Characterisation of Corrosion and Wear in Non-Bearing Modular Orthopaedic Surfaces Using Semi-Automated Metrology

Total hip replacement (THR) is regarded as one of the most successful surgical interventions for advanced hip osteoarthritis. Modular THR designs allow intraoperative optimisation of hip biomechanics and soft tissue tension, which can translate to better post-operative outcomes. However, corrosion of the taper junction used to connect modular components continues to be an area of clinical concern.

Measuring material loss in retrievals is considered to be a requirement to understand true in-vivo implant performance. Retrieval damage of tapered components is mostly characterised using semi-quantitative visual scoring, which assigns scores between 1 and 4 depending on the extent of fretting and corrosion. This process is inherently subjective and has been widely cited as a limiting factor in the outcomes of retrieval studies. Surface metrology tools have been utilised to measure retrieved prostheses to calculate material loss: an absolute measure of damage which is rapidly replacing visual scoring. Existing research and standard test methods have largely concentrated on the femoral head taper, with relatively little literature documenting methods for measuring material loss from the stem taper counterface. The ability to measure material loss from the stem taper is of significant clinical interest, to develop explicit criteria for when to initiate revision of a well-fixed femoral stem.

The work contained within this thesis documents a root and branch methodology for determining material loss from femoral stem taper surfaces, using industry standard roundness measurement techniques. Implant deformation was also explored, in the context of surgical technique and implant design. This led to the development of an uncertainty budget, which found an expanded uncertainty of 0.807mm3 at 95% confidence. This has previously been overlooked in this specific area of research.