Why does osteoporosis cause brittle bones?

I have memory of childhood experiments in which eggs and chicken bones were immersed in vinegar for a while (days?), dissolving the calcium. In the case of the egg, the shell would dissolve completely, leaving behind the soft, pliable interior membrane. In the case of the bone, the removal of the calcium left the bone with a rubbery, flexible structure; you could bend it 90 degrees without breaking it.

So, with that in mind, why does osteoporosis - a condition in which one’s bones are short on calcium - increase the probability of fractures? Why aren’t sufferers plagued instead by rubbery bones that bend to all kinds of weird angles without any breakage at all?

It’s not just the calcium that’s missing in osteoporosis. It’s entire bone cells, other minerals, etc…basically, everything that makes up the surface of the bone is missing.

Not to mention that in those experiments, a LOT of the calcium was removed from a large area of the bones. In osteoporosis, small little spots here and there are just at a lower density of bone, meaning there is still calcium, cells, a protein matrix, etc…there is just less of it.

A better analgy than your experiment would be to drill a lot of really tiny holes in a piece of lumbar and see how well is supports a load.

Basically, what bouv said.

Remember that in osteoporosis the bone is normally mineralized. This is not the same as saying the bones are normal. There is just not enough of this normally mineralized bone tissue in the bones of someone with osteoporosis.

As the others have said, osteoporosis is really not the same as soaking a chicken bone in vinegar…

… but, imagine that you take the chicken bone out a quarter of the way to rubber mode. At this point, it will be weaker, but not yet flexible. It will break very easily. So even if osteoporosis was the same as the chicken bone experiment, a person would die long before anything became flexible enough to not break.

To go along with your chicken bone analogy better, you could try to compare that to Osteogenesis imperfecta. That’s the one with no collage throughout the bones evenly, and causes increase fractures and such, with the most severe forms simply having the fetus die in the womb, or within a few days of birth due to the severity of the fractures.

Osteoporosis leaves the bones porous. There is less structure to bones, so they break more easily.