There have been relatively few long-term comparative studies evaluating surgical and non-operative outcomes for lumbar spinal stenosis (SpS). Dr. Lurie and his colleagues published the 8 year data from the Spine Patient Outcomes Research Trial (SPORT) SpS cohort in the January 15 issue. Most readers are familiar with the design of the trial, which included a simultaneous RCT and observational study comparing surgical and non-operative outcomes for SpS patients. Analysis of the RCT with the traditional intent to treat (ITT) methodology was hampered by the high rate of crossover: only 70% of patients assigned to surgery actually had surgery within 8 years, while 52% of patients assigned to non-operative treatment did have surgery. As such, the primary analysis was an as-treated (AT) analysis, which was performed separately for the RCT and observational groups. In the randomized group, surgery patients had significantly better patient-reported outcomes through 4 years, though the benefit of surgery was no longer significant after 5 years. In contrast, the surgery patients in the observational cohort were still doing significantly better than their non-operative counterparts even at 8 years. Both analyses controlled for baseline differences. Overall, there was an 18% re-operation rate, with 10% of surgical patients undergoing an additional operation for recurrent stenosis or progressive spondylolisthesis. There was a high loss to follow-up, with only 55% of the RCT and 52% of the observational cohort patients included in the 8 year analysis.
This report reflects the difficulty of long-term studies comparing surgery to non-operative treatment. Not surprisingly, loss to follow-up was nearly 50%, and those who were lost were significantly different than those who did follow-up; they were older, sicker, less educated, and had worse outcomes at 2 years. The authors suggested that this likely led to an overestimate of the absolute degree of improvement at 8 years, but that the treatment effect estimate was likely accurate given that those lost to follow-up did worse with both surgical and non-operative treatment. Of the randomized patients assigned to non-operative treatment, 52% had surgery within 8 years, indicating that patients are unlikely to remain compliant with randomization if non-operative treatment fails. Even among the observational cohort patients who initially chose non-operative treatment, 25% had gone onto surgery within 3 years. The combination of loss to follow-up and crossover, which was inevitable in this study design, makes interpreting the outcomes difficult, especially since the results were substantially different in the RCT AT analysis and the observational cohort. The authors suggested that the RCT AT analysis might be less affected by selection bias than the observational cohort as baseline differences between the surgical and non-operative groups were less pronounced—though still significant—in the RCT AT analysis. This view led them to conclude that the benefit of surgery likely decreases beyond 5 years. Similar results were reported in the Maine Lumbar Spine Study that showed diminution of the advantage of surgery from 5-10 years, though some significant differences did persist in the long-term.1 On the whole, the literature does suggest that surgery results in better outcomes out to 5 years but that the benefits of surgery likely erode over time as patients age and develop recurrent stenosis, spondylolisthesis, and adjacent segment degeneration. In a perfect world, an RCT would be performed with no crossover and 100% follow-up for twenty years. In reality, SPORT has likely done as good as is possible in a study of human subjects, and the authors and the participating patients should be congratulated on their efforts to produce long-term data.
Please read Dr. Lurie’s article in the January 15 issue. Does this change your views of long-term outcomes in spinal stenosis? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor
1. Atlas SJ, Keller RB, Wu YA, Deyo RA, Singer DE. Long-term outcomes of surgical and nonsurgical management of lumbar spinal stenosis: 8 to 10 year results from the maine lumbar spine study. Spine 2005;30:936-43.