Study on the Seizure Trends, Friction and Lubrication in a Total Hip Prosthesis with selfDirected Balls

Although Metal-On-Metal (MOM) Total Hip Prostheses (THP) with self directed balls have as their greatest advantage the replacement of the specific regular hip prostheses sliding movement between the femoral head and the acetabulum socket with the rolling movement between the balls, the socket and the femoral head, the lubrication side of the process is still not well known. Laboratory trials on the ball on the flat rig showed maximum values of the coefficient of friction under 0.05, and studies of lubrication with saline solution have indicated a lubrication schedule EHL, the minimum value for the thickness of the lubrication film (hmin), measured through the contact resistance methodology, being 0.06 μm, in the operation of these prostheses are obvious trends of seizure. The trials have been carried out in BSF (body simulated fluid) lubrication conditions, much closer to the real operating conditions up against the initial tests with distilled water. Seizure burdens to different loadings and contact surfaces roughness influence over the seizure burden have been determined. Even though the minimum value of the wear must be the same with the minimum value of the surfaces roughness, given the experimental conditions, it came out from the trials results on wear that the lowest level of wear is acquired at a certain value of roughness, not at the lowest level of roughness. There are obvious trends of seizure in the operation of these prostheses. However, preliminary studies on lubrication in MOM - THP also showed a clear seizure tendency. For the purposes of the present study we opted for changing the constructive version, adopting a modified motion Omnitrack solution, adapted for use in an artificial hip joint. After testing on an experimental device, the results were spectacular. The minimum friction coefficient value is 0.007, while the maximum value reaches 0.02