Accurate diagnosis of bone degradation-induced prosthesis loosening using harmonic vibration analysis: An experimental study with a simplified model

Abstract. The Osseointegration Prosthetic Limb is a transfemoral implant that attaches the prosthesis directly to the bone, providing greater comfort than a traditional socket. However, transferring load to an implant can induce stress shielding and bone resorption, potentially leading to loosening and pain. This experimental study investigates the nonlinear vibration response of a simplified femur-implant model as the basis for a non-invasive strategy to monitor implant loosening. Three femur-implant assemblies were constructed with prescribed levels of interference fit between the bone and implant. To mimic bone degradation due to stress shielding, bone thickness was reduced by material removal, which led to a reduction of contact stability. In the vibration analysis, a static longitudinal gait force was applied at the distal end of the implant to preload it with a load representative of the compression experienced during walking. Subsequently, the model was excited at the resonant frequency of the first torsional vibration mode to assess interfacial contact. Slippage at the interface occurs when the interfacial shear stress exceeds a prescribed critical threshold, leading to the generation of higher-order harmonics in the vibration response. The evolution of these harmonics was analysed in relation to the magnitude of torsional excitation and contact stability. Results suggest that the presence of the higher-order harmonic serves as a reliable indicator of interfacial slippage, and the corresponding load level provides a quantitative index of the implant's load-bearing capacity. These findings demonstrate the feasibility of using nonlinear vibration analysis, as a non-invasive means of assessing the criticality of the bone-implant interface.