Damage type and strain mode associations in human compact bone bending fatigue

Abstract

When compact bone is subjected to fatigue loading, it develops matrix microdamage, which reduces the tissue's ability to resist fracture. The relative influence of different strain modes on damage and strength in compact bone has not been characterized, to our knowledge. In this study, the nonuniform strain field produced by four-point bending was used to introduce fatigue damage into tibial bending beam specimens from men 40-49 years old. The specimens were then bulk-stained with basic fuchsin to mark damage surfaces and were examined histologically and with confocal microscopy to describe damage morphologies and position relative to tension and compression-strained regions of the specimen. Histomorphometric methods were used to quantify the amounts of different types of bone microdamage. Three major types were observed. In regions subjected to tensile strains, the bone had focal regions of diffusely increased basic fuchsin staining (i.e., diffuse microdamage). Confocal microscopy of these regions showed them to be composed of extensive networks of fine, ultrastructural-level cracks. In compressive strain regions, the tissue developed linear microcracks in interstitial areas similar to those originally described by Frost. Fine, tearing-type (wispy-appearing) cracks were observed near and in the plane of the neutral axis. The paths of these fine cracks were not influenced by microstructural boundaries. Other minor damage morphologies (sector-stained osteons, delamination of regions of lamellae, and intraosteonal cracking) were observed, but their distribution was unrelated to local strain field. Thus. in fatigue of human compact bone, the principal mechanisms of matrix failure (i.e., linear microcrack, diffuse damage foci, and tearing-type damage) are strongly dependent on local strain type.

Dilatational band formation in bone

“…2 B and C) of bone fracture in controlled crack propagation studies show the presence of diffuse damage on the crack path and within the uncracked ligament. Diffuse damage (DD), as we and others have previously reported (9,(24)(25)(26)(27), forms under tensile loading and is characterized by several submicroscopic cracks. Unlike linear microcracks (LM), examination of diffuse damage patches under high-resolution laser confocal, atomic force, and scanning electron microscopy shows the formation of dilatational bands (Fig.…”

Variability and anisotropy of mechanical behavior of cortical bone in tension and compression

“…Different damage mechanisms associated with tension and compression also affect the load-bearing capacity. In tension, a diffused microcrack mechanism was reported in the literature, while linear, cross-hatched microcracks were reported in the region under compression (Boyce et al, 1998). With more energy dissipated in cross-hatch damage than in diffuse damage (Nyman et al, 2009), more energy is needed in compression to generate new crack surfaces than in tension.…”

Micro-scale modelling of bovine cortical bone fracture: Analysis of crack propagation and microstructure using X-FEM

“…Microdamage can be repaired by remodelling process, however, if the bone's repair mechanism is deficient, fragility fractures may result due to minor trauma, especially for ageing bone [10]. Experimentally, both damage location and morphology in the form of linear microcracks were characterised [11][12][13]. Also, the relationship between the crack length and propagation in compact bone tested in cyclic fatigue under four-point bending was investigated [10].…”