Surgeries that very effectively decompress the offended nervers are more effective at dealing with the radiculopathy associated with nerve compression. Wide laminectomies in which the posterior elements are removed are effective, but they also destablize the area. Typical decompression surgeries are trade-offs between how much they decompress vs. how much damage and destabilization they do.
With fusion surgeries, they have more license to do more decompression because when motion is halted extra structural support is added, they don't have to worry about destabilizing the system.
IMHO, the reason that they are are SOMETIMES not so hot for back pain are for 2 reasons. First is collateral damage from the surgery... big invasive surgery... especially big open posterior surgeries. The second is that most of us (especially those needing multi-level surgery) have multi-focal problems. The fusion will tend to overload the adjacent levels, accellerating degeneration and amplifying pain generators.
I don't think the annulus is in play here. Even in a posterior only fusion with the annulus left intact; once the system is immobilized the annulus will not be loaded substantially. In a 360 or anterior fusion, the posterior annulus will likely be removed or completely unloaded/immobilized.
John's point that 'one size doesn't fit all' is important. There are so many things that can go wrong and any of them can ruin our lives. Unfortunately, we often don't know which issues are important to us unless we are on the wrong side of a failed surgery.
Mark
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