Sagittal Alignment as a Risk Factor for Adjacent Level Degeneration: A Case-Control Study

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The purpose of this study is to determine whether sagittal alignment, preexisting degeneration at the adjacent level, and smoking predispose patients to the development of adjacent segment degeneration following lumbar fusion.

Fifty-one patients who underwent revision surgery for symptomatic adjacent segment degeneration from 1997 to 2003 were identified from a surgical database and matched with 51 control patients who did not develop adjacent segment degeneration based on age, sex, level, and date of index surgery. Sagittal alignment was measured through the fusion levels and from L1-S1, before and after index surgery. The amount of preexisting degeneration at the adjacent level was graded before index surgery and at latest follow-up using the UCLA grading system. Smoking rates were obtained from chart review.

The average age in both groups was 54 years. The average number of levels fused was 1.68. Patients with adjacent segment degeneration underwent revision surgery an average of 58 months following their index surgery. Cases who developed adjacent segment degeneration had significantly less lordosis through the fused levels (−15.4° for cases, −23.4° for controls) and the total lumbar spine (−46.3° for cases, −51.9° for controls) following their index surgery. No significant difference was noted in the amount of preexisting degeneration at the adjacent level and smoking rate between cases and controls.

Fusion of the lumbar spine in abnormal sagittal alignment, with loss of lumbar lordosis, predisposes the patient to the development of adjacent segment degeneration. Adjacent segment degeneration does not appear to be just a progression of preexisting degenerative changes at the adjacent level.

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