Department of Neurosurgery, University Medicine Greifswald, Greifswald, Germany.
Department of Neurosurgery, University Medicine Greifswald, Greifswald, Germany.
Clin Biomech (Bristol). 2020 Jul;77:105049. doi: 10.1016/j.clinbiomech.2020.105049. Epub 2020 May 25.
Lag screw osteosynthesis in odontoid fractures shows a high rate of pseudarthrosis. Biomechanical properties may play a role with insufficient fragment compression or unnoticed screw stripping. A biomechanical comparison of different constructed lag-screws was carried out and the biomechanical properties determined.
Two identical compression screws with different pilot holes (1.25 and 2.5 mm), a double-threaded screw and one sleeve-nut-screw were tested on artificial bone (Sawbone, densities 10-30pcf). Fragment compression and torque were continuously measured using thin-film force sensors (Flexiforce A201, Tekscan) and torque sensors (PCE-TM 80, PCE GmbH).
The lowest compression reached the double-threaded screw. Compression and sleeve-nut-screw achieved 214-298% and 325-546%, respectively, of the compression force of double-threaded-screw, depending on the test material. The pilot hole optimization led to a significant improvement in compression only in the densest test material. Screw stripping took place significantly later with increasing density of the test material on all screws. In compression screws this was done at a screw rotation of 180-270°, in sleeve nut screw at 270-720° and in double-threaded screws at 300-600° after reaching the maximum compression.
Double-threaded screw is robust against screw stripping, but achieves only low fragment compression. The classic compression screws achieve better compression, but are sensitive to screw stripping. Sleeve-nut screw is superior in compression and as robust as double-threaded screw against screw stripping. Whether the better biomechanical properties lead to a reduction in pseudarthrosis must be proven in clinical trials.
齿状突骨折的拉力螺钉内固定术后假关节形成率较高。生物力学性能可能在骨折块压缩不足或螺钉切出未被察觉的情况下起作用。本研究对不同构型的拉力螺钉进行了生物力学比较，并确定了其生物力学特性。
在人造骨（Sawbone，密度为 10-30pcf）上测试了两种具有不同导孔（1.25 和 2.5mm）的相同压缩螺钉、一种双螺纹螺钉和一个套筒螺母螺钉。使用薄膜力传感器（Flexiforce A201，Tekscan）和扭矩传感器（PCE-TM 80，PCE GmbH）连续测量骨折块压缩和扭矩。
最低的压缩力达到了双螺纹螺钉。根据测试材料的不同，压缩螺钉和套筒螺母螺钉的压缩力分别达到了双螺纹螺钉的 214%-298%和 325%-546%。导孔优化仅在最致密的测试材料中显著提高了压缩力。随着测试材料密度的增加，所有螺钉的螺钉切出发生得都明显更晚。在压缩螺钉中，螺钉旋转 180-270°时发生螺钉切出，在套筒螺母螺钉中，螺钉旋转 270-720°时发生螺钉切出，在双螺纹螺钉中，螺钉旋转 300-600°时达到最大压缩后发生螺钉切出。
双螺纹螺钉抗螺钉切出能力强，但仅能实现较低的骨折块压缩。经典的压缩螺钉具有更好的压缩效果，但对螺钉切出较为敏感。套筒螺母螺钉在压缩方面表现更佳，且抗螺钉切出能力与双螺纹螺钉相当。更好的生物力学性能是否会导致假关节减少，必须通过临床试验来证明。
