A Study of the Role of Synovial Fluid and its Constituents in the Friction and Lubrication of Human Hip Joints

Abstract

Human hip joints have been studied in a pendulum apparatus and a joint simulator to determine the lubrication mechanisms active in normal physiological activities. Various lubricants have been used to lubricate the hip joints including bovine and human synovial fluid, synovial fluid which has been digested with hyaluronidase or trypsin, silicone fluids of different viscosities, as well as synovial fluid and Ringer's solution which have had their viscosities increased by the addition of hyaluronic acid. The results indicate that under continuous dynamic loading, fluid film lubrication seems to prevail while under static loading, mixed lubrication exists. Increasing the viscosity of the lubricant from very low values (i.e. from 10-3 Pa.s) leads to a reduction in friction, indicating mixed lubrication, until a value of about 0.050 Pa.s was achieved. Further increases seemed to indicate that fluid film lubrication was then present.