Monitoring the bone degradation-induced loosening of osseointegrated percutaneous implant using vibration analysis

Abstract

Osseointegrated implants attach prosthetic devices directly to the skeletal system with a stable connection, allowing amputees to control prostheses with good proprioception. However, periprosthetic cortical thinning can occur if the remaining bone is stress shielded after implantation, resulting in aseptic implant loosening, and requiring revision surgery. It is therefore important to quantitatively monitor the degree of bone loss and probability of loosening to provide evidence for doctors to plan treatment. This computational study investigates the vibration behavior of a bone-implant construct by monitoring its transient response over varying degrees of bone degradation. The thickness of distal bone is progressively reduced through a revolving material removal to simulate cortical thinning due to stress shielding. First, bonded contact is adopted to represent the case of the fully osseointegrated implant under bone resorption, leading to a linear vibrational response. Next, frictional contact with 0.05 mm over-fit offset is adopted to include the non-linear contact behavior when loosening is induced by cortical thinning. The torsional mode shape of the bone-implant construct is identified through cross-spectrum analysis. The results suggest that the change in the natural frequency of the first torsional mode provides the most sensitive indicator of cortical thinning and implant loosening. The findings underpin the potential of vibration analysis in the monitoring of bone degradation-induced implant looseness.