I've had many worse cases than "Million Dollar Baby." But if that's what bothers you, don't do that aspect. you get trained in all aspects of PM&R and then get to decide how you want to practice it. We tend to see more chronic than acute patients, and no matter what the disorder/disease/problem, chronic ones have worse outcomes than acute.
Re: "Murderball" - I know a lot of those guys. I used to referee Quad Rugby in the 90's when it was just comnig out of it's infancy as a real sport. I watched it grow from about 20 teams in the nation to 50 - 60, I'm sure it's even more now. Joe Soares was an ******* back then even. The movie shows him to be an even bigger weanie now and a crybaby as well. He was known to argue every call made against him. Sore loser.
I went to school with Kevin Orr (U of Ill). He couldn't play quad rugby since he had no real impairment of the UE's (arthrogryposis), but was world-class in track. Ironically, his twin brother played for the regular/able-bodied rugby team. Kevin's put on some weight since college... In college, he was quite possible the strongest guy in a wheelchair I've ever known. I once watched him race a quad across the gym floor, Kevin out of his wheelchair. The quad was a 2.5 in quad rugby terms (about what Mark Zupan is now), and Kevin dragged himself just with his arms, about as fast as I could run. Kevin won. He could also run/walk handstand-style across the gym floor, his thin legs dangling in the air. Ahh, the memories...
Mark Zupan was injured after I stopped ref'ing (after I started residency), and his story of his injury and rehab/recovery is awesome in it's intensity. You'll meet a lot of people with tales like that in PM&R and in wheelchair sports. Mark is little bit more, how shall we say, intense, than the average quad rugby players, but I've seen worse.
If you ever get the chance, go see quad rugby played live. If you're an MD/DO with rehab experience, you can be a certifier who decides what level (0.5 - 3.5) a player is. There are lots of opportunites to get involved with that and other wheelchair sports. I used to help out with W/C basketball, track and other sports.