Estimating the density of femoral head trabecular bone from hip fracture patients using computed tomography scan data

Abstract

The purpose of this study was to compare computed tomography density ( ρCT) obtained using typical clinical computed tomography scan parameters to ash density ( ρash), for the prediction of densities of femoral head trabecular bone from hip fracture patients. An experimental study was conducted to investigate the relationships between ρash and ρCT and between each of these densities and ρbulk and ρdry. Seven human femoral heads from hip fracture patients were computed tomography–scanned ex vivo, and 76 cylindrical trabecular bone specimens were collected. Computed tomography density was computed from computed tomography images by using a calibration Hounsfield units–based equation, whereas ρbulk, ρdry and ρash were determined experimentally. A large variation was found in the mean Hounsfield units of the bone cores (HUcore) with a constant bias from ρCT to ρash of 42.5 mg/cm3. Computed tomography and ash densities were linearly correlated ( R2 = 0.55, p < 0.001). It was demonstrated that ρash provided a good estimate of ρbulk ( R2 = 0.78, p < 0.001) and is a strong predictor of ρdry ( R2 = 0.99, p < 0.001). In addition, the ρCT was linearly related to ρbulk ( R2 = 0.43, p < 0.001) and ρdry ( R2 = 0.56, p < 0.001). In conclusion, mineral density was an appropriate predictor of ρbulk and ρdry, and ρCT was not a surrogate for ρash. There were linear relationships between ρCT and physical densities; however, following the experimental protocols of this study to determine ρCT, considerable scatter was present in the ρCT relationships.