Would a broken arm/leg be more painful in zero gravity? I know it would be painful no matter what, but would zero-gravity make it less painful because the bone wouldn't move as much due to lack of gravity, or would it hurt more because of it just floating around?
Yes, your fracture would still hurt in microgravity. Likely worse.
Pain from a fracture comes from inflammation and soft tissue damage around the fracture, as well as mechanical loading of the broken bone. Periosteum (the tough membrane adherent to the surface of the bone and which forms the attachment point of muscles) is highly innervated with pain sensors. It may be ruptured when the bone is fractured, or it may be dissected away from the bone by hemorrhage. Uninjured bones experience no stretching of the periosteum since it is stuck to the rigid bone. Wiggling a fractured bone puts tension on the torn periosteum. Ouch.
Zero gravity may aid immobilization. A well immobilized fracture hurts less, but it still hurts. Don’t ask me how I know.
Acute inflammation hurts less with elevation, but not the orbital kind of elevation. Gravity can aid drainage and reduce swelling, which reduces pain in injured tissues. That's why you put your foot up after an injury. Zero-g means no gravity so you are stuck with the swelling. Swelling puts tension on that pain-sensitive periostium. I think I'd prefer to have my broken leg treated on the ground.
More of a long comment than an answer - we don't know.
The key to minimizing pain from a broken limb would be making the limb immobile. For a leg that would require the use of a splint as a primary measure and keeping the person still, so they don't move the affected leg, as a secondary measure.
Similarly with a broken arm, a splint would be required. To prevent the affected arm from moving it could be strapped to the torso.
It's been a long time since I watched people float around in space and I stand to be corrected on this, but I have observed a tendency for arms to rise and move out from the body. Such movement would cause a broken arm to potentially be more painful. Muscle movement, associated with bringing the arm down again would increase the pain. Strapping the arm to the torso would prevent such movement.
The other thing we don't know is how muscles operate in low or zero gravity. Are their continuous small movements which are largely unnoticed? If so, such movement around a broken bone could increase pain levels.
The closest widely available thing that we have to floating in space is floating in water. Hydrotherapy is sometimes used for recovery when an athlete has broken a bone.
I also happen have some personal experience of being in water with a broken bone and similar injuries.
- Fractured arm, in a cast, as a child. My memory is a bit hazy but I don't remember this particularly being uncomfortable--in or out of the water--and I used my arm quite a lot. It seems like the cast immobilized the bone enough that once the swelling went down it was perfectly fine. (Note: Fiberglass cast. Not a plaster one.)
- Bone bruises on ribs, pulled back muscle, as an adult, with no immobilization. I went in the pool because it seemed like a good way to relax. It turned out to be a bad idea, do not recommend. If you are laying down on land you pretty much hold still unless you use some significant effort to move yourself. In the water, any tiny twitch moves you quite a lot, as well as currents and stuff moving you. It was really surprising how much worse it was to be in the water, since I thought it was going to be relaxing and nice.
Conclusion: If the injury is immobilized, it will probably be equal to being on Earth. If the injury is not immobilized, it will probably be worse than being on Earth, since any tiny muscle twitch will produce a larger motion of the limb vs gravity holding you still.
That's an awesome question. I have no idea, but I genuinely mean it when I suggest that FRX in microgravity be studied in earnest. Find an ambitious scientist & pitch it to them as a proposal they should write.
Luckily, although I have no idea, that doesn't mean the authors Farahani & DiPietro don't. In their linked paper on wound healing in microgravity, they point out the apparent: microgravity makes inflammation kind of awful (stand on your head/hands for a couple minutes & you'll quickly notice how all your fluids that are usually in your feet/legs are now in your face). They also note, more suprisingly, that many cellular/microbiological injury response pathways are decreased in intensity (with a few increased in intensity). If I am reading through the medical terms correctly, this means you'll probably heal slower from a wound in microgravity, everything else considered, but even the authors say they're basically not sure how it all works together in the end.
Also note that it's well-known that both bones and apparently cartilage lose mass during extended stays in microgravity. I doubt this will directly impact the pain levels during a fracture, but I suspect it certainly would make them more common than otherwise.
In short: not sure, but if I personally had to guess, probably yes, the pain would be worse than on Earth. I doubt it would be much worse, but I wouldn't be surprised if the healing process takes a lot longer/is harder to set right & ends up being an issue for a greater amount of time.
Go ask an orthopedist + neuroscientist team! Get them to write an ISS experiment proposal!