Investigation of the failure behaviour of vertebral trabecular architectures under uni-axial compression and wedge action loading conditions

Vertebral wedge fractures are associated with combined compression and flexure loading and are the most common fracture type for human vertebrae. In this study, rapid prototype (RP) biomodels of human vertebral trabecular bone were mechanically tested under uni-axial compression loading and also under wedge action loading (combination of compression and flexure loading) to investigate the mode of failure and the ultimate loads that could be sustained under these different loading conditions. Two types of trabecular bone models were manufactured and tested: baseline models which were directly derived from μCT scans of human thoracic vertebrae, and osteoporotic models which were generated from the baseline models using a custom-developed bone loss algorithm. The ultimate load for each model under compression and wedge action loading was determined and a video was recorded of each test so that failure mechanisms could be evaluated. The results of the RP model mechanical tests showed that the ultimate loads that could be supported by vertebral trabecular architectures under wedge action loading were less than those that could be supported under uni-axial compression loading by up to 26%. Also, the percentage reduction in strength from the baseline value due to osteoporotic bone loss was slightly less for the wedge action loading compared to uni-axial compression loading. Analysis of the videos for each test revealed that failure occurred in localised regions of the trabecular structure due to bending and buckling of thin vertical struts. These results suggest that vertebral trabecular bone is more susceptible to failure from wedge action loading compared to uni-axial compression loading, although this effect is not exacerbated by osteoporotic bone loss.