Lead replaces calcium in the bones causing osteoporosis.
Meth also disolves bones so Gray’s history could explain most of whatever damage he had/is/was. But it’s obvious to us here at the farm that when the two bicycle cops picked him up his legs were already dead. Nobody else seems to see that tho. How his legs got dead would be the question. Maybe the cops ran over him with a bike? doesn’t seem like that would break a neck by itself unless the neck was already weakened by lead, meth whatever.
Bottom line is the dumbass should have taken better care of himself.