you may also want to vary the 'cell' size as a function of distance from the bearing surfaces. the cells are smaller towards the boundary surface, and get progressively larger as you reach the marrow portion of the bone. The cells also display a 'radial' orientation, or elongation about the center of rotation of , from your photo, what looks like a hip bone. That said, the cells seem to group into 3 sizes of cells, call them small, medium and large. Depending on how anatomically correct you wish to be, you could model the marrow zones as the long series of tubes that they are, the intermediary cells as ovaloids, and the bearing surface as a small sphere packing surface.