Opportunistic CT-Based Hounsfield Units Strongly Correlate with Biomechanical CT Measurements in the Thoracolumbar...

Retrospective cohort study.

Hounsfield units (HUs) are known to correlate with clinical outcomes, but no study has evaluated how they correlate with biomechanical computed tomography (BCT) and dual-energy x-ray absorptiometry (DXA) measurements.

Low bone mineral density (BMD) represents a major risk factor for fracture and poor outcomes following spine surgery. DXA can provide regional BMD measurements but has limitations. Opportunistic HUs provide targeted BMD estimates; however, they are not formally accepted for diagnosing osteoporosis in current guidelines. More recently, BCT analysis has emerged as a new modality endorsed by the International Society for Clinical Densitometry for assessing bone strength.

Consecutive cases from 2017 to 2022 at a single institution were reviewed for patients who underwent BCT in the thoracolumbar spine. BCT-measured vertebral strength, trabecular BMD, and the corresponding American College of Radiology Classification were recorded. DXA studies within three months of the BCT were reviewed. Pearson Correlation Coefficients were calculated, and receiver-operating characteristic curves were constructed to assess the predictive capacity of HUs. Threshold analysis was performed to identify optimal HU values for identifying osteoporosis and low BMD.

Correlation analysis of 114 cases revealed a strong relationship between HUs and BCT vertebral strength ( r =0.69; P <0.0001; R2 =0.47) and trabecular BMD ( r =0.76; P <0.0001; R2 =0.58). However, DXA poorly correlated with opportunistic HUs and BCT measurements. HUs accurately predicted osteoporosis and low BMD (Osteoporosis: C =0.95, 95% CI 0.89-1.00; Low BMD: C =0.87, 95% CI 0.79-0.96). Threshold analysis revealed that 106 and 122 HUs represent optimal thresholds for detecting osteoporosis and low BMD.

Opportunistic HUs strongly correlated with BCT-based measures, while neither correlated strongly with DXA-based BMD measures in the thoracolumbar spine. HUs are easy to perform at no additional cost and provide accurate BMD estimates at noninstrumented vertebral levels across all American College of Radiology-designated BMD categories.