When speaking about something that usually moves but now cannot, which word is better: Immobile or Stationary?
I would use the past participial adjective, immobilized, to indicate that something has happened to the thing that has taken away its former mobility. Neither stationary nor immobile conveys that meaning.
P.S. The word immobilized is silent with respect to whether that which has been immobilized will ever be mobile again, but neither does it imply permanence. You would need to say temporarily immobilized or something along those lines if you wanted to indicate that the mobility has been taken away but not permanently. Of course context could also make that clear.
With the patient immobilized, the surgical procedure can proceed.
There are two main meanings that these two words represent. The first definition is "can't move". The second definition is "isn't moving now".
So simply put, it's your choice. I would probably use "immobile", myself.