Sutula L C, Collier J P, Saum K A, Currier B H, Currier J H, Sanford W M, Mayor M B, Wooding R E, Sperling D K, Williams I R
Dartmouth Biomedical Engineering Center, Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA.
Clin Orthop Relat Res. 1995 Oct(319):28-40.
Despite studies to determine their causes, significant variations in polyethylene acetabular component wear rates, radial cracking of component rims, and occasional delamination cannot be explained. A subsurface white band frequently occurs in such damaged components. These damaged components often are gamma sterilized. To date, the origin of the band and its effect on polyethylene chemical and mechanical properties, and hence, clinical performance, have not been confirmed, and correlations between radiation sterilization and clinical wear have not been made. By developing techniques for polyethylene retrieval testing and rating, chemical analysis, and mechanical analysis, this research has determined that gamma sterilization in air alters the chemical and mechanical properties of polyethylene over time, resulting in high subsurface oxidation, reduced ductility, and reduced strength. Gamma sterilization-induced oxidation is found to be most severe in the subsurface region of components, and coincides with zones of significantly reduced strength and ductility. This chemical and mechanical property degradation is time dependent and is not typically visible until after 3 years' postirradiation. The presence of the subsurface white band significantly correlates with clinical cracking and delamination observed in retrieved components. Wear of the retrieved components often is observed to have progressed into this heavily oxidized, weakened, and embrittled zone. A method for accelerated aging shows that irradiating in air causes oxidation damage in polyethylene components that is not seen with other sterilization methods. Modifications of gamma sterilization techniques to minimize this damage are discussed.
尽管开展了多项研究来确定其成因，但聚乙烯髋臼部件磨损率、部件边缘径向开裂以及偶尔出现的分层现象仍存在显著差异，这些差异无法得到解释。在这类受损部件中经常会出现亚表面白色带。这些受损部件通常采用伽马射线灭菌。迄今为止，该白色带的起源及其对聚乙烯化学和机械性能的影响，进而对临床性能的影响尚未得到证实，而且辐射灭菌与临床磨损之间的相关性也未明确。通过开发聚乙烯回收测试与评级、化学分析和机械分析技术，本研究已确定，空气中的伽马射线灭菌会随着时间的推移改变聚乙烯的化学和机械性能，导致亚表面高度氧化、延展性降低和强度减弱。发现伽马射线灭菌引起的氧化在部件的亚表面区域最为严重，且与强度和延展性显著降低的区域一致。这种化学和机械性能的降解与时间相关，通常在辐照后3年才会显现出来。亚表面白色带的存在与回收部件中观察到的临床开裂和分层现象显著相关。回收部件的磨损往往会发展到这个高度氧化、弱化和脆化的区域。一种加速老化的方法表明，在空气中辐照会导致聚乙烯部件出现氧化损伤，而其他灭菌方法则不会出现这种情况。本文还讨论了对伽马射线灭菌技术进行改进以尽量减少这种损伤的方法。
