Calibration of the in-vivo-measurement device on aluminum model and intact tibiae. Calibration curve of the measurement device obtained from values measured on aluminum bars with interconnected modules of varying stiffness (solid line). The change in measurement (apparent stiffness, y-axis) on the effect of pin osteolysis was determined (◊: All the pins are firmly fixed, ▽: one pin loose, □: four pins loose). For bending stiffness up to 10 Nm/degree, the measurement error remains acceptably small, even under the worst condition of all pins loose. Validation of the calibration model was tested on intact tibiae (green ○). The calculated bending stiffness tends to be smaller than the actual bending stiffness (mean value 5.4%, SD ± 6.2).