Femoral neck impingement occurs clinically in total hip replacements (THR) when the acetabular liner articulates against the neck of a femoral stem prosthesis. This may occur Neck impingement testing per ASTM F2582-14 was carried out on four groups of artificially aged acetabular liners (per ASTM F2003-15) made from GUR 1020 UHMWPE which was re-melted and cross-linked at 7.5 Mrad. Group A (n=3) and B (n=3) consisted of 28mm diameter femoral heads articulating on 28mm ID × 44mm OD acetabular liners. Group C (n=3) and D (n=3) consisted of 40mm diameter femoral heads articulating on lipped 40mm ID × 56mm OD 10° face changing acetabular liners. All acetabular liners were tested in production equivalent shell-fixtures mounted at 0° initial inclination angle. Femoral stems were potted in resin to fit respective simulator test fixtures. Testing was conducted in bovine serum diluted to 18mg/mL protein content supplemented with sodium azide and EDTA. Groups A and C were tested on a Prosim; Groups B and D were tested on an AMTI. Physical examination and coordination measurement machine (CMM) analyses were conducted on all liners pre-test and at 0.2 million cycle intervals to monitor possible failure mechanisms. Testing was conducted for 1.0 million cycles or until failure. An Abaqus/Explicit model was created to investigate relative motions and contact areas resulting from initial impingement kinematics for each test group.Introduction
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Titanium and its alloys are attractive biomaterials attributable to their desirable corrosion, mechanical, biocompatibility and osseointegration properties. In particular, β – titanium alloys like the TMZF possess other advantages such as its lower modulus compared to Ti6Al4V alloy. This reduces stress shielding effect in Total Hip Arthroplasty (THA) and the replacement of V in the Ti6Al4V alloy, eliminates A ball-on-flat configuration was utilised in this study to achieve a Hertzian point contact for CoCrMo – Ti6Al4V and CoCrMo – TMZF material combinations. These were assessed at a fretting displacement of ±50 µm at an initial contact pressure of 1 GPa. Each fretting test lasted 6000 cycles at a frequency of 1 Hz. A two-electrode cell set-up was used to monitor Introduction
Method
Titanium and its alloys are attractive biomaterials attributable to their desirable corrosion, mechanical, biocompatibility and osseointegration properties. Ti6Al4V alloy in particular remains a prominent biomaterial used in Total Hip Arthroplasty (THA) today. This is partly due to biocompatibility and stress shielding issues with CoCrMo alloys, resulting in its increasing side-lining from the THA construct. For several decades now, research efforts have been dedicated to understanding wear, corrosion and surface degradation processes in implant materials. Only recently have researchers shown interest in understanding the subsurface implications of fretting and the role it plays on implant fracture. The purpose of this study was to utilise advanced microscopy and spectroscopy techniques to characterise fretting-induced subsurface transformations in Ti6Al4V. This makes mapping specific regions that are most prone to wear and fatigue failures at the modular taper interface of THA probable. Thus, informing a proactive approach to component design and material selection. A ball-on-flat configuration was utilised in this study to achieve a Hertzian point contact for a CoCrMo – Ti6Al4V material combination. Four fretting displacement amplitudes were assessed: ±10, ±25, ±50 and ±150 µm. An initial contact pressure of 1 GPa was used for all fretting tests in this study and each fretting test lasted 6000 cycles at a frequency of 1 Hz. The simulated physiological solution consisted of Foetal Bovine Serum (FBS) diluted to 25% with Phosphate Buffered Saline (PBS) and 0.03% Sodium Azide (SA) balance. The temperature was kept at ∼37°C. Subsurface transformations in the Ti6Al4V alloy was characterised using the Transmission Electron Microscopy (TEM) to obtain high resolution micrographs. The samples were prepared using a FIB-SEM. Bright-field, dark-field and selected area electron diffraction (SAED) patterns were all captured using a scanning TEM (STEM) and Energy Dispersed X-Ray spectroscopy (EDX) mapping was carried out.Introduction
Method
Fretting corrosion at the Head-Neck taper interface of Large Metal on Metal (MoM), Metal on Polymer (MoP) and Ceramic on Ceramic (CoC) total hip arthroplasty (THA) remains a clinical concern. Ceramic femoral heads have gained a lot of attention more recently as a possible way to mitigate/reduce the dissolution of Cobalt Chromium ions. The objective of this study is to assess the fretting corrosion currents emanating from four material combinations for which Ti6Al4V and Co28Cr6Mo are the neck components of Co28Cr6Mo and BIOLOX®delta femoral heads at three different cyclic loads. 12/14 Ti6Al4V and Co28Cr6Mo spigots (designed to geometrically represent the stem) were impacted against Ø36mm Co28Cr6Mo and BIOLOX®delta femoral heads with a static force of 2kN as shown in Figure 1. The tapers were immersed in 25% v/v diluted Foetal Bovine Serum, PBS balance and 0.03% Sodium Azide at room temperature. In-situ electrochemistry was facilitated using a 3-eletrode cell arrangement whereby the neck components were the working electrode, Ag/AgCl was the reference electrode and a platinum counter electrode completed the cell. All combinations were held at a potential of 0V vs. Ag/AgCl and the cyclic load applied unto each couple were 1kN, 3kN and 5kN at 1Hz consecutively (see Figure 2). The fretting corrosion currents were converted into cumulative charge transferred (Q) by integrating the wear enhanced corrosion current.Introduction
Method
Cobalt-Chromium-Molybdenum (CoCr) and Titanium-Aluminium-Vanadium (Ti) alloys are the most commonly used alloys used for Total Hip Replacement due to their excellent biocompatibility and mechanical properties. However, both are susceptible to fretting corrosion In-vivo. The objective of this study was to understand the damage mechanism of both combinations through a sub-surface damage assessment of the alloys at various fretting amplitudes using the Transmission Electron Microscopy (TEM – CM200 FEGTEM). The TEM was used to attain a cross sectional view of the alloys in orderto see the effect of high shear stress on the grain structure. The two combinations were fretted at a maximum contact pressure of 1 GPa in a Ball – on – Plate configuration for displacement amplitudes of 10μm, 25μm, 50μm and 150μm. The contact was lubricated with 25% v/v Foetal Bovine Serum (FBS), diluted with Phosphate Buffered Saline (PBS). The material loss through wear and corrosion from the fretting contact were quantified using the Visual Scanning Interferometry (VSI). The TEM samples were obtained using the Focused Ion Beam (FIB – FEA Nova 200 Nanolab). Samples were obtained from regions of high stress (shaded in red) [Fig. 1] for both CoCr and Ti flat of the CoCr–CoCr and CoCr–Ti couples respectively.Introduction
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