Stańczyk M, van Rietbergen B
Institute of Fundamental Technological Research, Polish Academy of Sciences, Warsaw, Poland.
J Biomech. 2004 Dec;37(12):1803-10. doi: 10.1016/j.jbiomech.2004.03.002.
The two major problems that have been reported with the use of polymethylmethacrylate (PMMA) cement are thermal necrosis of surrounding bone due to the high heat generation during polymerisation and chemical necrosis due to unreacted monomer release. Computer models have been used to study the temperature and monomer distribution after cementation. In most of these models, however, polymerisation is modelled as temperature independent and cancellous bone is modelled as a continuum. Such models thus cannot account for the expected important role of the trabecular bone micro-structure. The aim of this study is to investigate the distribution of temperature and monomer leftover at the cancellous bone-cement interface during polymerisation for a realistic trabecular bone-cement micro-structure and realistic temperature-dependent polymerisation kinetics behaviour. A 3-D computer model of a piece of bovine cancellous bone that underwent pressurization with bone-cement was generated using a micro-computed tomography scanner. This geometry was used as the basis for a finite element model and a temperature-dependent problem for bone cement polymerisation kinetics was solved to simulate the bone cement polymerisation process in the vicinity of the interface. The transient temperature field throughout the interface was calculated, along with the polymerisation fraction distribution in the cement domain. The calculations revealed that the tips of the bone trabeculae that are embedded in the cement attain temperatures much higher than the average temperature of the bone volume. A small fraction of the bone (10%) is exposed to temperatures exceeding 70 degrees C, but the exposure time to these high temperatures is limited to 50s. In the region near the bone, the cement polymerisation fraction (about 84%) is less than that in the centre (where it is reaching values of over 96%). An important finding of this study thus is the fact that the bone tissue that is subjected to the highest temperatures is also subjected to high leftover monomer concentration. Furthermore the maximum bone temperature is reached relatively early, when monomer content in the neighbouring cement is still quite high.
使用聚甲基丙烯酸甲酯（PMMA）骨水泥已报道的两个主要问题是，聚合过程中产生的高热量导致周围骨组织热坏死，以及未反应单体释放导致的化学坏死。计算机模型已被用于研究骨水泥植入后的温度和单体分布。然而，在大多数这些模型中，聚合被模拟为与温度无关，松质骨被模拟为连续介质。因此，此类模型无法解释小梁骨微观结构预期的重要作用。本研究的目的是针对实际的小梁骨-骨水泥微观结构和实际的温度依赖性聚合动力学行为，研究聚合过程中松质骨-骨水泥界面处的温度和残留单体分布。使用微型计算机断层扫描仪生成了一块经骨水泥加压的牛松质骨的三维计算机模型。该几何形状被用作有限元模型的基础，并求解了骨水泥聚合动力学的温度依赖性问题，以模拟界面附近的骨水泥聚合过程。计算了整个界面的瞬态温度场以及水泥区域内的聚合分数分布。计算结果表明，嵌入骨水泥中的骨小梁尖端温度远高于骨体积的平均温度。一小部分骨组织（10%）暴露于超过70摄氏度的温度下，但暴露于这些高温的时间限制在50秒以内。在靠近骨的区域，水泥聚合分数（约84%）低于中心区域（中心区域达到96%以上的值）。因此，本研究的一个重要发现是，承受最高温度的骨组织也承受着高残留单体浓度。此外，当相邻骨水泥中的单体含量仍然相当高时，骨的最高温度相对较早达到。
