Direct perfusion measurements of cancellous bone anisotropic permeability

More extensive characterization of trabecular connectivity and intertrabecular space will be instrumental in understanding disease states and designing engineered bone. This project presents an experimental protocol to define the directional dependence of transport properties as measured from healthy cancellous bone when considered as a biologic, porous medium. In the initial design phases, mature bovine bone was harvested from the femoral neck (n = 6 cylinders) and distal condyle (n = 4 cubes) regions and used for 'proof of concept' experimentation. A power study on those results led to the presented work on 20 cubic samples (mean volume = 4.09 cm³) harvested from a single bovine distal femur. Anisotropic intrinsic permeabilities (k_i) were quantified along the orthogonal anatomic axes (i = medial-lateral, anterior-posterior, and superior-inferior) from each individual cubic bone sample. Using direct perfusion measurements, permeability was calculated based upon Darcy's Law describing flow through porous media. The maximum mean value was associated with the superior-inferior orientation (4.65 × 10^-10 m²) in comparison with the mean anterior-posterior (4.52 × 10^-10 m²) and medial-lateral (2.33 × 10^-10 m²) direction values. The results demonstrate the anisotropic (p = 0.0143) and heterogeneous (p = 0.0002) nature of the tissue and encourage the ongoing quantification of parameters within the established poroelastic models.