Development of a method for the quantification of volumetric wear on incongruent articulating surfaces of Total Joint Replacement prostheses through the use of coordinate metrology and mathematical fitting techniques

Volumetric wear measurement of orthopaedic components is an essential tool for the evaluation of implant success. Subsequent generations of implants should generate a lower wear volume than their predecessors, as a lower wear rate can lead to a longer implant service life before failure. Wear measurements methods have been widely developed and standardised for components used in Total Hip Replacement (THR), but as is the case with most areas of research, there is a severe lag in development related to Total Knee Replacement (TKR) Prostheses, in particular in the area of standardisation. This lag is even more pronounced when considering Total Ankle Replacement (TAR) components, where very little research has been conducted due to a general lack in the number of prostheses.

This thesis presents the development of a method for the measurement of volumetric wear on UHMWPE orthopaedic components of TKR and TAR through the use of coordinate measurement machines. Currently, the only standardised method of volumetric wear measurement on TKR components is the use of Gravimetric Measurement, the assessment of small mass changes that can be divided by component density to give wear volumes. Gravimetric Measurement is widely used and considered as the “gold standard” of orthopaedic wear measurement for components worn in simulator trials. Unfortunately, gravimetric measurement is impeded by issues with fluid absorption affecting wear value calculation. However, the greatest flaw of Gravimetric Measurement is the lack of applicability to clinically relevant retrieval studies, where no pre-wear data is available.

The method developed in this study reconstructs a worn component's unworn geometry to use as reference geometry, with comparison used to calculate the volume of wear on a component. This comparison is conducted through the use of both manual and automatic wear edge definition techniques, combined with curve fitting techniques in a two-dimensional setting, followed by a three-dimensional calculation of volumetric wear on the surface.

Numerous studies have been conducted to evaluate the efficacy of the CMM measurement method developed and to refine aspects of the post-measurement data analysis method. These studies have considered both wear-simulated and retrieved TKR components, as well as an artificially created TKR component. Volumetric wear analysis has also been performed on wear-simulated TAR components.

These studies found that the method developed provided accurate and repeatable results for volumetric wear on all cohorts of components across a wide range in terms of the severity of wear, with the effectiveness and accuracy of the method developed analysed.