Improved friction and wear performance in polymeric components of orthopaedic bearings.

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Nearly 25,000 Canadians and 600,000 worldwide are implanted with an artificial knee each year. These devices are most often designed using specialized components made of metal (cobalt chrome) and plastic (ultrahigh molecular weight polyethylene). They are the treatment of choice for severe degenerative joint disease, and they are now being implanted in active patients, some as young as 45. As a result, there is an increased need to improve their durability, particularly with respect to wear in the plastic component. While there have been improvements in the design of polyethylene for use in hips, this has not been the case for highly stressed joints such as the knee. This project examines a novel way of treating the plastic material surface to reduce wear. It is thought that small indentations, or dimples, in the polyethylene surface will entrain joint fluid that will help lubricate the joint and also reduce the stress on the plastic itself. With reduced stress, reduced plastic wear should result. It is reasoned that human cartilage morphology, which has naturally occurring dimples less than 40 micrometers in diameter and 15 micrometers deep, could be used as a model for the surface texture. This geometry will be reproduced on polyethylene surfaces using specialized processing facilities at Queen's and tested to determine if this can reduce friction and wear in laboratory specimens. If successful, the texturing process will be evaluated on artificial joints in a wear simulator that reproduces loads and motion that occur in real life. The aim is to reduce the need to replace worn out artificial knees by improving their durability beyond the 15 years currently expected and provide a growing number of aging adults with a lifetime of activity well past what is now possible.