Radio-translucent 3-axis mechanical testing rig for the spine in micro-CT.

To date, no apparatus has yet been devised which would allow the study of bone microstructure of the whole vertebrae under mechanical loading. This paper outlines the design and development of a 3-axis radio-translucent mechanical testing rig for spinal research and testing. This rig is to be used in conjunction with a Shimadzu micro-CT scanner. Several tests were conducted to verify the feasibility of the rig design. First, the maximum range of deformation in compression, flexion\extension, and lateral bending that could be exerted on a goat lumbar functional spinal unit was evaluated using the noncontact digital markers method. Stepwise compression loading was also conducted on a single porcine vertebra and the loading data was compared to results obtained from an industrial grade compression testing machine. Finally, micro-CT scans of a porcine vertebra prior to and at a compression failure strain were obtained. The rig was confirmed to be able to exert pure moment loading in the above mentioned modes of deformation and the extent of deformation was comparable to previous documented results. The stepwise compression loading conducted in the rig was also found to effectively approximate a continuous loading of the same specimen in an industrial grade compression testing machine. Finally, resultant micro-CT images of isotropic resolution 32.80 mum of a porcine vertebra loaded in the rig were obtained. For the first time, trabecular microarchitecture detail of a whole vertebra buckling under 12.1% failure compression strain loading was studied using voxel-data visualization software. These initial series of tests verify the feasibility of the rig as an apparatus incorporating spinal testing and imaging.