hello and welcome, you'll find lots of helpful advice and kind words here. i'm sorry to hear about your son. i got RSD in my right ankle when i was only 11 after a surgery and had my surgeon say many of the same things to me.
please help you son to keep his ankle moving, if it is sensitive to touch, start slow with desenitation, a tissue or a cotton bowl. The worst thing for RSD is to not move or use the limb. make sure he is at least getting up with his crutches and move as much as possible. Trust me i know it's painful, but early diagnosis is the key to a recovery. you need to get him in to see a pain management doctor who actually knows RSD. where are you located? There are a few children's hospitals around that have been benefical. if at all possible also find a pt that is fimilar with RSD. as said above NO ICE!!!!