If you consider the statistics - I suppose there are some listed somewhere ... the chance of him getting RSD is probably quite rare.
If it was more common then RSD wouldn't be so unknown to many drs.

But I know as a mom too , we all worry when our kids have to have surgeries.

Is he home near you or still in the service or VA hospital?

Could get his MRIs to someone in your family to look at before the surgery?
Has he had second /third opinions from other MDs yet?

Prayers for your family