Had bone graft fusion of L4, L5, S1 in '83 due to unstable spondylolisthesis. Has been fine since. After recent bout of sciatica, I had X-rays that show degenerative retrolisthesis at L4-L5 of 0.3 cm. It is unchanged on neutral, flexion and extension of views. Question: If L4-S1 is fused solidly, how can L4 -L5 move at all when this section is fused to S1? And what does that mean? My doctor did not inform me of the retrolisthesis; I discovered it after I saw the radiologist report. My doctor only said, "Your fusion is fine." Thanks.