Thayer School of Engineering, Dartmouth College, 8000 Cummings Hall, Hanover, NH 03755, USA.
J Bone Joint Surg Am. 2010 Oct 20;92(14):2409-18. doi: 10.2106/JBJS.I.01006.
Elimination of free radicals to prevent oxidation has played a major role in the development and product differentiation of the latest generation of highly cross-linked ultra-high molecular weight polyethylene bearing materials. In the current study, we (1) examined oxidation in a series of retrieved remelted highly cross-linked ultra-high molecular weight polyethylene bearings from a number of device manufacturers and (2) compared the retrieval results with findings for shelf-stored control specimens. The hypothesis was that radiation-cross-linked remelted ultra-high molecular weight polyethylene would maintain oxidative stability in vivo comparable with the stability during shelf storage and in published laboratory aging tests.
Fifty remelted highly cross-linked ultra-high molecular weight polyethylene acetabular liners and nineteen remelted highly cross-linked ultra-high molecular weight polyethylene tibial inserts were received after retrieval from twenty-one surgeons from across the U.S. Thirty-two of the retrievals had been in vivo for two years or more. Each was measured for oxidation with use of Fourier transform infrared spectroscopy. A control series of remelted highly cross-linked ultra-high molecular weight polyethylene acetabular liners from three manufacturers was analyzed with electron paramagnetic resonance spectroscopy to measure free radical content and with Fourier transform infrared spectroscopy to measure oxidation initially and after eight to nine years of shelf storage in air.
The never-implanted, shelf-aged controls had no measurable free-radical content initially or after eight to nine years of shelf storage. The never-implanted controls showed no increase in oxidation during shelf storage. Oxidation measurements showed measurable oxidation in 22% of the retrieved remelted highly cross-linked liners and inserts after an average of two years in vivo.
Because never-implanted remelted highly cross-linked ultra-high molecular weight polyethylene materials had no measurable free-radical concentration and no increase in oxidation during shelf storage, these materials were expected to be oxidation-resistant in vivo. However, some remelted highly cross-linked ultra-high molecular weight polyethylene retrievals showed measurable oxidation after an average of more than two years in vivo. This apparent departure from widely expected behavior requires continued study of the process of in vivo oxidation of ultra-high molecular weight polyethylene materials.
消除自由基以防止氧化在最新一代高度交联的超高相对分子质量聚乙烯承载体的开发和产品差异化方面发挥了重要作用。在本研究中，我们（1）检查了从多个设备制造商回收的一系列再熔化的高度交联的超高相对分子质量聚乙烯轴承中的氧化情况，（2）并将回收结果与货架存储的对照标本的发现进行了比较。假设是辐射交联再熔化的超高相对分子质量聚乙烯在体内的氧化稳定性将与货架储存期间以及已发表的实验室老化测试中的稳定性相当。
从美国各地的二十一位外科医生处回收了五十个再熔化的高度交联的超高相对分子质量聚乙烯髋臼衬垫和十九个再熔化的高度交联的超高相对分子质量聚乙烯胫骨插入物。其中 32 个回收物已经在体内使用了两年或更长时间。每个都使用傅里叶变换红外光谱法测量氧化程度。对三个制造商的再熔化的高度交联的超高相对分子质量聚乙烯髋臼衬垫的对照系列进行电子顺磁共振波谱法分析以测量自由基含量，并进行傅里叶变换红外光谱法分析以测量最初的氧化程度和在空气中存放八年至九年后的氧化程度。
从未植入的、在货架上存放的对照物在最初或在八年至九年后的货架存放期间均没有可测量的自由基含量。从未植入的对照物在货架储存期间没有显示出氧化增加。在货架储存期间，氧化测量表明在从未植入的对照物中没有发现氧化增加。在体内平均两年后，在 22%的回收再熔化的高度交联衬垫和插入物中观察到可测量的氧化。
由于从未植入的再熔化的高度交联的超高相对分子质量聚乙烯材料没有可测量的自由基浓度，并且在货架储存期间没有氧化增加，因此这些材料预计在体内具有抗氧化性。然而，一些再熔化的高度交联的超高相对分子质量聚乙烯回收物在体内平均两年多后显示出可测量的氧化。这种明显偏离广泛预期的行为需要继续研究超高分子量聚乙烯材料在体内氧化的过程。
