Rheological Modelling of Knee Joints

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Degenerative action, whether due to natural aging, disease or injury, is a common occurrence during the lifetime of a human joint. 200,000 corrective procedures are performed yearly in the US and 80,000 in the UK, with an expected growth of 170% by 2020.However, implants are not without complications; there are numerous areas of incompetency in current designs. For instance, the current service life of an implant is about 15 years, which is inconvenient for patients planning to live beyond that. Furthermore, the wear from metal implants causes metal ion release which is best avoided in a biological context, as well as causing loosening and failure. While there are numerous experimental studies into wear of implants, numerical modelling is a relatively less explored albeit equally important aspect to implant design. Both are necessary for the validation of an implant design. A numerical model would allow resource efficient optimisation of the design of an implant suited for different usage requirements.Human joints closely resemble elastohydrodynamic lubrication, with synovial fluid as the lubricant. While most previous studies consider it to be a Newtonian fluid within the regimes of everyday usage, there is experimental evidence to suggest otherwise.This provides an incentive to investigate this matter. If a rheological model for synovial fluid can be developed, through regression analysis or otherwise, it can be implemented into already existing models of human joints. This is of significance to the current knee modelling effort being carried out by the department, as it can be potentially incorporated into those models as well as being examined for suitability for other joints.