A computational approach to fretting wear prediction at the head–stem taper junction of total hip replacements

Abstract

Wear is one of the main reasons for failure of modular total hip replacements. Recent evidence suggests that fretting wear occurs at the taper junction which provides fixation between the prosthesis femoral head and stem components. The fine metallic wear debris that is released can lead to adverse soft-tissue reactions which can necessitate a revision surgery. The present study proposes a computational methodology utilising an energy wear law and a 3D finite element model to predict fretting wear at the taper junction. The method is novel in that it simulates the weakening of the initial taper 'fixation' (created at impaction of the head onto the stem in surgery) due to the wearing process. The taper fixation is modelled using a contact analysis with overlapped meshes at the taper junction. The reduction in fixation is modelled by progressive removal of the overlap between components based on calculated wear. The fretting wear analysis approach has been shown to model the evolution of wear effectively; however, it has been shown that accurate, quantitative values for wear are critically dependant on mesh refinement, wear scaling factor and fraction, wear coefficient used and knowledge of the device loading history. The method has been implemented with a 3D finite element model of the taper junction of a commercial total hip replacement. This has been used to determine taper wear patterns, wear damage and wear rates which have been shown to be consistant with those found from observation and measurement of retrieved prostheses. The numerical method could be used to consider the effect of design changes and clinical technique on subsequent fretting wear in modular prosthetic devices.

A large taper mismatch is one of the key factors behind high wear rates and failure at the taper junction of total hip replacements: A finite element wear analysis

“…A study on the effect of β on the calculation of wear undertaken in the previous study has demonstrated that β =10 5 provides converged results (English et al, 2015). However, in this study, by employing a new model with a more realistic boundary condition and a refined mesh at the contact area, the β value has been converged at 250,000 load cycles, which further reduced the computational wear analysis time.…”

“…This law considers the interfacial shear work and relative motion as predominant parameters to calculate the volumetric wear. Its implementation in finite element analysis has been explained previously (English et al, 2015). Briefly, according to the "Dissipated Energy" wear law, the cyclic wear depth (W c ) for a single cycle of loading can be presented using Equation 1,…”

“…As explained in (English et al, 2015), the Dissipated Energy wear law was applied to a wear algorithm as a custom user plug-in linked with ABAQUS (6.14-3 ABAQUS Inc) software. For this study, the algorithm has been further developed, generalised and optimised in order to reduce the computational cost.…”

“…The elements at the contact interface were matched and refined with a total of 9600 paired elements at the contact interface. This was followed by a mesh convergence study (the procedure was previously explained in (English et al, 2015)), which…”

“…As such, in this study an initial impaction force of 4 kN was considered for all the models (shown in Figure 2a and c). This impaction analysis, known as "phase 1" of the wear methodology (see (English et al, 2015)) was executed as a dynamic implicit analysis at commencement of the wear analysis.…”