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

The purpose of this study was to compare computed tomography density (ρ_CT ) obtained using typical clinical computed tomography scan parameters to ash density (ρ_ash ), for the prediction of densities of femoral head trabecular bone from hip fracture patients. An experimental study was conducted to investigate the relationships between ρ_ash and ρ_CT and between each of these densities and ρ_bulk and ρ_dry . 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 ρ_bulk, ρ_dry and ρ_ash were determined experimentally. A large variation was found in the mean Hounsfield units of the bone cores (HU_core) with a constant bias from ρ_CT to ρ_ash of 42.5 mg/cm³. Computed tomography and ash densities were linearly correlated (R ² = 0.55, p < 0.001). It was demonstrated that ρ_ash provided a good estimate of ρ_bulk (R ² = 0.78, p < 0.001) and is a strong predictor of ρ_dry (R ² = 0.99, p < 0.001). In addition, the ρ_CT was linearly related to ρ_bulk (R ² = 0.43, p < 0.001) and ρ_dry (R ² = 0.56, p < 0.001). In conclusion, mineral density was an appropriate predictor of ρ_bulk and ρ_dry , and ρ_CT was not a surrogate for ρ_ash . There were linear relationships between ρ_CT and physical densities; however, following the experimental protocols of this study to determine ρ_CT , considerable scatter was present in the ρ_CT relationships.