Distal Ulnar Hounsfield Units Accurately Predict Bone Mineral Density and Future Fragility Fracture Risk: Level 3 Evidence

Abstract

There is no financial information to disclose. Hounsfield unit (HU) measurement from wrist computed tomography (CT) may provide an effective screening tool for low bone mineral density (BMD). We hypothesized that HU measurements from wrist CT scans would accurately evaluate forearm BMD, and low HU values would effectively predict the occurrence of fragility fractures. An electronic database of radiographs was queried for all wrist CT scans obtained at a single institution, and a database of all active duty and military dependents was cross-referenced with the CT scan population to identify all patients with both wrist CT and DXA. Hounsfield unit measurements were performed by one author blinded to DXA results on sequential coronal CT slices of the distal ulnar head. Average HU values were compared to forearm and femoral neck T-score determined by DXA scan. Medical records were then manually reviewed for the occurrence of any fragility fracture. There were 161 CTs in 159 patients included; 74 patients also had available DXA scans. For the population with both CT and DXA, average HU were significantly lower in the DXA-confirmed osteoporotic and osteopenic groups when compared to the normal BMD group (98.1 and 126.9HU versus 198.6HU, respectively, P < 0.0001). The upper limit 95% confidence interval for forearm osteopenia patients was 145.8HU. Overall, the prevalence of fragility fractures was 15.7%. Average HU in the fragility fracture group was significantly lower (126.2 versus 200.5HU, P < 0.0001). The percentage of patients with HU below 145.8HU who subsequently sustained fragility fractures was significantly higher (29.5% versus 2.5%, P < 0.0001). The odds ratio for fragility fracture in the low HU group was 16.9 (range: 3.8 to 74.6). The sensitivity of forearm HU for fragility fracture risk was 92.3%, with a negative predictive value of 97.5%. •Patients with low BMD of the forearm and femoral neck had significantly lower HU measurements in the distal ulna on CT when compared to patients with normal BMD, and measurements below 145.8HU were strongly associated with low BMD.•Patients with HU below 145.8HU were 16 times more likely to sustain a subsequent fragility fracture. Using this cutoff, we were able to predict 92% of fragility fractures.•Distal ulnar HU measurements can be performed easily to identify patients with osteoporosis, and to accurately recognize patients at significant risk for fragility fractures.