I have severe muscle stiffness in my RSD foot. My foot is constantly rotated to the side at a 45 degree angle and does not move - it stays like that ALL the time. I have been diagnosed with Dystonia, which I was told can often go hand in hand with RSD and is caused by a severe muscle spasm.
I've tried numerous different treatments for it, nothing has worked. My foots been like this 7 years now and as you can imagine, it is VERY painful and has also caused muscle issues.
The thing my PT advised was to not do too much, but also not do too little. I was told that trying to reinforce "normal" behaviour can help BUT I do find when I do too much the rotation and spasm becomes worse.
Another thing you could possibly look into is mirror therapy when you have the stiffness. You do movements with your good limb and that should try and "trick" the limb you are having issues with into working properly. It didn't work for me but everyone is different.
I know a lot of people have had success with Baclofen for these issues, but again its different for everyone. It didn't help me and gave me bad side effects.
Sorry you are going through this, I know how horrible it is and I hope you can find relief soon.
Alison