A Review of Lubrication Conditions for Wear Simulation in Artificial Hip Replacements

It is essential to evaluate the wear behavior of joint replacement materials and designs. While synovial fluid is the biological joint lubricant, it is present in too small quantities to use for wear simulations. A variety of lubricants have been used, such as water, saline solutions, synovial fluid components (hyaluronic acid, lubricin, and phospholipids), serum, and custom-made lubricants. We review studies from our Loma Linda University Medical Center lab and other labs using metal-on-polyethylene, exploring the benefits and deficiencies of these pseudo-synovial fluids. Serum is used extensively as the lubricant because its results most closely match clinical results with polyethylene bearings. We summarize laboratory experiments that have explored the effects of serum with differences in proteins (concentration, type, and ratio), volume, viscosity, temperature, and additives and their wear response. Protein precipitates seem to protect the implants from wear. The properties of current lubricants, in particular the roles of proteins, are the current focus in the search for an ideal joint analogue fluid.