Hi, Kristin! I am so sorry to hear of your son's injury! We are all sending him tons of pixie dust for quick healing so he can enjoy his
Incredible Summer. I can understand your worry, as my daughter just broke her arm yesterday afternoon. We have a Walt Disney World Resort vacation coming up in a few weeks, so I did a bit of research this morning for both of our families.
I am not sure the type of cast your son is in and if he has any limitations in movement, but there are only three attractions I can find that may be of issue. Avatar Flight of Passage requires riders to sit forward in the ride vehicle, with the chest flush against the vehicle and arms stretched forward (imagine how you would ride a motorcycle). You can do a web search for "Avatar Flight of Passage ride vehicle" to see how this works, and he can also test out a ride vehicle just outside the attraction. Rock 'n' Roller Coaster Starring Aerosmith and Mission: SPACE may be an issue for him due to the type of safety harness they use. All other attractions use safety belts and harnesses that should not be impacted by the cast in any way.
You will want to let his comfort be your guide in deciding if he should ride an attraction. You can also discuss with the Cast Member at the entrance of each attraction to see if there are any restrictions on riding with his type of cast.
Yesterday, the ER physician raised a point to me that I think is of the utmost importance for you and your son. I want to encourage you to talk with your son's orthopedic physician or general physician before your trip. There may be some issues with the nature of his fracture that the physician may want to discuss with you.
I hope this helps you plan a pixie-dusted adventure for your family! Please stop by again if you think of specific questions, so we can help him have the most comfortable and magical trip ever.
Brandy