What question did this study set out to answer?

To validate the intraoperative pull-up strength of the InSpan interspinous fixation device for stability assessment.

April 4, 2026Clinical Spine Surgery A Spine Publication0 citations

Validation of Intraoperative Pull-Up Strength Testing of an Interspinous Fixation Device for Immediate and Long-Term Clinical Stability

KCKingsley R. ChinFlorida International University MJMark R. JonesCharles River Laboratories (Netherlands)STSandra ThompsonBoise State University

Key Points

To validate the intraoperative pull-up strength of the InSpan interspinous fixation device for stability assessment.
Conducted a prospective multicenter study on cadaveric models and patients undergoing L4–5 decompression.
Included 29 cadaver cases and 21 patient cases, treated over 6 months.
Evaluated implant stability using thumb-index finger and body lift-off pull tests, with physical and fluoroscopic confirmation.
Followed patients for up to 24 months, recording Visual Analog Scale and Oswestry Disability Index scores.
All 29 cadavers passed pull-up tests with no implant loosening.
95% of patient surgeries achieved successful pull-up test results on the first attempt.
Two-year follow-up showed significant improvements in VAS (79.44%) and ODI (68.56%) scores (P < 0.001).
Radiographic assessments confirmed stable implants with no loosening or fractures.

Abstract

Study Design: Prospective, multicenter study on cadaveric models and patients undergoing L4–5 decompression and interspinous fixation device (IFD) placement. Objective: To validate the intraoperative pull-up strength of the InSpan (InSpan LLC, Burlington, MA) IFD as a standalone device, assessing its immediate and long-term stability. Summary of Background Data: Interspinous fixation devices (IFDs) are used in spinal stenosis treatment and fusion procedures to distract the disc and foraminal space, providing posterior stabilization. Despite their utility, concerns about spinous process fractures and implant loosening persist. Methods: A total of 50 cases, including 29 cadavers (group 1) and 21 patients (group 2), underwent L4–5 decompression with InSpan IFD placement. Over 6 months, 21 patients were consecutively enrolled at 3 sites, treated by interventional pain management and spine surgeons, with 100% recruitment. Implant stability was tested intraoperatively using a thumb-index finger pull test, followed by a body lift-off pull-up test, with confirmation through physical and fluoroscopic evaluation. Patients were followed for up to 24 months, and outcome measures such as the Visual Analog Scale (VAS) and Oswestry Disability Index (ODI) scores, implant failure, and revision rates were recorded. Results: All 29 cadavers in group 1 passed the pull-up tests without implant loosening. In group 2, 95% (20/21) of primary IFD surgeries passed on the first attempt, whereas 1 revision case failed the body lift-up test and required further decompression. Two-year follow-up for 14 patients showed significant improvements in VAS (79.44%) and ODI (68.56%) scores ( P <0.001). Radiographic assessments confirmed stable implants with no loosening or fractures. Males had longer surgery times ( P <0.05), but outcomes were similar across genders. Conclusions: The InSpan IFD provides significant immediate and long-term stability. The pull-up test is a reliable method to assess intraoperative fixation, with potential applications in suspected inadequate fixation cases. Level of Evidence: Level III.

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