RESUMEN
STUDY DESIGN: A retrospective study. OBJECTIVE: To evaluate the usefulness of MRI grading of disc degeneration in determining whether L5-S1 fusion is necessary in degenerative lumbar spinal disorders. SUMMARY OF LITERATURE REVIEW: Changes in adjacent segments are not well understood, after floating fusion has been performed. MATERIALS AND METHODS: We reviewed 16 surgical cases of degenerative lumbar spinal disorders from July 1996 to February 2000 with an average follow-up of 41 months. Fusion was done in patients without instability, pathology and narrowing of L5-S1. We measured the disc degeneration of adjacent segments in preoperative MRIs using the Modified Pearce classification. In spine AP, lateral and flexion-extension radiographs, we measured disc height, angular motion and instability changes and correlated these with disc degeneration. RESULTS: Disc height changes decreased in the upper and lower adjacent segments and preoperative disc degeneration above grade IV, decreased more in lower adjacent segment. A statistical correlation was found between disc degeneration and disc height changes in the lower segment (P=0.046), but not in the upper segment (P=0.649). The angular-motion was unchanged in the upper and lower adjacent segments, and no statistical correlation was found between disc degeneration and angular-motion changes (P=0.819, 0.208). Postoperative instability was found in the upper adjacent segment in 2 patients, but no statistical cor-relation was found between disc degeneration and instability (P=0.083, P=1.000). CONCLUSION: L5-S1 might be saved when free of pathology, and when disc degeneration is below grade III and balanced sagit-tally. However, further study is needed because of the short-term follow up and low number of cases in this study.