This is me thinking out loud. I can be completely wrong about this. I'm not a doctor... yada, yada, yada. I found Judy's question interesting. Here is what comes to mind.
In other contexts you've seen me write about sagittal balance and compensatory curves. Like with the deformation of a lumbar vertebra that starts your spine off at an angle that is far from perpendicular (to the ground), there must be a compensatory curve or your head would not be over your body!
With certain types of fusions, the structure and angles of the fused configruration can be critical. For those with such severe cervical problems that they must be fused from C0 all the way to the thoracic spine, they lose all motion of their heads relative to their bodies. If the angle is too far forward they cannot look up or level without leaning back. The converse would also be true.
You can picture that if you have something that is off by 5 degrees in your cervical spine, it would not be noticed in your posture. If you have something in your lumbar spine that is off by 5 degrees, there will be a compensatory curve that will be relatively small and your posture would not be unusual.
All this brings me to.... if you fuse the entire spine so it is like a straight rod... then a vertebra off by 5 degrees in your c-spine will be no big deal. Tilt one 5 degrees in your lumbar spine, then because of the long fusion, your head will be outside of where your shoulders should be. The longer the distance between your head and your off-kilter vertebra, the larger the offset would be.
I don't know it this is related to your case or not. But, if you had a bunch of short fusions that had normal segments between them, that allows for the needed compensatory curves that will compensate for the structural off-kilteredness. (did I just make up a word?) If you then fuse all the short fused segments into one large fusion, then there is no ability for your spine to compensate for the bad angles below. Is it possible that a part (or parts) of your fusions are out of whack and there was no problem until you could no longer compensate for it?
If you felt like you were falling forward immediately after the last fusion, then my theory would hold water. However, if this feeling is new, I woud be very concerned that something is changing. I don't remember you describing that sensation when we've met. Have you discussed this with your spine surgeon or PM?
Do you have recent A/P and lateral views of your entire spine? (or saggital and coronal MRI or CT?) It would be interesting to discuss them.
All the best,
Mark
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