There must be quite a few CR4's who experience structural failures etc please share it with us..
That is instances where some bones in the skeleton just gave up.
Although I grew up in an area with natural fluoride in the water and thinking that I had high tensile bones in my body I had a lower back fusion (3 level) about 15 years ago.
What did I do wrong? Jumping from a 9m height with a beach umbrella for a parachute. Building a hang glider in +- 1957. (I used a delta wing Avero707?? as inspiration and came up with an almost flying design) The +-50m height test flight was my last, the only visible fracture was a finger. Building a rocket (in response to sputnik) the explosion from the cordite bars taken from rounds of ammunition was a bit to strong for the steel pipe. Rugby etc etc.
The back gradually got worse (pinched nerves and dead legs the lot) until one day when my brain could not make my leg respond to step on the brake. The opp however was a success but I never went back to do my neck.
When you are young you also have good pressure (A girlfriend dad once told me he did not care if I write my name on his lawn, as long if it's not in his daughters handwriting)
Today I can do it in Morse code. The problem is that you must wait for the last e's (dot dot dot)
Other disasters – I am married – I think I had another one but can not remember what it was.