I don't think there is any 'one size fits all' answer to most spine questions. I've seen literally dozens of adr procedures on completely collapsed disc spaces, including many autofusing segments. There really isn't any 'breaking of the fusion. The annulus and ligaments become more and more calcified, showing the autofusion halo on xray. The more calcified, the less flexible, but it's really not like solid bone and is not immovable (in the cases I've seen.)
These types of surgery require experience, finesse and patience on the surgeons part. It may be much more dangerous to 'brute force' your way to enough disc space to accomodate ADR or fusion cage; but much less dangerous for someone with a lot of experience to carefully release just enough of the annulus and ligaments necessary to achieve the appropriate disc hight, while preserving the necessary stability of the system.
Mark
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