Elastic full-field strain analysis and microdamage progression in the vertebral body from digital volume correlation

The strain distribution in vertebral body has been measured in vitro in the elastic regime but only on the bone surface by means of strain gauges and digital image correlation. Digital volume correlation (DVC) based on micro-computed tomography (micro-CT) images allowed measurements of the internal strain distribution in bone at both tissue (trabecular and cortical bone) and organ (vertebra) levels. However, DVC has been mainly used to investigate failure of the vertebral body but has not yet been deployed to investigate the internal strain distribution in the elastic regime. The aim of this study was to investigate strain in the elastic regime and up to failure inside the vertebral body, including analysis of strain in all directions. Three porcine thoracic vertebrae were loaded in a step-wise fashion at increasing steps of compression (5, 10 and 15%). Micro-CT images were acquired at each step of compression. DVC successfully provided the internal strain distribution both in the elastic regime and up to failure. Micro-CT images successfully identified regions of failure initiation and progression, which were well quantified by DVC-computed strains. Interestingly, the same regions where failure eventually occurred experienced the largest strain magnitude also for the lowest degrees of compression (yet in the elastic regime).