In the field of biomechanics, mathematical models are often used to indirectly compute material properties from test results of intact structures. Traditionally, these models have been limited to simple structures such as column, beams, and tubes. In the last few years, the advent of large-scale computer methods in computational mechanics, combined with automated voxel-based meshing techniques based on microtomographic datasets, have made it possible to expand this approach to the determination of tissue or constituent material properties for large-pore foams such as cancellous or spongy bone. The investigator proposes to quantify the accuracy of this approach using a porous mechanical analogue to cancellous bone. The analogues are made of a thermoplastic material which has been treated with an additive to make it x-ray absorptive. Voids are produced by including paraffin beads with the material as it is formed, which are later melted and removed. High resolution Micro-CT scans will be made of the analogues, and voxel-based finite element (FE) models prepared from the resulting data. When combined with direct mechanical testing of each sample, the FE models allow the constituent stiffness to be computed indirectly by an optimization procedure. The predicted stiffness can then be compared with the known stiffness of the void-free plastic as a measure for the accuracy of the method. Although this novel combination of cutting-edge technology from two distinct fields (FE analysis and Micro-CT) holds great promise, this approach is totally untested and no quantification of its accuracy has ever been attempted. The investigators suggest that if the technique can be validated, it will have an enormous impact in the field of orthopaedics, in general and as the study of large-pore size foams, in particular.
