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Lønne, Greger MD

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doi: 10.1097/BRS.0000000000000823
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In our study “Minimally Invasive Decompression Versus X-Stop in Lumbar Spinal Stenosis: A Randomized Controlled Multicenter Study,”1 the enrolment was stopped after a midway interim analysis because of a high reoperation rate in the interspinous spacer group. Lurie claims in his “Point of view”2 that the stopping of the enrollment was unfortunate. He correctly stated that “there do not seem to have been a priori stopping rules” for the interim analysis.

A midway interim analysis was planned to reduce study participants' exposure to the inferior treatment, either by revealing an early significant difference in outcome or by an obvious negative side effects in one of the groups. High reoperation rate in the X-stop group was a significant clinical finding, a clear disadvantage to the patients and could, therefore, not be ignored. Continuing the enrollment with this, at the time, new knowledge would introduce a bias to the study. The study group also considered it as unethical, given the risk for an additional operation of around 30%. In the early studies of X-Stop, the rate of secondary surgery after 2 years was low (6%).3 The high risk for a reoperation was unknown to us when planning this study. Some later studies show similar high reoperation as in our study.4

At 2 years of follow-up, the intention-to-treat-analysis showed no significant difference in the primary and secondary outcomes. Lurie claims: “As a result, this study does not particularly add to our knowledge of the proper role for interspinous spacers in lumbar spinal stenosis.” This study was designed to compare X-Stop with minimally invasive decompression and must be interpreted in that context. Despite its weakness, a significantly higher reoperation rate within 2 years in the X-Stop group is a clear finding and valuable knowledge to many patients and surgeons in the decisionmaking process.


1. Lønne G, Johnsen LG, Rossvoll I, et al. Minimally invasive decompression versus x-stop in lumbar spinal stenosis: a randomised controlled multicenter study. Spine (Phila Pa 1976) 2015;40:77—85.
2. Lurie JD. Point of view. Spine 2015;40:77—85.
3. Zucherman JF, Hsu KY, Hartjen CA, et al. A multicenter, prospective, randomized trial evaluating the X STOP interspinous process decompression system for the treatment of neurogenic intermittent claudication: two-year follow-up results. Spine (Phila Pa 1976) 2005;30:1351—1358.
4. Stromqvist BH, Berg S, Gerdhem P, et al. X-stop versus decompressive surgery for lumbar neurogenic intermittent claudication: randomized controlled trial with 2-year follow-up. Spine (Phila Pa 1976) 2013;38:1436—1442.
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