Friction and wear of the Durham finger prosthesis

Abstract

Rheumatoid arthritis of the hand can cause deformities that may severally impair hand function. Surgical procedures including total joint replacement have been developed over the last thirty years to treat patients with metacarpophalangeal deformity. The Centre of Biomedical Engineering at Durham University contributed to this field of research by designing a new artificial metacarpophalangeal (MCP) joint intended to operate in the same manner as the natural joint. The Durham MCP prosthesis is a non constrained two piece all XLPE device which allows flexion-extension, adduction-abduction and little rotation movements, hi order to test the wear behaviour of the Durham MCP prosthesis before implanting it, a new finger wear simulator was also designed at Durham University and the prosthesis gave acceptable results from a wear point of view, hi 1997 clinical trials started and to date five people have been implanted with the Durham MCP prosthesis. In order to investigate the in vitro wear behaviour of the Durham MCP prosthesis further, nine wear tests were undertaken during this research using the finger wear simulator. For the first time EtO-sterilized XLPE prostheses were tested and their performances in bovine serum were very promising. This might indicate that ethylene oxide gas is a valid alternative to gamma irradiation for sterilizing the Durham MCP prosthesis as it doesn't seem to influence its wear properties. Wear debris was also analyzed showing that the majority of the particles detected were less than lμm in size. In order to investigate the frictional properties of the Durham MCP prosthesis, a new finger friction simulator has been designed, manufactured and validated during this research. Various tests were undertaken using different pairs of materials in order to compare the results with literature and validate the simulator. The new finger friction simulator appears to give consistent results and might then be used to record the variations of the coefficient of friction in the all XLPE Durham MCP prosthesis during the wear tests.