Zioupos P.
Department of Materials & Medical Sciences, Cranfield University, Shrivenham SN6 8LA, U.K.
J Microsc. 2001 Feb;201(2):270-278.
Bone matrix accumulates microdamage in the form of microcracks as a result of everyday cyclic loading activities. In two very recent studies, which used conventional histological stains and light microscopy techniques, the amount of this in-vivo microdamage in the cortices of long bones has been shown to increase with age. These articles have suggested that in-vivo microcracks may have an effect on the material properties of the tissue. However, a precise quantitative relationship between the number of microcracks and the mechanical properties of these same bones has not been produced before, and in particular the way the microcracks may affect the stiffness, the strength or possibly the toughness of the tissue. This article presents an examination of the in-vivo microdamage in human bones by the use of laser scanning confocal microscopy, which offers better discrimination and allows examination of the cracks in-situ. Quantification of in-vivo fatigue microcracks was performed by counting the microcrack numerical density and surface density in specimens for which we have previously derived a full set of mechanical properties as a function of age. It is shown that bone microdamage relates more to the toughness (measured by three different measures) of ageing bone tissue than to its stiffness and strength. The result allows us (i) to re-evaluate the fragility of ageing human bone and put more emphasis on its energy-related resistance to fracture than perhaps on its stiffness or strength and also (ii) to understand more fully the causal relationship and interactions between microcracks and tissue toughness.
由于日常的周期性负荷活动，骨基质会以微裂纹的形式积累微损伤。在最近的两项研究中，使用传统组织学染色和光学显微镜技术，已表明长骨皮质中这种体内微损伤的量会随着年龄增长而增加。这些文章表明，体内微裂纹可能会对组织的材料特性产生影响。然而，之前尚未得出微裂纹数量与这些相同骨骼的力学性能之间精确的定量关系，尤其是微裂纹可能影响组织的刚度、强度或韧性的方式。本文通过使用激光扫描共聚焦显微镜对人体骨骼中的体内微损伤进行了研究，该显微镜具有更好的辨别能力，并能对裂纹进行原位检查。通过计算我们之前已得出其作为年龄函数的全套力学性能的标本中的微裂纹数值密度和表面密度，对体内疲劳微裂纹进行了量化。结果表明，骨微损伤与老化骨组织的韧性（通过三种不同测量方法测量）的关系比与其刚度和强度的关系更大。该结果使我们能够（i）重新评估老化人体骨骼的脆性，并更加强调其与能量相关的抗骨折能力，而非其刚度或强度，并且（ii）更全面地理解微裂纹与组织韧性之间的因果关系和相互作用。
