[CharlesinCharge]

There is considerable debate about it, but from what I have read the ONLY real advantage of having fusion at L-5/S-1 is that there is only one level that could be affected by Adjacent Segment Disease. At any other level, you have the level above AND the level below that can be affected when you get fused (especially if you are young, as the longer you go the higher the rate of ASD per clinical reports). If you get a fusion at L-5/S-1 you only have the level above. The surgeons I spoke to told me there is still enough motion at that level to make ADR advantageous, and as Kimmers said fusion adds stress to the SI joint. The reports I read said that at 3 years after a fusion the rate of Adjacent Segment Disease was only 15%, but at 10 years out the rate was almost 40%. That is why ADR surgery came along, fusion works great for fixing Degenerative Disc Disease BUT the problem for decades has been ASD. If not for that, ADR surgery might not have been developed.