Lubricant Biochemistry Affects Polyethylene Wear in Knee Simulator Testing

Abstract Lubricant composition has been shown to influence knee simulator wear. In the present study, three types of lubricants each having different biochemistries were used in knee simulator wear tests. Alpha-calf serum was diluted with either low-ion distilled water, phosphate-buffered saline solution (PBS), or PBS with hyaluronic acid (HA), all of which affected the polyethylene wear rate. Adding HA to the PBS lubricant increased the polyethylene wear rate 2-fold. Diluting alpha-calf serum with low-ion distilled water instead of PBS increased the polyethylene wear rate 2.3-fold. Since a boundary lubrication regime was considered likely to account for these differences, the degradation to the lubricants was also monitored. Changes to the lubricant composition affected the polypeptide degradation, constituent degradation, low-molecular weight polypeptide concentration, and consequently the polyethylene wear rate. A speculative colloid-mediated boundary lubrication model was suggested, and further support was obtained by performing additional tests with osteoarthritic human synovial fluid that indicated that polypeptide constituent fractions were affected by the wear test. Diluting the alpha-calf serum lubricants with PBS, using an antibiotic-antimycotic additive to inhibit bacterial growth, and including HA created a lubricant that was similar in biochemical characteristics to human osteoarthritic synovial fluid and produced linear penetration rates and surface pitting that were comparable to those seen clinically for the same type of total knee replacements. This lubricant was recommended for producing more clinically relevant knee wear simulator testing.