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I'm just a curious layman, so be gentle. I read around that things like the cranial1 and pelvic2 morphology change with age, but I also read seemingly contradictory information that bones are 'completely ossified' around age 25 (can't post a third link for reference) and that's often cited as meaning "done changing."

Wikipedia (my trusty friend) also describes 'bone remodeling' as a lifelong process, yet also describes ossification (not a lifelong process) as a key component.

So I'm confused. What actually changes in terms of bone morphology throughout an adult's life? Does bone tissue continue to form in adults? Do bones "bend" and flatten ever so slightly into new forms? Additional reading would be appreciated as well.

Thanks

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    $\begingroup$ +1 for writing a good question. Somebody competent will answer. $\endgroup$
    – Tyto alba
    May 24, 2017 at 7:26
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    $\begingroup$ The statement " bones are 'completely ossified' around age 25" means that all bones are now osseous i.e. there is no cartilage or membranous present after 25yrs. This doesn't mean that bone resorption and ossification doesn't take place. The term Ossifocation has different meaning in different context. $\endgroup$
    – JM97
    May 24, 2017 at 12:23

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Bone never stops changing.

Your bones are constantly being broken down and reformed on a microscopic level. Your bones are done growing at a certain point but they continue to be reshaped. Remember bone exists to supply calcium (and to a lesser extent phosphorus), to your muscles, Your body needs to break down the surface of the bones for this calcium.* So bone is dissolved and redeposited constantly, this regulated mineral levels but also allows the bone to slowly reshape itself.

Bone will slowly reshape itself to resist any stress it experiences, for instance if you build muscle the attachment point for the muscle will become more rugged to strengthen the attachment. A runner's leg bones will get thicker and denser to resist the greater stresses. Joint surfaces can even reshape with repetitive motion.

*bone originally evolved as armor but this has been lost in modern vertebrates. Vertebrate muscle requires calcium to function, Vertebrates have lost the armor but not the need for a calcium store, and have repurposed into a structural support. Vertebrates without structural bone need to have massive calcium levels in their body tissue instead.

for continued reading there is a whole series of books by R. Mcneill Alexander that cover bones in fascinating detail.

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    $\begingroup$ "bone exists first and foremost to supply calcium to your muscles" - What makes you so sure of claiming that? Bones certainly did not evolve for this reason. Also see: ncbi.nlm.nih.gov/pmc/articles/PMC3237026 $\endgroup$
    – adjan
    May 24, 2017 at 21:48
  • $\begingroup$ oops that was my bad, forgot to add phosphate, good catch. But if you read carefully that source supports my claim, calcium phosphate is resistant to the acidic conditions produced my active muscles creating a calcium and phosphate store that can be modulated. bone did evolve for that reason. $\endgroup$
    – John
    May 25, 2017 at 10:18
  • $\begingroup$ The structural use of bone (originally armor) could only occurred after the ability to deposit calcium phosphate had evolved. $\endgroup$
    – John
    May 25, 2017 at 10:25
  • $\begingroup$ @john What does 'joint surfaces can even respade' mean? Respade means to turn over(Wikitionary). Please can you explain,what do you mean by the above statement? $\endgroup$
    – AScientist
    May 25, 2017 at 15:57
  • $\begingroup$ dyslexia plus a typo, "reshape" I'll fix that. $\endgroup$
    – John
    May 25, 2017 at 20:15

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