Abstract
A more robust pre-clinical wear simulation framework is required in order to simulate wider and higher ranges of activities, observed in different patient populations such as younger more active patients. Such a framework will help to understand and address the reported higher failure rates for younger and more active patients (National_Joint_Registry, 2016). The current study has developed and validated a comprehensive combined experimental and computational framework for pre-clinical wear simulation of total knee replacements (TKR).The input mechanical (elastic modulus and Poisson’s ratio) and wear parameters of the moderately cross-linked ultra-high molecular weight polyethylene (UHMWPE) bearing material were independently measured from experimental studies under realistic test conditions, similar to the loading conditions found in the total knee replacements. The wear predictions from the computational wear simulation were validated against the direct experimental wear measurements for size 3 Sigma curved total knee replacements (DePuy, UK) in an independent experimental wear simulation study under three different daily activities; walking, deep squat, and stairs ascending kinematic conditions.The measured compressive mechanical properties of the moderately cross-linked UHMWPE material were more than 20% lower than that reported in the literature under tensile test conditions. The pin-on-plate wear coefficient of moderately cross-linked UHMWPE was significantly dependant of the contact stress and the degree of cross-shear at the articulating surfaces.The computational wear predictions for the TKR from the current framework were consistent and in a good agreement with the independent full TKR experimental wear simulation measurements, with 0.94 coefficient of determination of the framework. In addition, the comprehensive combined experimental and computational framework was able to explain the complex experimental wear trends from the three different daily activities investigated. Therefore, such a framework can be adopted as a pre-clinical simulation approach to optimise different designs, materials, as well as patient’s specific total knee replacements for a range of activities.
Highlights
The number of younger and more active patients requiring total knee replacements (TKR) is increasing (National_Joint_Registry, 2016)
Pre-clinical pin-on-plate and pin-ondisk studies are usually run under simplified test conditions and geometry configurations they provide significant insights into wear characteristics and wear mechanisms of the articulating as well as fixation interfaces of the bearing materials (Zhang et al, 2015; Brockett et al, 2016a)
Clinical and experimental wear studies have shown that wear is dependant on the cross-shear ratio (CS) and the contact stress (P) at the articulating surfaces (Wang, 2001; Foran et al, 2004; Kang et al, 2008b; Abdelgaied et al, 2013b; O’brien et al, 2015)
Summary
The number of younger and more active patients requiring total knee replacements (TKR) is increasing (National_Joint_Registry, 2016). Pre-clinical pin-on-plate and pin-on-disk testers have been extensively used to screen the performance and explore the influence of parameters such as lubricant, sliding distance, contact stress, and crossshear ratio on the wear of orthopaedic bearing materials (Barbour et al, 1995; Saikko, 2006, 2014; Abdelgaied et al, 2013b; Zhang et al, 2015; Brockett et al, 2016a). Pre-clinical pin-on-plate and pin-ondisk studies are usually run under simplified test conditions and geometry configurations they provide significant insights into wear characteristics and wear mechanisms of the articulating as well as fixation interfaces of the bearing materials (Zhang et al, 2015; Brockett et al, 2016a). Pre-clinical pin-on-plate and pin-on-disk studies provide the input parameters and validation required for reliable and accurate pre-clinical computational simulation studies (Fregly et al, 2005; Willing and Kim, 2009b; Abdelgaied et al, 2011, 2013a)
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