Impact of a phantomless calibration method on two finite element models predicting metastasised femoral strength

<title>Abstract</title> <p>Computed tomography (CT) based finite element (FE) models for bone strength prediction of metastasised femurs require calibration of Hounsfield Units (HU) to bone mineral density, to then derive mechanical parameters. This study aimed to evaluate a phantomless calibration method for two FE models of femoral strength prediction (Lyon and Leuven models), which notably differ in their constitutive law (linear for Lyon model, non-linear for Leuven model). Femurs of 54 patients with bone metastases were CT-scanned with a calibration phantom. Lyon and Leuven models were created for each femur, following calibration using (i) the phantom, and (ii) the air-fat-muscle (AFM) calibration method, where HU peaks of air, fat, and muscle are linearly fitted to reference density values. A very good reproducibility of the AFM method was found for both models, and a significant correlation with the phantom-based calibration in terms of apparent density (R² = 0.78, p&lt;0.01) and femoral strength (R² = 0.85, p&lt;0.01). Limits of agreement between each method were narrower for Lyon model than for Leuven model, suggesting that a linear model is less sensitive to density calibration. The phantomless calibration method is a promising approach to broaden routine use of bone strength numerical simulation in bone metastatic patients.</p>