Microdamage formation in individual bovine trabeculae during fatigue testing

Ageing, disease and osteoporosis treatment have been linked to accumulation of microdamage, which is caused by repetitive loading and may eventually causes fatigue failure of bones. Post-hoc investigations for in vivo loading and in vitro experiments have been developed to better understand microdamage formation. In this context, previous studies were not able to discriminate the effects caused by structural changes of the trabecular network from differences of tissue/material properties on microdamage formation. In the present study a fatigue test protocol was established to induce microdamage at a defined tensile stress state of individual trabeculae. Further, a thorough analysis of microdamage analysis was presented for 2D and 3D confocal images, enabling a comparison between the tissue and the mesoscale. Eight individual trabeculae were tested for 1500 cycles, six for 2100 cycles and seven for 3000 cycles (close to failure). Microdamage increased slowly from 1500 to 2100 cycles and showed a rapid increase at 3000 cycles. Diffuse damage was mainly present, although also linear microcracks were visible at 2100 and 3000 cycles. Average microcrack length was 93 mm and diffuse damage density was 4.4% for samples tested for 3000 cycles, comparable to previous studies on trabecular bone cores. Only one to three large microdamage sites were observed in the central region, connected to the trabecular surface with small straight cracks. The presented procedure is a first step to better understand how microdamage formation is influenced by material properties in aged and diseased bone, independently of deteriorated trabecular microarchitecture. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Automated summary

Microdamage accumulation due to repetitive loading can lead to fatigue failure of bones, with studies focusing on understanding its formation through in vivo and in vitro experiments. A fatigue test protocol was established to induce microdamage on individual trabeculae, showing a slow increase up to 2100 cycles and a rapid increase at 3000 cycles. Analysis of microdamage in 2D and 3D images revealed mainly diffuse damage with some linear microcracks visible, offering insights into how material properties influence microdamage in aged and diseased bone.