Despite the demonstrated safety and efficacy which several of these devices have displayed, many insurance companies continue with denials, claiming investigational status. This is frankly a bunch of hogwash mainly due to some of the less than positive results of certain lumbar artificial disc surgeries, and the insurance companies' inability to distinguish between the two (one is in the neck, the other in the back). The other possible reason is a lack of superiority data. Because of the high cost of running clinical trials, most device companies prefer to perform "noninferiority trials" instead of "superiority trials" since the former require less statistical power and therefore fewer patients and less money. All trials to date on these devices have been noninferiority trials which gives insurance companies a window for denial.
A recent study by McAfee, et al, in the journal Spine 2012 performed a meta-analysis of the available non-inferiority trials, generating enough numbers to demonstrate significant superiority of artificial cervical disc replacement over fusion. Although the statistics behind this aren't as clean as a larger double-blind controlled trial, this is currently the best evidence we have that artificial cervical disc replacement is a better operation (in the appropriate patients) than ACDF. Below is the link:
This data also completely jibes with my personal experience with this technique. It is quite similar to a fusion in nature so is easy for surgeons to learn, can be performed outpatient, and clinical results are usually excellent. Here is a link to a live video of a cervical disc replacement:
For more information about lumbar and cervical artificial disc replacement: