Compression osteons

Mechanical properties of cancellous (spongy) bone are dependent on the bone density and porosity, and therefore the strength and stiffness of spongy bone is much lower than that of cortical or osteonic bone. The axial compressive strength is related to the square of the bone density. 

Fig. 9.16. Hierarchical structure of adult human bone. Tropocollagen molecules are arranged in a so-called quarter-stagger structure, with platelets of hydroxy apatite in between. The fibres formed by this structure unite to fibre bundles which in turn form lamellae. The major part of the bone consists of osteons made of ring-shaped lamellae. Near the bone s surface, the lamellae are parallel to the surface. The orientation of the fibre bundles within the lamellae depends on the mechanical loads on the bone in tensile regions, they are ahgned in the loading direction as shown in the figure, in compressive regions, the fibre bundles of some lamellae are perpendicular to the loading direction...

---