Abstract
INTRODUCTION: Numerous in-vitro studies demonstrating increased stress at levels adjacent to a lumbar fusion have raised concerns of accelerated degeneration. However, the significance of this increased stress in the in-vivo setting remains unclear, especially with long-term follow-up. The objective of this study is to assess the level of degeneration on MRI in this same cohort of patients at a minimum of twenty years follow-up.
METHODS: Twenty-five patients undergoing one or two level anterior lumbar interbody fusion at the L5-S1 or L4-5 levels with a minimum of twenty-years follow-up were identified. Only patients with normal pre-operative discograms at the level adjacent to the fusion were considered in this study. MRI scans were performed and evaluated for any evidence of degeneration by an independent radiologist. Advanced degeneration was defined as either: (1) absence of T2 signal intensity in the disk, (2) disk herniation, or (3) spinal canal stenosis. RESULTS: Advanced degeneration was identified in five (20%) patients, with three (12%) being isolated to the adjacent level. Fourteen (56%) other patients had evidence of early degeneration in their lumbar spine. Overall, eight (32%) patients had some evidence of degeneration isolated to the level adjacent to the disk whereas seven (28%) patients had multilevel degeneration and four patients (16%) had degeneration in their lumbar spine but preservation of the adjacent level.
DISCUSSION AND CONCLUSION: Without a control group, it is difficult to make firm conclusions on whether the changes seen on MRI represent the natural history of spinal deterioration or represent accelerated degeneration. However, after twenty years, only a handful of patients developed advanced adjacent level degeneration. Furthermore, the majority of degenerative changes seen occurred over multiple levels or at levels not adjacent to the fusion, suggesting that changes seen may be more likely related to constitutional factors inherent within the individual as opposed to the increased biomechanical stresses at the adjacent levels.
These abstracts were prepared by Dr Robert J. Moore. Correspondence should be addressed to him at Spine Society of Australia, Institute of Medical and Veterinary Science, The Adelaide Centre for Spinal Research, Frome Road, Adelaide, South Australia 5000.
