High-Speed Photography of Human Trabecular Bone during Compression
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High-Speed Photography of Human Trabecular Bone during Compression Philipp J. Thurner1, Blake Erikson1, Zachary Schriock1, John Langan2, Jeff Scott2, Maria Zhao2, Georg E. Fantner1, Patricia Turner1, Johannes H. Kindt1, Georg Schitter1, Paul K. Hansma1 1 2
University of California Santa Barbara, Santa Barbara, CA, USA Computational Sensors Corp., Santa Barbara, CA, USA
ABSTRACT The mechanical properties of healthy and diseased bone tissue are extensively studied in mechanical tests. Most of this research is motivated by the immense costs of health care and social impacts due to osteoporosis in post-menopausal women and the aged. Osteoporosis results in bone loss and change of trabecular architecture, causing a decrease in bone strength. To address the problem of assessing local failure behavior of bone, we combined mechanical compression testing of trabecular bone samples with high-speed photography. In this exploratory study, we investigated healthy, osteoarthritic, and osteoporotic human vertebral trabecular bone compressed at high strain rates simulating conditions experienced in individuals during falls. Apparent strains were found to translate to a broad range of local strains. Moreover, strained trabeculae were seen to whiten with increasing strain. We hypothesize that the effect seen is due to microcrack formation in these areas, similar to stress whitening seen in synthetic polymers. From the results of a motion energy filter applied to the recorded movies, we saw that the whitened areas are, presumably, also of high deformation. We believe that this method will allow further insights into bone failure mechanisms, and help toward a better understanding of the processes involved in bone failure.
INTRODUCTION Mechanical testing of trabecular bone is a vast experimental field1, mainly motivated by the cost and social impact of osteoporosis, a systemic, skeletal disease2, which comes with a reduction of bone strength and a concomitant increase of fracture risk. Trabecular bone is situated at the end of the long bones and in the spinal column, where it fills all of the inner vertebral space. In the long bones it transfers loads from joint faces onto the midshaft of the bone; in lumbar vertebrae, trabecular bone carries and transfers about 90% of the applied load. Thus a change in trabecular bone quality can have a huge impact on strength and on fracture risk in vertebrae. Standard mechanical tests deliver, however, only integral information on a bone sample and no information of local processes experienced in the elastic, yield, and post-yield region. In order to close this gap, experiments have been devised to combine mechanical testing and imaging of trabecular and also cortical bone3,4,5,6,7. Most of these approaches deliver 3D information. However, they all are somewhat time consuming and thus limited to quasi-static testing and/or recording of only a few different states of a sample subjected to mechanical testing. In contrast high-speed photography is designed to record very fast processes, which
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