After an accident that has involved a serious injury it is always a good idea to get a 'fit to fly' chit from your doctor. Some airlines will not fly you without one.
If your arm is put in plaster speak to the doctor about it because there may be some discomfort from the pressurisation. I have seen what could be called a half cast, (backslab, I think it is called), which eases the pressure on the injury.
Hope all goes well.