The department of managed health care in california is a regulatory agency for HMO's and they may (under certain circumstances) offer an Independent Medical Review of a case. However, careful review of their cases (you are free to research their decisions using their online databse) shows that they have NEVER approved/overturned a decision by an insurance company to deny coverage of an artificial disc replacement. Having gone down that route w/my fiancee I almost suspect we were enticed by the insurance company to go down that route since they were well aware of the DMHC's position.
Thanks
Here's the link to the website:
http://www.hmohelp.ca.gov/