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Interspinous process device versus standard conventional surgical decompression for lumbar spinal stenosis: randomized controlled trial

BMJ 2013; 347 doi: (Published 14 November 2013) Cite this as: BMJ 2013;347:f6415
  1. Wouter A Moojen, neurosurgery resident and epidemiologist12,
  2. Mark P Arts, neurosurgeon2,
  3. Wilco C H Jacobs, epidemiologist1,
  4. Erik W van Zwet, statistician3,
  5. M Elske van den Akker-van Marle, health economist4,
  6. Bart W Koes, epidemiologist5,
  7. Carmen L A M Vleggeert-Lankamp, neurosurgeon1,
  8. Wilco C Peul, neurosurgeon and epidemiologist12
  9. for the Leiden-The Hague Spine Intervention Prognostic Study Group (SIPS)
  1. 1Department of Neurosurgery, Leiden University Medical Center, Leiden, Netherlands
  2. 2Department of Neurosurgery, Medical Center Haaglanden, The Hague, Netherlands
  3. 3Department of Medical Statistics and Bioinformatics, Leiden University Medical Center
  4. 4Department of Medical Decision Making, Leiden University Medical Center
  5. 5Department of General Practice, Erasmus Medical Center, Rotterdam, Netherlands
  1. Correspondence to: W A Moojen w.a.moojen{at}
  • Accepted 7 October 2013


Objective To assess whether interspinous process device implantation is more effective in the short term than conventional surgical decompression for patients with intermittent neurogenic claudication due to lumbar spinal stenosis.

Design Randomized controlled trial.

Setting Five neurosurgical centers (including one academic and four secondary level care centers) in the Netherlands.

Participants 203 participants were referred to the Leiden-The Hague Spine Prognostic Study Group between October 2008 and September 2011; 159 participants with intermittent neurogenic claudication due to lumbar spinal stenosis at one or two levels with an indication for surgery were randomized.

Interventions 80 participants received an interspinous process device and 79 participants underwent spinal bony decompression.

Main outcome measures The primary outcome at short term (eight weeks) and long term (one year) follow-up was the Zurich Claudication Questionnaire score. Repeated measurements were made to compare outcomes over time.

Results At eight weeks, the success rate according to the Zurich Claudication Questionnaire for the interspinous process device group (63%, 95% confidence interval 51% to 73%) was not superior to that for standard bony decompression (72%, 60% to 81%). No differences in disability (Zurich Claudication Questionnaire; P=0.44) or other outcomes were observed between groups during the first year. The repeat surgery rate in the interspinous implant group was substantially higher (n=21; 29%) than that in the conventional group (n=6; 8%) in the early post-surgical period (P<0.001).

Conclusions This double blinded study could not confirm the hypothesized short term advantage of interspinous process device over conventional “simple” decompression and even showed a fairly high reoperation rate after interspinous process device implantation.

Trial registration Dutch Trial Register NTR1307.


  • We thank the research nurses, the physicians who included patients, and the data manager of the SIPS group for their work in making this trial possible.

  • Nurses and data collection and management: M Nuyten, P Bergman, S Dukker, L Smakman (management), C Waanders, J Blom, J Videler, M de Raaf, M de Gooijer, J Vogelaar.

  • Participating hospitals and coordinating physicians: Medical Center Haaglanden, The Hague—M P Arts; Diaconessen Hospital, Leiden—R W Koot; Groene Hart Hospital, Gouda—J A L Wurzer; Spaarne Hospital, Hoofddorp—C L A M Vleggeert-Lankamp; Haga Hospital, The Hague—C F E Hoffmann; Rijnland Hospital, Leiderdorp—J H C Voormolen and M J T Verstegen; University Medical Center Utrecht—G J Amelink; Isala Klinieken Zwolle—F C de Beer; Vlietland Schiedam—R Walchenbach; Alkmaar Medical Center—W F Tan; Leiden University Medical Center, Leiden—W C Peul and J H C Voormolen;

  • Contributors: WAM, BWK, MPA, and WC P formed the Protocol Committee and were responsible for conception and design of the study. BWK, WAM, and WCP formed the Steering Committee. WAM, WCHJ, and EWvZ did the statistical analysis. WAM, WCP, CLAMV-L, MPA, and MEvdA-vM were involved in drafting and revising the manuscript. All authors approved the final version of the manuscript. WAM and WCP are the guarantors.

  • Funding: Paradigm Spine funded this trial. Paradigm Spine had no role in data collection, design of the study, data analysis, interpretation of data, or writing the report and had no influence over whether to submit the manuscript. All the researchers were individually independent from funders.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at and declare that the FELIX trial was funded by Paradigm Spine/InSpine and was carried out by the Leiden-The Hague SIPS group; no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: The medical ethics committees at the 11 participating hospitals approved the protocol, including an approval for randomization after anesthetic induction. More information can be obtained from the central ethics committee at Leiden (decision letter P08.009). Written informed consent was obtained from all patients.

  • Data sharing: Technical appendix, statistical code, and dataset are available from the corresponding author at w.a.moojen{at} Participants gave informed consent for data sharing.

  • Transparency declaration: The leading author (W C Peul) affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant registered) have been explained.

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