"Matt Whiting" wrote

The artificial disk unit has essentially a partial titanium vertebrate on
each side of the polymer disk. This is glued (maybe also screwed, I don't
know) to the OEM bone vertebrate much the way artificial hips and knees
are put in.

That sounds like a new technology disc, than the ones I looked at a couple
of years ago; they just sat in there, held in by the surrounding soft
tissue. That isn't surprising; medical tech move at a very fast rate.

In this scenario, I'm not sure why they couldn't break apart a fused area,
but maybe it is simply too aggressive a procedure to do with the spinal
cord in the middle.

I would think the amount of bone added in the fusion is the biggest factor.
Basically, all the space that the normal disc occupied, is filled with bone,
now. That would be a lot to remove, especially like you said, right next to
the spinal chord.
--
Jim in NC