Čada Radek, Frydrýšek Karel, Sejda František, Demel Jiří, Pleva Leopold
Department of Mechanical Technology, Faculty of Mechanical Engineering, VSB - Technical University of Ostrava, 17. Listopadu 2172/15, 708 33 Ostrava, Czech Republic.
Department of Applied Mechanics, Faculty of Mechanical Engineering, VSB - Technical University of Ostrava, 17. Listopadu 2172/15, 708 33 Ostrava, Czech Republic.
J Med Biol Eng. 2017;37(4):612-625. doi: 10.1007/s40846-017-0279-4. Epub 2017 Jun 21.
Paper focuses on biomechanics, specifically on locking cortical bone screws in angularly stable plates used for the treatment of bone fractures in the medical fields of traumatology and orthopaedics. During extraction of titanium-alloy implants, problems are encountered in an effort to loosen some locking bone screws from the locking holes of an angularly stable plate and the subsequent stripping of the internal hexagon of the screw head. The self-locking of the screw-plate threaded joint was verified by calculation and the effect of the angle of the thread on the head of the locking cortical bone screw on self-locking was evaluated. The magnitude of the torque, causing the stripping of the internal hexagon (the Inbus type head) of a locking cortical bone screw with a shank diameter of 3.5 mm from Ti6Al4 V titanium alloy to ISO 5832-3, was determined experimentally. Also, it was experimentally found that the rotation of the screwdriver end with a hexagonal tip inside the locking cortical bone screw head during stripping of the internal hexagon causes strain of the screw head perimeter and thereby an increase of thread friction. The effect of tightening torque on the possibility of loosening of the locking cortical bone screw from the locking hole of an angularly stable plate was assessed experimentally. From the evaluation of five alternative shapes of locking cortical bone screw heads in terms of the acting stress and generated strains, it follows that the best screw is the screw with the Torx type head, which demonstrates the lowest values of reduced stress and equivalent plastic strain. Based on experiments and simulations the authors recommend that all global producers of locking cortical bone screws for locking holes of angularly stable plates use the Torx type heads, and not heads of the Inbus type or the Square, PH, PZ types.
本文聚焦于生物力学，具体研究用于创伤学和矫形外科学等医学领域治疗骨折的角度稳定钢板中锁定皮质骨螺钉。在钛合金植入物取出过程中，从角度稳定钢板的锁定孔中松开一些锁定骨螺钉以及随后螺钉头部内六角脱扣时会遇到问题。通过计算验证了螺钉 - 钢板螺纹连接的自锁性能，并评估了锁定皮质骨螺钉头部螺纹角度对自锁的影响。通过实验确定了将直径为3.5毫米、由Ti6Al4V钛合金制成并符合ISO 5832 - 3标准的锁定皮质骨螺钉的内六角（内梅花型头部）脱扣所需的扭矩大小。此外，实验还发现，在内六角脱扣过程中，锁定皮质骨螺钉头部内带有六角尖端的螺丝刀端部旋转会导致螺钉头部周边产生应变，从而增加螺纹摩擦力。通过实验评估了拧紧扭矩对锁定皮质骨螺钉从角度稳定钢板锁定孔中松动可能性的影响。从对五种替代形状的锁定皮质骨螺钉头部的作用应力和产生应变的评估来看，最佳的螺钉是带有梅花型头部的螺钉，其显示出最低的折算应力值和等效塑性应变值。基于实验和模拟，作者建议所有生产用于角度稳定钢板锁定孔的锁定皮质骨螺钉的全球制造商使用梅花型头部，而非内梅花型、方型、十字槽型、米字槽型头部。
