Spinal fusion on adolescent idiopathic scoliosis patients with the level of L4 or lower can increase lumbar disc degeneration with sagittal imbalance 35 years after surgery

INTRODUCTION: The purpose of this study was to investigate the long-term incidence of lumbar disc degeneration and Modic changes in the non-fused segments of patients with adolescent idiopathic scoliosis (AIS) who previously underwent spinal fusion. METHODS: Study subjects consisted of 252 patients with AIS who underwent spinal fusion between 1968 and 1988. Of 252 patients, 35 subjects underwent lumbar spine MRI and whole spine X-ray examination. The mean patient age at the time of follow-up was 49.8 years, with an average follow-up period of 35.1 years. We classified the subjects into two groups based on the lowest fused vertebra: H group whose lowest fused vertebra was L3 or higher levels and L group whose lowest fused vertebra was L4 or lower levels. RESULTS: The L group had significantly advanced disc degeneration on MRI. There was no significant difference between two groups in Modic changes. The L group showed less lumbar lordosis than the H group (H group: 48.1 degrees; and L group: 32.1 degrees) and greater SVA (H group: 1.2 cm; and L group: 5.5 cm). CONCLUSIONS: In AIS patients, 35 years after spinal fusion surgery on average, we evaluated lumbar disc degeneration and Modic changes of the non-fused segments. In patients with the lowest fusion level at L4 or lower, there were reduced lumbar lordosis, considerable SVA imbalance, and severe disc degeneration compared with those with the lowest fusion level at L3 or higher. The lowest fusion level at L3 or higher is recommended to reduce disc degeneration in midlife.