“There is a genetic disease called fibrodisplaysia ossificans progresiva. When tissue is damaged, it is replaced with bone. Growths form underneath their skin and their joints lock solid So over time those affected slowly become encased in a prison of bone just beneath their own skin.”
If this is the first you've heard of this kind of behavior, study some history. This atrocity has been common for many thousands of years.
We never would have known.