A comparison of MRI and intraoperative measurements to determine interspinous spacer device size.

Purpose: To determine whether preoperative magnetic resonance imaging (MRI) can reliably determine intraoperative measurements in the Vertiflex Interspinous Spacer (ISS) procedure.

Methods: Patients who underwent Vertiflex ISS with Lumbar Spinal Stenosis (LSS) and a preoperative MRI available in picture archiving and communication system (PACS) between January 2013 to February 2023 were identified retrospectively from the University of Chicago Medical Center Database. An experienced board-certified pain specialist and well-trained 2nd-year medical student independently performed measurements of the interspinous space where Vertiflex ISSs of various sizes are inserted. MRI measurements were taken blinded to intraoperative measurement and ISS implant size used in the procedure. Pearson's correlation, paired T-test, intraclass correlation coefficients (ICC), absolute agreement, and 2-way random effects model were used to determine the relationships between MRI, intraoperative measurement, and ISS size.

Results: A total of 79 patients who underwent the Vertiflex ISS procedure were included in the study. Median Vertiflex ISS size was 10 mm (10-12), mean intraoperative measurement was 11.40 mm (±1.23), and mean MRI measurement was 11.24 mm (±1.44). Mean differences were not significant in intraoperative and MRI measurements (p = 0.271). Pearson's correlation between ISS size and intraoperative measurement was 0.807 (p < 0.001), representing the current best practice model. Pearson's correlation was 0.668 (p < 0.001) between MRI measurement and ISS size and 0.542 (p < 0.001) between MRI and intraoperative measurement. ICC showed good agreement and moderate reliability (0.698) between intraoperative and MRI measurements. Observer interrater ICC agreement of the MRI interspinous space measurement was 0.95 (p < 0.001).

Conclusions: Measuring interspinous space on MRI yielded, on average, a value smaller than the intraoperative measurement in Vertiflex ISS procedures, but the mean differences were not significant. Good agreement and moderate reliability were found between observer MRI and surgeon intraoperative measurements, suggesting MRI can evaluate the intraoperative space for the Vertiflex ISS procedure. Preoperative MRI measurement may help decrease complications by aiding in surgical decision-making through providing a reference for intraoperative measurements. Further prospective study is necessary to determine if preoperative MRI measurement can predict and potentially replace the need for intraoperative measurement.