So, despite 70 years of forced service under Hydra, and of course the initial torture and conditioning by them which would have obviously included many injuries, Bucky has no scars. The serum accelerated his healing, meaning wounds are usually gone within a few days, and scars, a month tops.
Except for his shoulder.
That would be because it's regularly operated on. Opening up and examining the arm, attaching new anchors to keep it fixed to his bones, updating the wiring connected to his nervous system, etc. Pretty much every time he's taken out of cryo, he's strapped down and torn open. All without the aid of anesthesia, of course, because machines don't feel pain (and the scientists know his metabolism would get rid of it before it did it's job anyway, so why waste it).
Bonus if Steve and/or other Avengers learn about this. And this obviously becomes a problem when Tony and Bruce need to work on his arm to help him.
Bucky, Medical torture and aftermath
Except for his shoulder.
That would be because it's regularly operated on. Opening up and examining the arm, attaching new anchors to keep it fixed to his bones, updating the wiring connected to his nervous system, etc. Pretty much every time he's taken out of cryo, he's strapped down and torn open. All without the aid of anesthesia, of course, because machines don't feel pain (and the scientists know his metabolism would get rid of it before it did it's job anyway, so why waste it).
Bonus if Steve and/or other Avengers learn about this. And this obviously becomes a problem when Tony and Bruce need to work on his arm to help him.