Having worked in insurance, and in one of the BCBS in the past, it sounds like their Medical Policy/Utilization unit is really making this decision. I would recommend that you build a very strong case against them, not through your appeals, but through letters and requests from your physicians. Make the medical case really strong as to why he needs the surgery. If he can not walk or sit then he's not working? So show how the lack of surgery is a detriment to your quality of life. Again, if you can get the doctors to make the case for you then it's stronger. Also, consider, how did the injury happen? if it happened at work, then it should be covered under worker's compensation right? Might be time to get a free consultation from a local lawyer as to what your next steps could be.
My guess is that your BCBS insurance will make him go through the cheapest path first, i.e. doctor visits and physical therapy, until that is exhausted they may never cover the surgery. Hope this helps.