Bone Microdamage and Its Contributions to Fracture
Microdamage formation is a major determinant of bone fracture. The nature and type of damage formed, as linear microcracks or diffuse damage, depends on the interaction between applied loading and the extracellular matrix. Human bone naturally experiences
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Abstract Microdamage formation is a major determinant of bone fracture. The nature and type of damage formed, as linear microcracks or diffuse damage, depends on the interaction between applied loading and the extracellular matrix. Human bone naturally experiences multi-axial cyclic loading. Changes in its extracellular matrix can contribute to the overall deterioration of bone’s mechanical integrity with aging and/or disease. This chapter provides a review of literature reports on the detection of microdamage and its limitations; alterations in microdamage with aging and disease; differences in microdamage between gender and bone’s two distinct structural forms (cancellous and cortical); and the role of microdamage in bone’s mechanical properties.
1 Introduction Microdamage forms in composite materials, such as bone, due to loading and is an indicator of the fracture process and eventual failure of the material. In vivo cyclic loads lead to incremental formation of microdamage through fatigue. The fatigue process results in small cracks that accumulate in the mineralized matrix of bone, which can alter bone’s mechanical properties. Hence, the increased number of cracks combined with further load bearing can result in failure [1, 2]. Although microdamage occurrence is common in many load-bearing materials that are subject to repetitive stresses, bone has the ability to remove microdamage through
L. Karim D. Vashishth (&) Department of Biomedical Engineering, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY, USA e-mail: [email protected]
Stud Mechanobiol Tissue Eng Biomater (2013) 5: 87–104 DOI: 10.1007/8415_2011_107 Ó Springer-Verlag Berlin Heidelberg 2011 Published Online: 20 October 2011
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Fig. 1 Microdamage forms as two different morphologies. An image of a linear microcrack (top) is shown under a bright-field microscopy, and b confocal microscopy. An image of diffuse damage (bottom) is shown under c bright-field microscopy, and d confocal microscopy. Scale bars = 50 lm. Reprinted with permission from Elsevier [8]
a repair process of intracortical remodeling [3–5]. However, there is an age-related accumulation of microdamage in bones [1, 6], due either to deterioration of the repair mechanism with age [4, 7] or to matrix changes that reduce the damage resistance of bone. Microdamage can take two distinct forms [1, 6, 8]. Two damage morphologies, linear microcracks and diffuse damage (Fig. 1), result from different types of applied loading [9–11]. Linear microcracks form primarily due to compressive loading and appear as sharply defined cracks [10, 12, 13]. They are primarily found in the interstitial regions of bone where they follow the lamellar interface and stop at the cement lines of osteons [8, 11, 14]. On the other hand, diffuse damage results from tensile loads [9]. It has the appearance of a spread mesh of submicroscopic cracks [15]. Diffuse damage is closely associated with osteonal regions in bone, and it does not f
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