>>> Revision vs. Add-on? I think this is semantics. I'll be making this up as I write. These ideas may not be fully baked. I think that a revision surgery is any procedure that you do after surgery that changes the configuration.
The easiest revision may be a 'clean-up'? After ADR, if a laminotomy or other relatively minor decompression surgery will help, is that a revision? I think if its related to the original procedure, I guess it is.
Bob's question intimates that adding some new hardware represents a different level of surgery than explanting the prosthesis and performing a 360 fusion. Absolutely! Adding Dynesis is a relatively easy surgery compared to the big explant/fuse surgery.
>>> More detail? Remember that each situation that requires a revision is still pretty much a 'one off'. All the revision situations I've been involved with have been completely different situations. In this case, the vertebral body between the 2 prostheses had taken a big tilt. Imagine the foraminal spaces... 2 above and 2 below. 2 will be opened up (upper side a, lower side b) and 2 will be closed down (lower side a, upper side b.) If this progresses to a stage where the exiting nerve roots are being impinged, that will bring leg pain, numbness or other radicular symptoms. Low back pain may also increase... especially facet pain because they are being opened or crunched by the tilt as well.
Typically, myelography would be done to help assess the level of nerve entrapment. (I'm not exactly sure how much can be seen of the exiting nerve roots.) Diagnostic injections can help to isolate problem areas. Again, each situation will be a one-off and the diagnostic process may yield clear positive, clear negative, ambiguous and even conflicting results. In the presence of clear indications, along with clear diagnostics and imaging that all point in the same direction, the decision process will be easy and the confidence in the surgery will be high.
>>> I don't think that this procedure was a shot in the dark. It was based on pretty clear indications. I believe that the surgical decision for revision is much the same as it should be for the original surgery. "Do the lease invasive procedure that stands a good chance of a positive outcome." Easier said than done... especially when indications are less than crystal clear. No surgery based on wishful thinking. I think that the bar is higher and it's harder to pull the trigger on a revision. You are likely to have lower confidence in the surgery, along with a greater (and healthy) relucatance to do more surgery.
>>> I hit a lot of this question in the second bullet above. In this case, the cause of the numbness in legs was clear... the surgery was all about resolving the tilt, decompressing the exiting nerve roots that were clearly being compressed because of the tilt.
I caution everyone to realize that we do not yet know the long-term outcome here. It looks great a 2-weeks out, but that is not what we are after... it's all about long-term results.
Mark
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