Symptomatic Adjacent Segment Degeneration at the L3–4 Level after Fusion Surgery at the L4–5 Level: Evaluation of the Risk Factors and 10-Year Incidence

There have been few studies on revision surgery for clinically symptomatic adjacent segment degeneration (CASD). We aimed to find the incidence of revision surgery due to CASD and to analyze the factors that affected CASD at the L3–4 level after L4–5 or L4–5–S1 level fusion surgery over a long-term follow-up period.