Validation of Intraoperative Pull-Up Strength Testing of an Interspinous Fixation Device for Immediate and Long-Term Clinical Stability: A Cadaveric and Prospective Clinical Study.

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.