Surface geometry of retrieved McKee-Farrar total hip replacements

A coordinate measurement machine was used to determine the surface geometry of 22 retrieved McKee-Farrar total hip replacements. The radial clearance of each acetabular cup-femoral head pair was computed to see whether there was potential for hydrodynamic lubrication. The surface geometry was used to estimate the volumetric wear for the acetabular cup and the femoral head, and to assess whether those prostheses that had the potential for fluid film lubrication also displayed lower wear. The volumetric wear rate for each prosthesis was estimated by dividing the volumetric wear by the corresponding service life. Two distinct wear patterns were seen on the femoral head. Prostheses displaying polar wear on the femoral head showed significantly greater service lives than those displaying non-polar wear. Although several prostheses had clearances that provided for the possibility of hydrodynamic lubrication, no correlation could be found between clearance and the measured wear.