Long-term results demonstrate that even though implantation of a stand-alone interspinous process device (IPD) can be successful in treating intermittent neurogenic claudication (INC), the high reoperation rate does not justify its use and simple decompression is more effective. This is the finding of a five-year double blind RCT, results of which were presented at the 2019 Eurospine annual meeting (16-18 October, Helsinki, Finland).
Short-term results comparing IPD to conventional decompression in patients with INC due to lumbar spinal stenosis provide evidence that clinical outcomes are comparable, but that reoperation rates are higher in the IPD group, Catharina Schenck (University Medical Centre, Leiden, The Netherlands), the study’s lead author told the Eurospine meeting. Schenck and colleagues focused on long-term, five-year results of this comparison.
Patients with neurogenic claudication due to lumbar spinal stenosis at one or two levels who had failed to respond to conservative treatment between 2008-2011, were randomised to receive either standard bony decompression or standalone implantation of an IPD (Coflex). A total of 159 patients were randomised at the five participating neurosurgical centres. 80 participants received an IPD without bony decompression and 79 participants underwent only spinal bony decompression. Patients and research nurses remained blinded for the allocated treatment up to one year after surgery.
The primary outcome at five years was the score for the Zurich Claudication Questionnaire (ZCQ), and secondary outcome measures included Visual Analogue Scores (VAS) for back pain and leg pain. Repeated-measurement analyses were applied to compare outcomes over time.
Schenck said that the recovery rates based on the ZCQ were similar for the two groups, with 68% in the IPD group having experienced successful recovery, compared to 56% in the standard decompression group (p-value 0.422). Reoperations, because of absence of recovery, remained significantly higher in the IPD group compared to standard decompression with comparable reoperation rates at two and five years (p=0.04), Schenck and colleagues found. Long-term back pain was lower in the IPD group [26 mm on a 100 mm scale (95% CI 20-32)] compared to the bony decompression group [38 mm (95% CI 30-46) p-value 0.02]. This is in contrast to the two-year results where the VAS back pain was higher in the IPD group compared to standard bony decompression (36 vs. 28 mm, p-value 0.04).
Schenck concluded: “I think we can conclude that the reoperation rates in the IPD group are higher at two years, and in ongoing analysis we see comparable results at five years, and self-reported back pain seems lower for the IPD group at five years. The reoperation rate in the IPD group is high and the cost for the IPD adds to the disadvantages, but in spite of this I think we can say that once the IPD works it works.” Standard decompression remains the golden standard, Schenck said, since it is effective and lacks the disadvantages of the IPD.
The study’s authors note that the difference in VAS back pain between both treatment groups at five years might be statistically significant, but is clinically probably non-relevant. Implanting an IPD is not unacceptable, but it is a costlier alternative for decompressive surgery carrying a higher reoperation risk, they note.