A Method to Improve Experimental Validation of Finite-Element Models of Long Bones

Abstract:  Finite-element (FE) simulations are extremely sensitive to boundary conditions, including the position of applied forces. This is particularly critical for FE models of bones, where the lack of a univocal reference system makes identifying the boundary conditions difficult. The aims of this work were to design a transducer (FP-transducer) to accurately determine the position of the resultant joint force during in vitro tests, and to assess its accuracy for future application in validating numerical models of long bones. A strain gauge-based transducer was designed to indirectly measure the position of the force applied to the long bones during in vitro tests, by measuring the reaction moments about two perpendicular axes, generated by the force applied. Validation tests were performed to quantify the intrinsic precision of the FP-transducer (by applying calibrated forces at known locations), and the overall accuracy when the FP-transducer was included in a typical set-up for long bone testing. The intrinsic accuracy of the FP-transducer when used to calculate the position of an offset force was satisfactory (0.66 mm). The overall accuracy of the FP-transducer in measuring the position of the applied force, when included in a typical set-up for long bone testing was 0.85 mm. In vitro validation of FE models of long bones may, therefore, be improved, thanks to a more accurate determination of the force application point.