Hi Yarnwench,
It is difficult and frustrating when the beauracracy of the insurance game gets in the way of you getting the best care for your condition. There is some information on this site that you might find helpful.
First, here is an overview of spondyloisthesis. According to the treatment section in this overview, the surgeries available have some serious rammifications. For instance, complications listed are:
* compression and temporary/permanent damage of spinal nerve roots, which may cause sensation changes, weakness, or paralysis of the legs. * chronic back pain
This may be some of the reason your insurance is refusing to cover the surgery. There is an interesting video here about how to get the insurance companies to cover anti pain devices. While you are not talking about getting the pump or a neuro stimulator, you might find the advice in this video helpful.
I hope this helps somewhat. Please stay in touch and let us know how you are doing!Vicki M