Experimental characterisation of coefficient of friction at bone-implant interface

Primary fixation of cementless implants is achieved through an interference fit. Successful primary fixation of press-fit components, a prerequisite for their long-term stability, is achieved through periprosthetic stress and friction at the bone-implant interface. In computational studies of interference fits, the input value of the coefficient of friction (COF) significantly influences the assessment of the primary fixation of implants. The goal of the current study was to characterise the frictional behaviour at the bone-implant interface, especially for the keel of the Oxford Unicompartmental Knee Replacement (OUKR). A test rig that enables COF measurement with one load cell was developed. Testing was conducted on a porous-coated and a smooth keel of the OUKR. COFs between these implants and plastic bone, and porcine, bovine and human cadaveric tibias were found. The mean COFs between plastic, porcine, bovine, and human bone and a smooth implant were 0.27, 0.54, 0.46 and 0.41, respectively. The mean COFs between plastic, porcine, bovine, and human bone and a porous implant were 0.99, 0.93, 0.63 and 0.99, respectively. The COFs between the porous implant surface and human bone were similar to those found in the literature.