the design for bone-implant systems, it is important to study the mechanical properties of trabecular bone as a function of variables such as anatomic site, bone density, and age related issues. Mechanical factors including modulus, uniaxial strength, and fatigue properties are must be taken into account. Typically, the porosity percent of trabecular bone is in the range 75–95% and the density ranges from 0.2 to 0.8 g/cm3. It is noted that the porosity can reduce the strength of the bone, but also reduce its weight. The porosity and the manner that porosity is structured affect the strength of material. Thus, the micro structure of trabecular bone is typically oriented and ''grain'' of porosity is aligned in a direction at which mechanical stiffness and strength are greatest. Because of the microstructural directionality, the mechanical properties of trabecular bone are highly an-isotropic. The range of young's modulus for trabecular bone is 800 to 14,000 MPa and the strength of failure is 1 to 100 MPa. As mentioned above, the mechanical properties of trabecular bone are very sensitive to apparent density. The relationship between modulus of trabecular bone and its apparent density was demonstrated by Carter and Hayes in 1976. The resulting equation states: where represents the modulus of trabecular bone in any loading direction, represents the apparent density, and and are constants depending on the architecture of tissue. Using scanning electron microscopy, it was found that the variation in trabecular architecture with different anatomic sites lead to different modulus. To understand structure-anisotropy and material property relations, one must correlate the measured mechanical properties of anisotropic trabecular specimens with the stereological descriptions of their architecture. The compressive strength of trabecular bone is also very important because it is believed that the inside failure of trabecular bone arise from compressive stress. On the stress-strain curves for both trabecular bone and cortical bone with different apparent density, there are three stages in stress-strain curve. The first is the linear region where individual trabecula bend and compress as the bulk tissue is compressed. The second stage occurs after yielding, where trabecular bonds start to fracture, and the final stage is the stiffening stage. Typically, lower density trabecular areas offer more deformed staging before stiffening than higher density specimens. In summary, trabecular bone is very compliant and heterogeneous. The heterogeneous character makes it difficult to summarize the general mechanical properties for trabecular bone. High porosity makes trabecular