Risk factors of revision operation and early revision for adjacent segment degeneration after lumbar fusion surgery: a case-control study.

Postoperative sagittal imbalance, including significant PI-LL and C7-S1 SVA were risk factors for revision operation for ASD but not for early revision. These factors are likely to affect the long-term risk of revision operation due to ASD and thus are not considered risk factors for early revision. Narrow DSH of the proximal adjacent level increased the risks of both revision and early revision surgeries. Moreover, old age and a significant number of levels fused further increased the risk for early revision for ASD.