# Dynamic Interspinous Process Distance and Adjacent Vertebral Fracture After Balloon Kyphoplasty: Preliminary Evidence From a Single-Center Cohort

## TL;DR

This study suggests that changes in interspinous process distance after a spinal procedure may predict future fractures in nearby vertebrae.

## Contribution

The study introduces dynamic interspinous process distance as a potential predictor of adjacent vertebral fractures after balloon kyphoplasty.

## Key findings

- Normalized ΔISPD was significantly associated with adjacent vertebral fractures (p < 0.05).
- Thresholds of ≥3.4 mm and ≥5.5 mm in ISPD change showed moderate predictive performance (AUC 0.750 and 0.759).
- Dynamic ISPD changes appear to be a reproducible and easily obtainable radiographic marker for fracture risk.

## Abstract

Purpose: The aim of this study was to investigate whether dynamic changes in interspinous process distance (ΔISPD) between standing and supine positions predict adjacent vertebral fractures (AVFs) following balloon kyphoplasty (BKP) for thoracolumbar osteoporotic vertebral fractures (OVFs). We hypothesized that greater ΔISPD reflects posterior instability and is associated with a higher risk of AVF.

Overview of literature: AVF is a common complication after BKP. Risk factors such as low bone mineral density and endplate injury have been identified, but little attention has been paid to dynamic posterior instability as evaluated by ΔISPD.

Methods: This retrospective observational exploratory pilot study included 36 patients (mean age, 81.8 years) who underwent BKP for thoracolumbar OVFs between 2019 and 2023. ISPD was measured at levels adjacent to the fractured vertebra in both standing and supine lateral radiographs. ΔISPD was normalized to anterior vertebral body height and multiplied by 100 for analysis. Interobserver and intraobserver reliability was assessed. Univariate analyses were conducted using the Mann-Whitney U test or Fisher’s exact test, as appropriate. Receiver operating characteristic (ROC) curve analyses were performed to determine optimal cutoff values for ΔISPD and normalized ΔISPD associated with AVF occurrence.

Results: AVFs occurred in 12 patients (33%). Normalized ΔISPD was significantly associated with AVF occurrence (p < 0.05). These thresholds corresponded to physical ISPD changes of ≥3.4 mm and ≥5.5 mm, respectively. ROC analysis demonstrated moderate predictive performance with area under the curve (AUC) values of 0.750 (upper, 95% CI, 0.58-0.93) and 0.759 (lower, 95% CI, 0.57-0.95).

Conclusions: Dynamic ISPD changes were significantly associated with AVF after BKP. Although this study was limited by the small sample size and event count, normalized ΔISPD appears to be a reproducible and easily obtainable radiographic marker that may aid in identifying patients at high risk for AVF. Incorporating ΔISPD into preoperative assessment could improve risk stratification, but prospective multicenter validation is warranted.