Adjacent segment disk degeneration three decades after fusion without attempted reduction for high-grade isthmic spondylolisthesis

Study design Observational study. Objectives To evaluate adjacent segment disk degeneration (ASD) after fusion without attempted reduction at a young age for high-grade isthmic spondylolisthesis. Summary of background data The clinical relevance of ASD remains unclear. Previous studies have shown that spinal fusion is associated with increased ASD but without influence on clinical outcome. Since high-grade spondylolisthesis is a severe kyphotic deformity, one could hypothesize that fusion without attempted reduction in young patients leads to accelerated adjacent segment disk degeneration in adult life. Methods Anterior and posterior disk heights were evaluated on supine radiographs of the spine 8 years and 29 years after fusion without attempted reduction for high-grade spondylolisthesis and also on standing radiographs 8 years and 33 years after surgery. Pelvic parameters were evaluated on standing radiographs obtained 33 years after surgery. Health-related quality of life was evaluated with the Scoliosis Research Society (SRS)-22r questionnaire. Results One segment above fusion the anterior disk height significantly decreased on standing radiographs. Two segments above the fusion, the anterior disk height significantly decreased on supine as well as on standing radiographs. The largest reduction was found two segments above the fusion where the disk height was reduced from 33 to 28% of anterior vertebral height between the measurements at mean 8 years and mean 33 years after surgery. There were no statistically significant decreases in posterior disk heights in any measurement. The disk height showed a moderate negative correlation to PT. There was no correlation between disk height reduction and SRS-22r outcome. Conclusions In our long-term follow-up of fusion without attempted reduction for high-grade spondylolisthesis in young patients, we found only a minor but statistically significant reduction in adjacent segment disk height which had no apparent impact on clinical outcome. Level of evidence Level IV.