title: A General Wear Algorithm for Wear Predictions in Total Hip Replacements
Creators: name: Toh, S
Publisher: name: Liverpool John Moores University
Year: 2023

description: Total hip replacements are known to be one of the most successful orthopaedic interventions of all time when the hip joint becomes damaged due to disease or trauma. Currently, these hip prostheses have a lifespan of approximately 15 years, however, according to the National Joint Registry (NJR) in for England, Wales, Northern Ireland, and the Isle of Man for 2021, 8% of implanted prostheses fail prematurely with wear being one of the main reasons for these failures. Wear occurs at the contacting surfaces of the hip prosthesis and is inevitable due to the surfaces being in constant contact throughout its lifespan. 

Current experimental methods to assess wear at the contacting surfaces are expensive, time-consuming and complicated. Computational wear modelling is an alternative method which is faster and cheaper compared to experimental methods and can be used to improve prosthesis design and increase overall longevity. The focus of this research is to develop a wear algorithm which can accurately predict wear at both the bearing surface and taper junction, including linear and volumetric wear damage. 

In this research, a new computational method, to predict wear at the articulating bearing surface and the taper junction surfaces of total hip prosthesis, is proposed. The method incorporates wear laws into a commercial finite element package to predict wear at the articulating bearing surface and the taper junction. The assessment of wear in this research is based on wear at the bearing surface and fretting wear at the taper junction as the primary mechanism causing surface damage. This method is unique in that it simulates both the articulating bearing surface wear and taper junction fretting wear within the same analysis with individual surface characteristics. The method is capable of modelling the fixation of the femoral head onto the femoral stem during surgery.

This method has been used to investigate different design, and clinical recommendations with results consistent with wear damage observed within current literature. This research has investigated the impact of body weight on the wear of the contacting surfaces of the THR prosthesis. The results showed that a reduction in body weight from 140kg to 100kg would decrease wear up to 30% and significantly improve the longevity of the prosthesis. The impact of adding bicycling on the wear at the contacting surfaces of the THR prosthesis was also investigated. By adding bicycling up to 80km per week, the results show that there was a significant increase in the amount of wear observed, however, the health benefits may outweigh the risks. These studies will allow for clinical recommendations post-THR to help patients return to an active lifestyle. 

The method has also investigated different design parameters, such as the different femoral head sizes on the wear on the contacting surfaces on the THR prosthesis. Four different femoral head sizes (22mm, 28mm, 32mm and 36mm) were investigated. The results showed that increasing the femoral head size would increase the volumetric wear at the bearing surface; however, the risk of dislocation decreased. This study would allow for further design modifications to further increase the lifespan of the THR prosthesis. 

The results obtained from the computational method were found to be consistent with wear damage observed within current literature and the method is able to model the wear evolution effectively. The computational method here can be used in conjunction with experimental testing to create a longer lasting hip prosthesis through design, materials and surgical approaches.