Importance of the integrity of trabecular bone to the relationship between load and deformation of rat femora: an optical metrology study

Bone is a composite hierarchical structure composed of a cortical shell and inner trabecular tissue. One of the most basic questions in whole-bone function is the relative contributions of cortical and trabecular bone tissues to the loaded whole bone. In this study, the manner in which the cortical surfaces of an intact proximal rat femur deform under load is compared to the same femur after some of the trabecular bone in the distal femoral neck was removed. The surface displacements were measured by electronic speckle pattern interferometry (ESPI) and the extent of trabecular bone removed was determined by high resolution micro-CT scanning. The results show that after damaging the trabecular bone tissue in the distal femoral neck, the manner in which compressive loads are transformed to other regions of the femoral neck changed. The whole bone behaved in a 'stiffer' manner. This demonstrates the importance of connectivity of the trabeculae and that beyond a certain threshold of damage the normal load-transferring mechanism is impaired. Since these experiments were carried out in a non-contact non-destructive manner in a wet environment and the rat femur was loaded in a close-to physiological manner, we postulate that our results have a direct relevance to the in vivo biomechanical behavior of the femoral neck.