Computed Tomography Hounsfield Units Better Predict Subsequent Fracture After Balloon-assisted Kyphoplasty Than Dual Energy X-Ray Absorptiometry T-scores

Introduction: Vertebral compression fractures (VCF) are a hallmark of osteoporosis and are the most prevalent fragility fracture. Hounsfield units (HFU) obtained by computed tomography (CT) and T-scores obtained by dual energy x-ray absorptiometry (DEXA) can assess bone density. This study examined the utility of HFUs and T-scores to predict subsequent adjacent-level fracture following balloon-assisted kyphoplasty (BAK).

Methods: A retrospective analysis of 126 patients who developed osteoporotic VCFs and underwent a single-level BAK at a single-institution was performed (2015-2022). Patients received both a CT and DEXA scan within 1 year of surgery. Traumatic and pathological fractures were excluded. Relevant clinical, demographic, and radiologic data were collected. Patients who developed a subsequent VCF were compared to those who did not. Multivariable regression was performed to identify factors independently associated with subsequent fracture.

Results: Of 126 patients, 26 patients (21%) developed a subsequent adjacent-level VCF after BAK. Patients who developed subsequent fractures were no different with respect to age (P=0.297), sex (P=0.217), chronic steroid use (P=1.000), and smoking status (P=0.130). Median T-scores were not significantly different between patients who had subsequent fractures (-2.4 [-3.1, -1.7]) and patients who did not (-2.45 [-3.1, -1.7]) (P=0.9975). The rate of subsequent fractures among patients with T-scores in the lowest quintile (-5.4 to -3.6) was 30%, compared to 25% among patients in the highest quintile (-1.6 to 2.7) (P=0.711). Adjacent-level HFU (OR=1.00 [0.99, 1.01], P=0.694) and T-score (OR=1.02 [0.71, 1.47], P=0.902) were not associated with subsequent fracture. However, the percent difference in HFU between supra- and subjacent levels was associated with subsequent fracture (OR=1.10 [1.04, 1.17], P=0.001).

Conclusion : Subsequent fracture risk after BAK could not be predicted by bone density assessed by either HFUs or T-scores. The percent difference in HFUs between supra- and subjacent vertebra to the level of BAK accurately predicted the development of subsequent adjacent-level fractures.