Biliouris T L, Schneider E, Rahn B A, Gasser B, Perren S M
M. E. Müller-Institute for Biomechanics, University of Bern, Switzerland.
J Orthop Trauma. 1989;3(4):323-32. doi: 10.1097/00005131-198912000-00012.
The most common complication of external fixation is pin loosening. Preloading the implant-bone interface is believed to retard this process. Radial preload, in particular, may be useful, as it allows loading in more than one direction. To investigate the effect of varying degrees of radial preload on the pin-bone interface, 30 freshly thawed human cadaveric tibiae were sectioned into 4-cm segments. Uniform drill holes were produced in the anterior tibial ridge of all segments and custom experimental bolts, oversized in diameter by as much as 1 mm, were pressed into each specimen. Macroscopic surface fractures were noted at the time of bolt insertion for misfits greater than 0.2 mm. Following histologic preparation, the implant-bone interface was evaluated microscopically based on the appearance of osteonal compression, lamellar distortion, and microfractures. Insertion of external fixator pins with misfits of greater than 0.4 mm resulted in significant microscopic structural damage to the bone surrounding the pin. High degrees of radial preload, exceeding the elastic limit of cortical bone, may be produced around pin holes by a small misfit. The use of oversized pins or screws must therefore be questioned.
外固定最常见的并发症是钢针松动。预加载植入物-骨界面被认为可以延缓这一过程。特别是径向预加载可能会有帮助，因为它允许在多个方向上加载。为了研究不同程度的径向预加载对钢针-骨界面的影响，将30根新鲜解冻的人体尸体胫骨切成4厘米长的节段。在所有节段的胫骨前嵴上钻出均匀的钻孔，并将直径最大加大1毫米的定制实验螺栓压入每个标本中。对于大于0.2毫米的不匹配情况，在螺栓插入时记录宏观表面骨折情况。经过组织学制备后，根据骨单位压缩、板层变形和微骨折的表现对植入物-骨界面进行微观评估。插入不匹配大于0.4毫米的外固定器钢针会导致钢针周围骨组织出现明显的微观结构损伤。小的不匹配可能会在针孔周围产生超过皮质骨弹性极限的高度径向预加载。因此，使用加大尺寸的钢针或螺钉必须受到质疑。
