Predicting friction at the bone – Implant interface in cementless total knee arthroplasty

Cementless total knee arthroplasty (TKA) components have rough and porous surface coatings which can enhance bone ingrowth and stability at the bone-implant. To achieve primary stability in the postoperative period where no apposition is formed, the resistance against motions between bone and implant is optimized by increasing the friction at the interface. This is necessary, as excessive relative motions can inhibit bone ingrowth, which might result in loosening and pain. In this research, it was found that the friction can be predicted by measuring the surface morphology of rough implants, and calculating the corresponding perpendicular and lateral contact area parameters. The ratio between these areas, is used to predict the resulting coefficient of friction (COF). This is validated experimentally, by analysing the tribological behaviour of 2 porous and rough titanium coatings against human cadaveric knee bones using reciprocal friction tests with varying normal loads. The results for 2 different coatings showed similar findings for the predicted COF (0.75 and 0.88) versus the calculated values based on the measurement (0.82 and 0.86) proving the feasibility of the approach.