The static friction, or "stiction-friction", in McKee-Farrar and
Charnley-Muller prostheses in a hip joint simulator was compared with
dynamic friction determined while the prostheses were oscillated. Under
physiological conditions stiction-friction differed little from dynamic
friction in both metal-on-metal and metal-on-plastic prostheses, and was
affected very little by the lubricant as long as some fluid was present.
Stiction-friction increased significantly only after relatively long
stationary periods and high loads. However, the frictional forces generated
in total hip-replacement prostheses were at least forty times higher than
those generated in normal joints and may well be enough to cause late
loosening of acetabular components by fatigue failure.