Effect of loading frequency on deformations at the bone-implant interface

This study considers the time-dependent behaviour of bone in the context of loosening of metal implants, which is one of the typical complications of joint replacement and fracture-fixation surgeries. We employed viscoelastic properties developed from our previous experimental studies for trabecular bone in a representative bone-implant construct, which was subjected to cyclic loading at varying loading frequencies. We found that the separation between the bone and the implant is a function of loading frequency and increases with number of loading cycles applied. Our analysis shows that at the start of cyclic loading, a higher frequency results in a lower displacement response of bone at the bone-implant interface; however, after the bone-implant system has been subjected to a large number of cycles (>500 cycles in this study), higher interfacial displacements are observed at higher loading frequencies. In other words, higher loading frequencies will not result in bone-implant separation if limited number of cycles are applied. In all cases, interfacial displacements increase as bone volume ratio decreases. This simple approach can be used to evaluate the mechanical environment in bone-implant systems due to cyclic loading which commonly used time-independent models that are unable to simulate. The approach can also be used to evaluate implant loosening due to cyclic loading.