturing tolerances on the socket width and screwdriver width. The findings revealed that the maximum torque to failure for the four designs was lower than the margins specified in ISO 6475. Additionally, increasing the depth of the screwdriver led to higher maximum torque values. This research suggests that the technique of screw insertion, specifically the depth of the driver tool within the screw socket, holds greater importance in preventing stripped screw heads than the design and manufacturing width of the bone screw's hexagonal socket and screwdriver. This confirms the importance of screwdriver engagement inside the bone screw socket to prevent stripped screw heads and sheds light on the added value of maximum torque prediction for future design modifications.
改进骨螺钉头部内六角孔的设计，以防止滑丝并提高顺利拧松所需的扭矩，是骨科应用中的一项重大挑战。本研究旨在通过将力学测试与有限元（FE）模拟相结合，建立一种定量方法，以确定螺丝刀与六角孔啮合时的安全极限深度，从而避免螺钉头部滑丝。开发了一个有限元模型来研究螺钉头部设计的生物力学响应。制造了五个定制的六角孔，并进行了单载荷扭转试验，以评估螺钉和螺丝刀的力学性能。将力学测试结果与有限元模拟结果进行比较，结果显示二者吻合度很高，证实了模型的有效性。此外，还创建了额外的有限元模型，以研究制造公差对孔宽度和螺丝刀宽度的影响。研究结果表明，四种设计的最大破坏扭矩均低于ISO 6475规定的余量。此外，增加螺丝刀的深度会导致最大扭矩值更高。本研究表明，螺钉插入技术，特别是螺丝刀工具在螺钉孔内的深度，在防止螺钉头部滑丝方面比骨螺钉六角孔和螺丝刀的设计及制造宽度更为重要。这证实了螺丝刀在骨螺钉孔内的啮合对于防止螺钉头部滑丝的重要性，并为未来设计改进中最大扭矩预测的附加价值提供了启示。
