Spine surgeons have long believed that fusion likely accelerates degeneration at adjacent levels, though the data supporting this belief has been limited. In general, long-term RCTs comparing fusion to non-operative treatment have been underpowered to evaluate adjacent segment disease (ASD) in the long-term, so the question has remained unanswered. In order to overcome the reduced power related to attrition, Dr. Mannion and her colleagues combined data from four major RCTs comparing fusion to non-operative treatment for low back pain and obtained radiographs and patient-reported outcome measures at a mean follow-up of over 13 years. While just over 50% of patients were lost to follow-up, over 350 patients were included in the analysis, making this the largest data-set ever collected to look at long-term ASD after lumbar fusion. They found that the fusion group had significantly greater loss of disk height at the adjacent level and two segments cranial to the fused level. However, there was no correlation between disk height loss and clinical outcome measures (ODI and low back pain scale). This led the authors to conclude that while fusion had at least some role in accelerating ASD, this was not symptomatic, at least out to 13 years.
The authors should be congratulated on working together to create such a large dataset with long-term follow-up in an attempt to answer the age-old question about fusion and ASD. The paper does provide rather compelling evidence that fusion does accelerate ASD, but that development of ASD has minimal effect on clinical outcomes. The most concerning aspect of this study is the large loss to follow-op, though nearly 50% follow-up over a decade from enrollment is actually quite good. There were also a substantial number of crossovers from non-operative treatment to surgery. While these factors could cause selection and attrition bias, there was no indication that the patients who were lost to follow-up or crossed over were much different than those who did not. One could also suggest that disk height loss may not be the best marker for ASD and that MRI findings and/or dynamic radiographs would be better. Despite these minor shortcomings, this paper represents the best data on this topic in the lumbar spine.
Please read Dr. Mannion’s article in the August 1 issue. Does this paper change how you think about ASD after lumbar fusion? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor