Furmanski Jevan, Anderson Martin, Bal Sonny, Greenwald A Seth, Halley David, Penenberg Brad, Ries Michael, Pruitt Lisa
Case Western Reserve University, Mechanical and Aerospace Engineering, 414 Glennan, CWRU, 10900 Euclid Ave., Cleveland, OH 44106, USA.
Biomaterials. 2009 Oct;30(29):5572-82. doi: 10.1016/j.biomaterials.2009.07.013. Epub 2009 Jul 29.
Highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is increasingly used as a bearing material in total hip replacements. Cross-linking of UHMWPE has been shown to increase wear resistance but decrease its fracture resistance. We analyzed the clinical fracture failure of four cross-linked UHMWPE total hip replacement components of four different designs via microscopic observation of the fracture surfaces, and found that in all cases fractures initiated at stress concentrations in an unsupported region of the component (termed the elevated rim). Finite element analyses (FEA) of each individual implant design were then conducted. Results from this analysis demonstrated that the predicted magnitude and orientation of maximum principal stress due to mechanical loading of the elevated rim was sufficient to propagate initiated fatigue cracks in each case. FEA also predicted that cracks may arrest after some amount of growth due to a steep stress gradient near the initiation site. Further, while anatomical positioning of the implant and material properties affect the risk of fracture, we examined whether these failures are strongly related to the notched elevated rim design feature that is common to the four failed cases presented here. We believe that cross-linked UHMWPE remains an excellent bearing material for total hip replacements but that designs employing this material should mitigate stress concentrations or other design features that increase the risk of fracture.
高度交联的超高分子量聚乙烯（UHMWPE）越来越多地被用作全髋关节置换中的承重材料。已表明，UHMWPE的交联可提高耐磨性，但会降低其抗断裂性。我们通过对四个不同设计的交联UHMWPE全髋关节置换部件的骨折表面进行微观观察，分析了其临床骨折失效情况，发现在所有病例中，骨折均起始于部件无支撑区域（称为隆起边缘）的应力集中处。然后对每个植入物设计进行了有限元分析（FEA）。该分析结果表明，由于隆起边缘的机械载荷导致的最大主应力的预测大小和方向足以在每种情况下使起始的疲劳裂纹扩展。FEA还预测，由于起始部位附近的陡峭应力梯度，裂纹在一定程度的扩展后可能会停止。此外，虽然植入物的解剖位置和材料特性会影响骨折风险，但我们研究了这些失效是否与这里展示的四个失效病例共有的带缺口隆起边缘设计特征密切相关。我们认为，交联UHMWPE仍然是全髋关节置换的优良承重材料，但采用这种材料的设计应减轻应力集中或其他增加骨折风险的设计特征。
