It would be interesting to hear what an orthopedic surgeon associated with the second ACL tear had to say about the structure of the knee or Penix's overall lower body bone structure as well as his evaluation of the first surgery/rehab. It is well known that a lot of knee injuries, particularly in women athletes, has to do with structural issues. So does his bone structure indicate potential for injury? Second, usually after in initial ACL tear, most injuries heal and are, in fact, stronger than before. Why didn't that happen with Penix? I too think the Penix injuries seem to be flukes, the S-C problem seems rare. Of his issues, the S-C issue would best be prevented by building upper body strength, which I think he did after 2019. It is quite possible that the injuries Penix has had are it. He might have great durability from now on.
Rex Grossman with the Bears had a string of injuries which ended and he was healthy after that never really having another serious injury iirc. Of course he wasn't a very good NFL quarterback, but he wasn't before the injuries either.