NEW STUDY ON FRICTION IN A MOM TOTAL HIP PROSTHESIS WITH BALLS IN SELF-DIRECTED MOTION

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. Tests with balls on a flat rig showed maximum values for the friction coefficient of under 0.05 while studies of lubrication with saline solution have indicated an EHL lubrication schedule, with a minimum value for the thickness of the lubrication film (hmin), measured through the contact resistance methodology, of 0.06 μm. There are obvious trends of seizure in the operation of these prostheses. However, preliminary studies on lubrication in Metal-On-Metal prostheses 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