Comparative Mechanical Properties and Histology of Bone

Different bone tissues differ in their amounts of porosity, mineralization,reconstruction, and preferred orientation. All these have important effects on mechanical properties. Very porous, cancellous bone is always weaker and morecompliant than compact bone on a weight for weight basis, yet it occurs in placeswhere its energyabsorbing ability, or its low density, is advantageous. Bonevaries considerably in its mineralization, and such variations have quite disproportionate effects on mechanical properties. These variations can be shown to be adaptive. In particular, there must always be a compromise between stiffnessandresistance to fracture; these two properties run contrary to each other. The reason for secondary remodeling is an unresolved problem, though in a few places the role of such remodeling in changing the grain of the bone is clearly mechanically adaptive. The mechanical properties of non-mammalian bone are obscure, and as the histology of such bone is often quite different from that of mammalian bone, we are no doubt in for some surprises when the mechanical properties ofnonmammalian bone are discovered.