I mean, to me, injury prone should be easily defined. Your body is more prone to sustaining an injury than the average guy.
Two guys have the same (x) impact and one has (y) injury result and the other has (z) non-injury result, then one guy is more injury prone than the other. At least with regard to that part of the body.
So, for me, Gordon is an injury prone guy because he gets banged up everywhere and misses games because of different kinds of impact - many of which other guys' bodies can sustain.
Ryno, meanwhile, had a major injury that any spine would have suffered with that kind of impact at that angle, speed, etc. The ankle/knee injury, I don't know. Maybe some better athletes could have been okay.
But by my definition, I don't consider him injury prone.