Poster Presentation 51st International Society for the Study of the Lumbar Spine Annual Meeting 2025

Purpose: When balloon kyphoplasty (BKP) is performed for osteoporotic vertebral fractures (OVF), intervertebral bridging ossification (IBO) occasionally forms between the fractured and adjacent vertebrae, contributing to regional stabilization. Despite previous reports, the factors associated with IBO remain unclear due to insufficient cases. This study aimed to clarify preoperative factors associated with intervertebral bridging ossification.

Methods: Consecutive patients who underwent BKP for OVF between May 2011 and December 2017 were analyzed. The inclusion criteria were as follows: (1) age ≥ 65 years, (2) acute OVF within 1 month of onset of symptoms, (3) underwent magnetic resonance imaging (MRI) at enrollment, and (4) at least 1 year of follow-up. Preoperative radiological evaluation included the location of the fractured vertebra, number of preexisting vertebral fractures, endplate damage to the fractured vertebra, lateral wedge angle of the fractured vertebra (Fig.1, α1), and regional kyphosis angle (Fig.1, α2), including the upper and lower vertebrae, using radiography, computed tomography, and MRI. Intervertebral disc changes were evaluated using the midsagittal T2-weighted signal ratio on MRI. Signal intensity (SI) values were acquired using the region of interest as the center of the disc and the conus medullaris of the spinal cord. We recorded disc SI at the proximal and distal intervertebral discs adjacent to the fractured vertebrae (Fig.2). The signal ratios were calculated using the following formulas: Signal ratio = SIdisc/SIcord. IBO was defined as complete bridging of the intervertebral space by ossification, confirmed either on the sagittal or coronal views of the CT images.

Results: A total of 134 patients who underwent BKP completed the 1-year follow-up period. In this study, the overall rate of IBO was 26.9%. Patients were divided into groups with and without IBO, and the two groups were compared. Compared to patients without IBO, patients with IBO had a greater proportion of vertebral fractures located at the thoracolumbar junction (T11–L2) (p<0.001), a greater number of preexisting vertebral fractures (p<0.001), a greater proportion of proximal endplate injury of the fractured vertebra, a higher MRI T2-weighted signal ratio of the intervertebral disc adjacent to the proximal side of the fractured vertebra (p=0.015), and a greater lateral wedge angle of the fractured vertebra in the supine (p=0.008) and sitting positions (p=0.001). In addition, multiple regression analysis showed that only the number of pre-existing vertebral fractures (p<0.001) and proximal endplate injuries (p=0.002) were significantly associated with IBO formation.

Discussion: In this study, we found that preexisting vertebral fractures and proximal endplate injury of the fractured vertebra were predictors of IBO formation after BKP. Preexisting vertebral fractures are associated with sagittal malalignment and lead to an increased axial load on new vertebral fractures. A mechanical axial load stimulates callus formation and new bone deposition during bone-fracture healing. In endplate injury, blood leakage from the vertebral body can form a hematoma, and an inflammatory reaction is initiated at the injury site. Inflammation causes the secretion of various growth factors and cytokines. The process will promote the formation of IBO, which is similar to the fracture healing mechanism.