3D characterization of surface state in a knee prosthesis

From the medical point of view it is important that the surface roughness in a knee prosthesis be small in order to reduce the wear friction due to the physical contact of the prosthesis with bone. Given the complex form of the knee prosthesis, formerly the finishing process was carried out through a manual technique. However, this technique has many drawbacks. In this work a mechanochemical method (MCM) for finishing is proposed in order to obtain a proper surface state of the prosthesis. The selected MCM consisted of a mild wear procedure which employs HLB-11 as tensoactive additive. Composition of the knee prosthesis pieces was as follows: 26.5% Cr, 4.5% Mo, and the balance was cobalt. In order to optimize the prosthesis manufacturing, the evolution of the surface state along the finishing process was studied and a 3D analysis of the surface topography was carried out. To do this, two types of topometers were utilized, one of them with a tactile sensor and another one with an optical sensor. Fourier transform was applied to data roughness in order to determine the skweness (R_sk) and kurtosis (R_ku) roughness values.