I'm really sorry to hear what your son and you have been through
As you are with Shriners anyway, you might want to contact Dr Randall Betz (I think he's at the Philadelphia one? I'll have to double check), as he has been leading a treatment method called the titanium rib. It's not suitable for all children of course, but as it is a type of growth rod, and so can put off further fusion while the spine is allowed to continue to grow, it could be well worth finding out. Also, if as one hopes surgery of any kind can be avoided, I expect that he or his office will be able to offer you useful advice on what alternative treatment could be pursued, what sort of brace might be best if bracing needs to continue/resume etc
I'm really sorry for the circumstances that have brought you here, but nevertheless
Diagnosed at 15 with 50° curve, but probably juvenile IS. Fused in kyphosis (by non-specialised ortho) with a/p surgery T10-L2 @ 21, posterior only revision surgery to correct kyphosis @ 29. Now 38 with further revision surgery and extension of fusion to sacrum required to correct residual kyphosis, restore lordosis and address spinal stenosis.