Buma P, van Loon P J, Versleyen H, Weinans H, Slooff T J, de Groot K, Huiskes R
Institute of Orthopaedics, Orthopaedic Research Laboratory, University Hospital Nijmegen, The Netherlands.
Biomaterials. 1997 Sep;18(18):1251-60. doi: 10.1016/s0142-9612(97)00064-1.
We hypothesized that reduced stem stiffness of orthopaedic implants contributes to a high risk of loosening, since interface stresses and relative motions may exceed a tolerable range. To study this hypothesis, three types of load-bearing implant with different stiffnesses were inserted into the tibia of the goat. Histological analysis was performed of bone repair after insertion of the implant, bone ingrowth, interface disruption and loosening. A finite element model of the configuration provided the quantitative range of interface stresses and relative motions for the present experiment. The implants were made out of stainless steel, hollow titanium and a thin titanium core covered with a polyacetal coating. The stiffness ratios of these implants were approximately 10:4:1, respectively. All implants were coated with a layer of hydroxyapatite (HA) in order to minimize the possible biological effects of the different implant materials. Irrespective of the type of implant, there was a repair phase that lasted 6-12 weeks. The stiff implants functioned well. Large areas of bone bonding to the HA layer were found after the repair phase at 12 weeks postoperatively. After 24 weeks, some signs of loosening were observed. More loosening occurred with the hollow titanium and polyacetal implants, mainly during the repair phase. Three hollow titanium and three polyacetal coated implants survived this period, and were killed after 24 weeks. The integrity of the HA layer at the bone-implant interface of the titanium implants was good. In the polyacetal implants, the repair reaction of the cortical bone was incomplete. Bone ingrowth into HA was largely lacking. In conclusion, we found significant differences in the repair and interface reactions around implants of different stiffness. Stiff implants showed favourable initial interface conditions for bone ingrowth. Intermediate and flexible implants provoked unfavourable interface conditions for initial bone ingrowth. The finite element study showed that the flexible stems produce larger micromotions and higher interface stresses at the bone-prosthesis interface than the stiff stems, indicating an explanation for the histological findings.
我们推测，骨科植入物的杆刚度降低会导致松动风险增加，因为界面应力和相对运动会超过可耐受范围。为了研究这一推测，将三种不同刚度的承重植入物植入山羊胫骨。对植入物植入后的骨修复、骨长入、界面破坏和松动情况进行了组织学分析。该构型的有限元模型给出了本实验中界面应力和相对运动的定量范围。植入物由不锈钢、空心钛以及覆盖有聚缩醛涂层的薄钛芯制成。这些植入物的刚度比分别约为10:4:1。所有植入物均涂有一层羟基磷灰石（HA），以尽量减少不同植入材料可能产生的生物学效应。无论植入物类型如何，都有一个持续6 - 12周的修复阶段。刚性植入物功能良好。术后12周修复阶段结束后，发现大面积骨与HA层结合。24周后，观察到一些松动迹象。空心钛和聚缩醛植入物出现了更多松动，主要发生在修复阶段。三根空心钛和三根涂有聚缩醛的植入物在此期间存活下来，并在24周后处死。钛植入物骨 - 植入物界面处HA层的完整性良好。在聚缩醛植入物中，皮质骨的修复反应不完全。HA中基本没有骨长入。总之，我们发现不同刚度植入物周围的修复和界面反应存在显著差异。刚性植入物显示出有利于骨长入的初始界面条件。中等刚度和柔性植入物引发了不利于初始骨长入的界面条件。有限元研究表明，柔性杆在骨 - 假体界面处产生的微动比刚性杆更大，界面应力更高，这为组织学研究结果提供了解释。
