Total bummer! That does explain the unusual presentation of the x-rays though. As for leg raises I should say that in general i am not a fan of the exercise perse as most people don't have enough abdominal control to prevent them from injuring the lumbar spine. But in your case I suppose a few to keep the quads a little active. But then that is mainly rectus femore and the other three are not going to work that much as they aren't involved in hip flexion. Maybe doing this type of movement in standing (think of a ballet class at the barre and you'll get the drift) as well as leg abduction (lifting to the side) when lying on your good side. There are a few variations of that such as doing them with the leg rotated inwards to maintain some gluteal function while you're waiting to be able to weight bear. Even in a fixed brace your physio may be able to do some gentle muscle stimulation to keep the quads active. I have used that before and have even drilled holes into a plaster to make room for a few electrodes. So long at the contractions are not to great this is a usful way to keep the twitch responses active in the quads. Let us know how you get on.