Endosteal resorption
What it means
Endosteal resorption is the thinning of bone from the inner surface outward, which widens the hollow space inside the bone as we age.
Understanding this process helps explain why bone strength depends on more than just bone density, and why cortical thickness matters for fracture risk.
Endosteal resorption is the gradual thinning of bone from the inside. The endosteum is the inner surface of your bones, and as we age, bone tissue is removed from this inner surface, which widens the hollow space inside the bone shaft.
At the same time, something else is happening on the outside: the bone's outer diameter slightly increases through periosteal expansion. This is a helpful trade-off, because a wider, hollow tube is actually stronger for its weight than a solid rod of the same material, similar to basic engineering principles. So as the inside hollows out, the outward growth partially makes up for the density being lost.
However, this compensation only goes so far. If the cortical bone, the dense outer shell, becomes too thin, the widened geometry can no longer make up the difference, and the risk of fracture increases more steeply. Understanding this helps explain why both the inside and outside of your bones matter, not just overall density.
How sure is this?
Graded Established Science: Supported by broad scientific consensus and decades of research. Read each study with its grade in mind. One study is a piece of the picture, not the whole of it.
Where the Academy teaches it
This page is the short version. The lessons teach it in full, with the context around it and a quiz to lock it in.
Related words
Periosteal expansion is the slight widening of bone that happens on its outer surface as we age, even as the inside…
Cortical bone is the dense, hard outer layer of bone that forms a protective shell and resists bending and twisting…
Bone remodeling is the lifelong cycle where cells called osteoclasts remove old bone and osteoblasts build new bone…
Osteoclasts are the cells that break down old bone tissue, working alongside bone-building osteoblasts to constantly…
Bone mineral density (BMD) measures how much mineral is packed into your bones, usually estimated with a DEXA scan,…
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