Jackie,If it was me, I would much prefer a train vs plane for several reasons:
If you get room 'H' or maybe a lower level roomette, you could stretch out/elevate your bum knee/leg, making the ride more comfy. (If you have any trouble getting around, get room "H" rather than a roomette, it has bathroom!)
The Sleeping Car Attendant should take pretty good care of you, including bringing you your meals, etc. Maybe even setting up the lower bed for you during the day, if you need it.
It actually may be more relaxing & better than flying because you would not have to figure out how to prop your leg up if needed, or walk too far for the bathroom.
Years ago I had a broken leg with a cast from hip to toe. I would never had considered flying like that. I have one word that comes to mind- turbulence!
If you're able to navigate stairs, you may want to consider a regular bedroom. They have a complete bathroom w/shower, a sofa you could stretch out on & a chair as well. That may be cheaper than bedroom 'H'.
So, I would say even though it will take more time to get there by train, I think it would be better for your injury & the healing process to take the train. I think it may lower your stress level because it would be so much easier to make you comfortable on the train, vs on the plane where there's alot less space available. So much for my two cents. Hope you heal fast!!!
Sunchaser