Influence of kinematics on the wear of a total ankle replacement

Alexandra Smyth,John Fisher,Silvia Suñer,Claire Brockett

doi:10.1016/j.jbiomech.2017.01.001

Alexandra Smyth, John Fisher + Show 2 more

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https://doi.org/10.1016/j.jbiomech.2017.01.001

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Abstract

Total ankle replacement (TAR) is an alternative to fusion, replacing the degenerated joint with a mechanical motion-preserving alternative. Minimal pre-clinical testing has been reported to date and existing wear testing standards lack definition. Ankle gait is complex, therefore the aim of this study was to investigate the effect on wear of a range of different ankle gait kinematic inputs. Five Zenith (Corin Group) TARs were tested in a modified knee simulator for twelve million cycles (Mc). Different combinations of IR rotation and AP displacement were applied every 2Mc to understand the effects of the individual kinematics. Wear was assessed gravimetrically every Mc and surface profilometry undertaken after each condition. With the initial unidirectional input with no AP displacement the wear rate measured 1.2±0.6mm3/Mc. The addition of 11° rotation and 9mm of AP displacement caused a statistically significant increase in the wear rate to 25.8±3.1mm3/Mc. These inputs seen a significant decrease in the surface roughness at the tibial articulation. Following polishing three displacement values were tested; 0, 4 and 9mm with no significant difference in wear rate ranging 11.8–15.2mm3/Mc. TAR wear rates were shown to be highly dependent on the addition of internal/external rotation within the gait profile with multidirectional kinematics proving vital in the accurate wear testing of TARs. Prior to surface polishing wear rates were significantly higher but once in a steady state the AP displacement had no significant effect on the wear.

Highlights

Total ankle replacement (TAR) is an alternative to fusion, replacing the degenerated joint with a mechanical motion-preserving alternative
Far displacement controlled wear testing on TARs has been limited mostly to a set of conditions defined by Bell and Fisher (2007) and in 2014, an ASTM standard was updated to highlight the need for wear testing on new bearing materials but without specific conditions (ASTM, 2014)
The wear of a TAR was assessed through several kinematic conditions

Summary

Introduction

Total ankle replacement (TAR) is an alternative to fusion, replacing the degenerated joint with a mechanical motion-preserving alternative. Far displacement controlled wear testing on TARs has been limited mostly to a set of conditions defined by Bell and Fisher (2007) and in 2014, an ASTM standard was updated to highlight the need for wear testing on new bearing materials but without specific conditions (ASTM, 2014). The wear rates measured without anterior/posterior (AP) displacement 10.36711.8 mm3/Mc for the BP and 3.38710.0 mm3/Mc for the Mobility These wear rates increased to 16.4717.4 mm3/Mc and 10.4714.7 mm3/Mc, respectively, with the addition of displacement for a final Mcs. At the same time Affatato et al (2007) applied similar gait conditions to the BOX Ankle (Finsbury Orthopaedics Ltd., Leatherhead, UK), with lower forces and higher AP simulated in deionised water to substantiate the use of a knee simulator for ankle wear simulation. Clinical failure of TAR and limited studies into wear testing defined a need for further exploration into TAR wear to understand the effects of the kinematics on the mobile bearing design. Following trends which were discovered investigating total knee replacement wear, it was hypothesised that the magnitude of rotation and displacement occurring at the ankle would have a significant effect on the wear of a mobile bearing total ankle replacement

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