ABSTRACT
The long-term success of arthrodesis for degenerative conditions in the lumbar spine depends on many factors, including the effects of arthrodesis on the transition zone between the last fused level and the next untreated level. As rigid internal fixation with spinal instrumentation has been performed, there has been interest in the effects the arthrodesis has on accelerating transition zone degeneration (1-3). These changes are summarized as adjacent segment disease (ASD), and include: listhesis, scoliosis, instability, herniated disc, osteophyte formation, arthritis, stenosis, and vertebral compression fracture (4). Hardware, the approach used, and the level of instrumentation have been the reported causes of accelerated degeneration above and below instrumented fusions (4). Other reports have indicated that the degenerative changes may not be greater than those expected with the natural history of the degenerative process, as degenerative disease is not expected to be isolated to one level (4-7). Reports that have suggested an increased risk of adjacent segment degeneration indicate that there are several risk factors for this condition, including age, gender, bone quality, levels of instrumentation, associated degenerative changes at the time of index surgery, history of previous surgeries, and so on (8-12). Owing to the lack of understanding of ASD etiology, incidence rates have been reported between 8% and 100%, using radiographic criteria and between 5.2% and 18.5%, using symptomatic criteria (4). However, few have looked specifically at multilevel arthrodesis as a risk factor for accelerated transition zone degeneration at the cephalad end vertebra and the effects on both radiographic and clinical criteria.
