Renard A J S, Schutte B G, Verdonschot N, van Kampen A
Department of Orthopaedics, University Medical Center Nijmegen, P.O. Box 9101, NL-6500 HB Nijmegen, The Netherlands.
Clin Biomech (Bristol). 2005 Dec;20(10):1126-30. doi: 10.1016/j.clinbiomech.2005.07.007. Epub 2005 Oct 6.
Maintenance of wire pretension in an Ilizarov external fixator is dependent on the torque applied to the fixation bolts. We therefore measured immediately after surgery the clinically applied torques. The median value was only 10 N m (range 8-14N m). We wondered whether this value is appropriate to maintain the wire pretension and thereby to achieve sufficient fracture stability during dynamic loading of the device for a longer period.
A material testing machine dynamically loaded one wire mounted on one ring. Several configurations were tested.
A quick decrease in wire tension to a steady state situation was seen. In the most stable configuration (20 N m wire fixation torque) 50% of the initial 90 kg wire pretension remained after dynamic loading with 200 N. In the least stable configuration (10 N m torque) considerable wire slippage occurred even without loading and no tension remained after loading! No plastic deformation of the wires was observed so loss of wire tension was due to slippage of the wires through the fixation bolts.
With the small fixation torques used in clinical practice considerable wire tension is lost even after a few loading cycles. Further research should address the question whether preservation of a higher wire tension during long term loading promotes faster fracture healing.
伊里扎洛夫外固定器中钢丝预紧力的维持取决于施加在固定螺栓上的扭矩。因此，我们在术后立即测量了临床应用的扭矩。中位数仅为10 N·m（范围8 - 14 N·m）。我们想知道这个值是否适合维持钢丝预紧力，从而在装置动态加载较长时间期间实现足够的骨折稳定性。
一台材料试验机对安装在一个环上的一根钢丝进行动态加载。测试了几种配置。
观察到钢丝张力迅速下降至稳定状态。在最稳定的配置（钢丝固定扭矩20 N·m）中，在200 N动态加载后，初始90 kg钢丝预紧力的50%得以保留。在最不稳定的配置（扭矩10 N·m）中，即使没有加载也发生了相当大的钢丝滑动，加载后没有剩余张力！未观察到钢丝的塑性变形，因此钢丝张力的损失是由于钢丝在固定螺栓中滑动所致。
在临床实践中使用的小固定扭矩下，即使经过几次加载循环，钢丝张力也会大量损失。进一步的研究应探讨在长期加载过程中保持较高钢丝张力是否能促进骨折更快愈合这一问题。
