I also recommend a PT.
If lateral raises and front raises and rear delt flyes (I assume the last) are out, there's not much I can think of. (And these are not 'over the head,' so it sounds pretty restrictive.
Here are some ideas you can talk over with your doctor or a PT:
The only thing I can think of is some resistance work done in a pool or water, like doing the lateral and rear raises with just your head sticking out of the water, with the water both supporting your body and acting as resistance. A-Jock would be able to give you some ideas, perhaps, as she teaches water aerobics.
As for the front delt, if you can do push-ups or any chest work, they will get enough work from that. It's more the lateral delt and rear delt that you have to find something for.
Someone suggested resistance bands. If the PT okays it (I know I'm being redundant, but you really have to get some professional advice here), you could perhaps do lateral raises and rear shoulder work while lying on a step or bench (face up or down for the laterals, with the band under your feet, face down for the rear delt work). Another possibility (do I have to repeat this should be checked out by a medical professional first;-) ?) is to do I/T/Y raises for the rear delt: lying face down on a bench or step, hold light weights in your hands and open them out into the various formations: I (in front of you---they would be 'above your head' if you were standing), T (arms to the side) and Y (arms out at a 45-degree angle. This could put more strain on your lower back than you can handle, though, so (I won't repeat myself, 'cuz you KNOW what I'm about to say!)
Another possible option: there are shoulder machines in gyms that you put your upper arm under and lift up, just to parallel to the floor.
