IBMS BoneKEy | Perspective

Mechanisms of bone deformation and fracture

Himadri S Gupta

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DOI:10.1138/20100451

Abstract

The fracture of bone involves deformation and failure at multiple levels, ranging from the nanoscale mineral platelet/tropocollagen molecule interface, through micron-scale lamellae, to crack deflection at mesoscopic osteons. In order to understand the key structural mechanisms contributing both to high toughness in normal bone tissue and its deterioration in osteoporosis, quantitative analysis at length scales ranging from the nanometer scale up to the μm scale must be performed and reconciled. This Perspective reviews key research results from the last few years that have begun to clarify the multiple hierarchical fracture-toughening mechanisms in both healthy and diseased bone. Specifically, at the nanoscale, the existence and importance of a non-collagenous protein phase has been recognized, as well as its possible role in interfibrillar shearing and separation, enhanced fracture strength of the mineral phase due to their small size (∼3-5 nm), and the occurrence of highly heterogeneous deformation at scales below 1 μm. At the same time, it has been found that the maximal toughness of bone is achieved due to mechanisms such as ligament/crack bridging and cement line deflection that operate at the higher-length scale of the whole tissue. This has important implications for osteoporosis, where tissue-level structural changes can reduce fracture toughness. This review concludes that a quantitative link between the now-measured deformation and damage initiation at the fibrillar nanoscale level, and the operative crack-deflection and other mechanisms at higher levels, is both necessary and accessible with current high-resolution structural techniques.

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