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The human skeleton comprises two different forms of bone.
- Cortical, or compact bone, accounts for about 80%
of the total skeletal mass and is located primarily in the peripheral skeleton.
- Trabecular, or spongy bone, constitutes some 70% of the axial or
central skeleton, and is visualised as a honeycomb of vertical and
horizontal bars called trabeculae. It is within this region that human red marrow
is almost exclusively located.
Because of these differences, the surface-to-volume ratio is much higher in trabecular
than cortical bone and accordingly bone remodelling has a greater effect on trabecular
bone. Thus bone remodelling, the process which replaces old bone with new has an annual
turnover rate of about 25% in trabecular and 2-3% in cortical bone.
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