Oh dear, unkyUb, you have been in the wars.
A new set of knees will open a whole new world for you.
I know that at one time, they were reluctant to perform the knee transplant on younger patients as the materials used in the artificial knee were prone to wear out, and the technique of inserting them was such that once done, the operation could not be repeated. Thus, it was used only on older folks in the hope that the knee/operation would last their lifetime.
Things have changed now, and I believe that both the operation and the materials are now such that a re-transplant is probably not required and that if it is, it can be redone succesfully.
Go for it.
I suppose that the nerves to your legs and feet have got themselves all mangled up in your spine.........again, nowadays they can ususally sort that out without too much difficulty.
Lose weight......
...........I suppose your four-legged mobile food disposal unit is quite cheered up at the thought of all the extra goodies that may come his way..
Look after yourself.......it will all get sorted out in good time..