How Angular Mismatch and Surface Topography in Modular Head-Stem Taper Junctions in Total Hip Replacements Affects...

Morse-type tapers at the head-stem junction in total hip replacements (THRs) provide many benefits to permit a successful surgical outcome. However, with the introduction of modular tapered devices comes complications associated with fluid ingress and motion at the interface that can cause fretting corrosion, which has been implicated in clinical failure. Increased surface roughness amplitude (R_a) and angular mismatch to ensure taper contact closer to the equator of the femoral head are design features introduced for use with ceramic heads but have been adopted by metal head couples. While increased surface roughness amplitude has been found to contribute to fretting corrosion, there is a distinct lack of systematic studies investigating the interactions between angular mismatch and R_a. This study measured the fretting corrosion and motion response of clinically representative samples, in part reference to ASTM F1875, when subjected to uniaxial incremental dynamic loading. The fretting corrosion response was measured in situ with an integrated three electrode electrochemical cell. Motion at the head-neck interface was measured with a bespoke motion measurement solution based on eddy-current principles which uses four sensors to allow motion to be fully characterised in three dimensions. Key findings from this study included a 5-10-fold increase in current measured in the increased roughness amplitude samples, suggesting an increased susceptibility to fretting corrosion without a corresponding increase in motion. The distal samples engaged around the opening of the taper interface and presented the lowest current measurements but most off-axis subsidence. Findings from this study indicate that optimisation of the taper interfaces in THR, in terms of fretting corrosion and motion, can be made and can be assessed using short-term preclinical tests.