3D real time studying fatigue microcrack formation in cemented femur construct

描述（由申请人提供）：骨水泥型全髋关节置换术（THA）的失败通常发生在微裂纹合并为临床可观察到的失败时。相当多的研究集中在减少器械柄中的应力应变、骨水泥界面的失效和骨水泥鞘的失效上。然而，目前尚不清楚渐进性微裂纹形成在骨水泥型股骨柄结构疲劳失效中的作用。 我们最近的研究表明，声学签名的模型构造允许分类的疲劳引起的微裂纹分为两种类型。大多数I型微裂纹在具有高信号能量的SEM下是可识别的。II型微裂纹与低信号能量有关。它的形成、积累和 I型微裂纹的分布与试样失效相关，而II型微裂纹似乎与失效相反。 在这方面的调查的下一步是进一步研究这些微裂纹和材料强度之间的相关性，以及疲劳失效机制。为了达到这个目的，我们将采用新发展的声发射微裂纹源定位技术，在以下步骤。(1)我们将描述骨水泥中的微裂纹，并研究它们对骨水泥弯曲强度的影响。 (2)我们将描述股骨柄-骨水泥界面处产生的微裂纹，并研究其对结构剪切强度的影响。(3)我们将使用尸体样本表征骨水泥型股骨柄结构疲劳测试中产生的微裂纹，并将其存在与SEM观察结果相关联。我们将使用定量指标来评估各种疲劳载荷条件下微裂纹的形成和发展。我们将测量这些微裂纹的开始时间、分布、密度和进展。这一目标的实现将增进我们对 股骨结构疲劳失效机制和开放的新方法来研究THA松动。在本文中，我们将检验以下假设： 在临床上可观察到的失效发生之前，两种类型的微裂纹在全髋关节置换术的骨水泥型股骨柄结构中开始。I型微裂纹直接导致股骨柄结构松动。II型微裂纹起到能量吸收器的作用，从而延缓松动过程。

DESCRIPTION (provided by applicant): Failure of cemented total hip arthroplasty (THA) often occurs when microcracks coalesce into a clinically observable failure. Considerable researches have focused on reducing stress risers in the devices' stem, on failures at the cement interfaces, and on failure in the cement mantle. However, it is not clear what role of progressive microcrack formation play in fatigue failure of a cemented femur stem construct. Our recent studies revealed that the acoustic signatures of model construct permit categorization of the fatigue induced microcracks into two types. Most Type I microcracks are identifiable under SEM with high signal energy. Type II microcracks are associated with low signal energy. The formation, accumulation, and distribution of Type I microcracks correlate with specimen failure whereas Type II microcracks seems to have a counter-correlation with failure. The next step forward in this avenue of investigation is to further study the correlation between these microcracks and material strength, and fatigue failure mechanisms. To achieve this objective, we will use newly developed acoustic emission microcrack source location technique in following steps. (1) We will characterize microcracks in bone cement and investigate their effects on the flexural strength of the cement. (2) We will characterize microcracks generated at the stem-cement interface and investigate their effects on the shear strength of the construct. (3) We will characterize microcracks generated in fatigue tests of cemented femur stem construct using cadaver specimens and correlate their presence with SEM observations. We will use quantitative indicators to assess the formation and progression of microcracks under various fatigue loading conditions. We will measure the onset time, distribution, density, and progression of these microcracks. The accomplishment of this objective will enhance our understanding of femur construct fatigue failure mechanism and open novel approaches to the studies of THA loosening. In the proposed work, we will test the following hypothesis: Two types of microcracks initiate in the cemented femoral stem constructs of total hip arthroplasty before clinically observable failure occurs. Type I microcracks directly contribute to the loosening of a femur stem constructs. Type II microcracks function as energy absorbers and thereby retard the loosening process.