Radiographic Evaluation after Anterior Spinal Fusion for Idiopathic Scoliosis

We studied 16 patients with lumbar or thoracolumbar idiopathic scoliosis treated with anterior spinal fusion alone. Four patients were men and 12 were women. The average age at the time of operation was 16.1 years, and the average follow-up time was 65 months. Preoperatively, the mean Cobb angle of the major curve was 60 degrees, which improved to 22.8 degrees after operation. The mean recovery rate of the Cobb angle was 63%. There were 7 patients in whom instrumentations ended one vertebra above the lowest end vertebra (Group A), whereas there were 9 patients in whom lowest end vertebras were involved in the instrumented areas (Group B). Postoperatively, the mean instrumented disc angle just below the lowest instrumented vertebra of the patients in group A was sigificantly greater than that of the patients in group B. Furthermore, in group A, frequency of posterior slip of the lowest instrumented vertebra was significantly greater than that in group B. These results suggest that there exists potential risk of disc degeneration just below the lowest instrumented vertebra when the lowest end vertebra is not involved in the fusion area.