Surface and form metrology of polished “freeform” biological surfaces

It is a well documented fact that in the developed world the general population is aging and the percentage of elderly persons within the total population is growing rapidly. This demographic change has massively increased healthcare demands. In aging persons osteo-arthritis has been shown to be particularly problematic. Osteo-arthritis is the progressive degeneration of the natural cartilage tissue which plays a critical part in the load bearing function of hip and knee joints. Solutions to the problems caused by this tissue breakdown are administration of anti-inflammatory drugs or more normally and especially in advanced cases is the replacement of all or part of the joint with artificial joints. Worldwide, the total number of implant procedures is around 800,000. Today the life expectancy of such systems is 5–15 years. This paper outlines the development of a new technique which has been adapted to polish free form knee joint surfaces. The manufacturing route utilises a seven axes CNC Zeeko polishing machine to polish knee joint surfaces to the required form and finish. The paper discusses the process constraints and optimal settings and the surface generation process.