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

Abstract

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.

A finite element analysis of tibial tritanium cones without stems in varying bone defects

“…Such time-dependent properties may accentuate loosening at the bone-implant interface when cyclic loading is applied [35], and the interfacial micromotions are also related to loading frequencies. [42]. The biomechanical performance of the cone to be used for rTKA under physiological cyclic loading needs further study by inclusion time-dependent response of bone in the computational model.…”

Distinguishing fact from fiction in finite element analysis

“…Inclusion of nonlinear geometry is warranted when large displacements are likely to arise [8] and nonlinear material properties if large strain are expected [8,9]. Time-dependent properties should be incorporated if effect of cyclic loading [10,11] or when sudden impacts are being considered. When considering implant or bone failure, wear, fatigue and fracture are all difficult outcomes to predict using the FE method due to these requirements for time dependent and non-linear material properties and nonlinear geometry.…”

“…This can be important when addressing certain clinical questions. While commonly used elastic models can provide the location at which yielding/fracture would be expected to initiate [11], more complex nonlinear models are required to predict implant loosening, fracture propagation or wear [8][9][10][11][17][18][19][20] .…”

Stress Shielding Prediction of Unicortical and Bicortical Screws: A Finite Element Analysis

“…Failure of implant fixation usually occurs due to short-term and long-term instability of the bone-implant interface. Implant material properties [1]- [2] implant geometry [3]- [4] and configuration [5]- [7] external loading [8], and interfacial bonding [9] are among the factors that affect the stability of the implant-bone interface.…”