Okay so I know the 03 Donny Medic headcanon is super popular, but I just thought of a fun alternative to it.
Looking at 03 canon, weirdly enough, anytime we see the gang hurt that either Splinter, Leatherhead, or Casey seems to be the one moving them around and replacing cloths and what not.
Maybe after season 4 I could see Donny brushed up on his medical stuff, but before then? There seems to be an implication the adults(How old is Leatherhead in 03, cause in Mirage, based on that one Laird drawing he's a teen, and in 2012 he starts out implied young but then is trapped in Dimension X for like 40 years so is def an adult by then???) take care of them instead, which considering how 03 deals with their family and friend dynamics tracks.
Meanwhile, interestingly, Donny has not shown a lot of medical specific knowledge, only things that interact with other concepts such as him recognizing that giant bugs with stingers likely function similar to earth's common bees, wasps, and hornets. However he struggled with actually treating the giant wasp's paralytically effect's on Raph, besides a hope that it too will wear off(Yes there is actual things you can do when stung to help lessen pain and other issues, I've gone through that myself. Stepping on stingers is not a fun experience. Dipping the area in cool water for preventing swelling helps a bit. Though with the turtles being turtles idk if that'll work. I mean they where doing the cold rag over forehead treatment on unconscious Leo at the farm house so maybe???)
Of course if you can find a scene pre-season 4 that counters this, fair enough. I just can't think of any scene like that right now.
Not saying they don't exist of course.
I'm also not saying that Donny or the other boys have no medical knowledge, just not the specialized stuff that say 2012 Donnie has(One turtle will collapse from the stress of everything he's doing, but hey at least he can reanimate the dead while making retro-mutagen). Instead I imagine they can do the minor stuff anyone who's taken a first aid class might know.
So what about the adults?
What are their qualifications and experience that led them to learn what Donatello "I want to learn everything" Splinterson didn't yet?
Well for Casey Jones, we know has to have some level of medical knowledge from his own solo vigilante gig pre-meeting the turtles. If he did any actual hockey he might've picked up some stuff there.
Then there's Splinter learned under the Ancient One and clearly knows some of the healing mystical stuff him alongside the Daimyo have.
Lastly Leatherhead was obviously raised in that environment and clearly is shown over and over to have his biochem mutagen degree, we can see that even in Good Genes, though even there he struggles since he did not make Bishop's knock off ooze.
Keeping to 03 themes, rather than one of them doing everything, it's a combination of them all helping.
This also has the fun side effect of Leo during his training under the Ancient One, would likely be the first time anyone besides his dad (or brothers for the minor stuff) would be helping him patch up. After all, we saw what he was fighting while fighting his emotional demons. He would need a patch up after that.
For Leo, it sets in the loneliness being away most likely brought with it. But for the Ancient One? This is his Great Grandturtle, his poor hurt, silly, great grandturtle.
A moment of bonding, but it's painful for both them, and that's not becuase of the physical wounds.
