The vertebral Hounsfield units can quantitatively predict the risk of adjacent vertebral fractures after percutaneous kyphoplasty

BACKGROUND: Measuring the Hounsfield units (HU) of the vertebrae may yield diagnostic information for fracture risk. This study aimed to measure HU of vertebrae in percutaneous kyphoplasty (PKP) patients using computed tomography (CT) imaging to determine the HU measurements threshold for adjacent vertebral fracture and to assess the relationship between HU measurements and the risk of adjacent vertebral fracture. METHODS: A retrospective study was conducted on consecutive patients who underwent PKP between January 2019 and October 2021 in the China-Japan Union Hospital of Jilin University. The HU of the vertebra was measured on the reconstructed CT images by 2 independent spine surgeons. The HU measurements of adjacent vertebrae and the ratio of HU measurements between the surgical vertebra and adjacent vertebrae were statistically analyzed to determine the best critical value and evaluate the prediction effectiveness and accuracy of the best critical value. RESULTS: A total of 105 patients were identified with complete imaging and follow-up information. Of these, 47 patients (44.8%) had evidence of an adjacent vertebral fracture on follow-up imaging. The mean HU measurements of the fractured adjacent vertebra were significantly different from the mean HU measurements of the unfractured adjacent vertebra (50.94±20.59 vs. 81.74±18.97 HU; P<0.001). There was a significant difference in the ratio of HU measurements between the surgical vertebra and the fractured adjacent vertebra and between the surgical vertebra and the unfractured adjacent vertebra (26.34±17.52 vs. 14.53±9.40; P<0.001). Interactive scatter plots and receiver operating characteristic (ROC) curve showed that a HU measurement of 66.9 and a HU measurements ratio of 15.18 were the best thresholds for predicting the risk of fracture of adjacent vertebrae after PKP surgery, with an area under the curve (AUC) of 0.901 [95% confidence interval (CI): 0.822–0.953; P<0.001] and 0.874 (95% CI: 0.790–0.934; P<0.001), respectively. The prediction accuracy was 90.4% and 84.0%, respectively. CONCLUSIONS: A low mean HU measurements of adjacent vertebrae or a high ratio of the mean HU measurements of the operated vertebrae to the adjacent vertebrae are risk factors for the vulnerability of adjacent vertebrae to fracture. The risk of fracture in the adjacent vertebrae after PKP can be predicted by measuring HU.