Sagittal Section Hounsfield Units of the Upper Instrumented Vertebrae as a Predictor of Proximal Junctional Vertebral Fractures Following Adult Spinal Deformity Surgery

Study Design: A retrospective observational study. Purpose: This study aimed to determine an accurate and convenient screening method for predicting proximal junctional fractures (PJFr) following surgery for adult spinal deformity (ASD) using computed tomography (CT)-based measurement of Hounsfield units (HUs). Overview of Literature: CT-based measurement of HUs is an alternative tool for assessing bone mineral density. However, the opti-mal method for predicting adjacent vertebral fractures following spinal fusion using HUs remains unclear. Methods: This retrospective observational study included 42 patients who underwent reconstructive surgery for ASD. Elliptical re-gions of interest (ROIs) on the axial section and rectangular ROIs on the sagittal section were placed at the upper instrumented verte-brae (UIV), UIV+1, and UIV+2. In addition, the HU value of the L2 vertebra was used as the representative. Results: PJFr occurred in 28.6% of patients within 2 years following surgery. The HU values obtained from the axial sections of L2, UIV, UIV+1, and UIV+2 were not significantly associated with the incidence of PJFr within 2 years, except for the ROI set in the lower region of the L2 vertebra. However, the HU value of the anterior third of the UIV in the sagittal section was significantly lower in the PJFr group than in the nonPJFr group (87.0 vs. 160.3, p=0.001). A UIV HU value of <100 was associated with a higher incidence of PJFr than an HU vaue of >100 (p<0.05). Conclusions: Measurements of HU in the anterior one-third of the UIV in the sagittal section demonstrated predictive ability for PJFr following ASD surgery. A UIV HU value of <100 emerged as a risk factor for PJFr