The lubrication of natural and artificial hip joints

Cadaveric hip joints and prostheses were tested in a hip Function simulator which subjected the Femoral head to a cycle of loading and oscillation similar to that experienced during walking, and measured the Frictional torque transmitted to the acetabulum. For natural joints, silicone Fluids with viscosities From 10(^-2) Pa s to 30 Pa s were used as lubricants and Full Fluid Film lubrication was observed above 10(^-1) Pa s. Sodium carboxymethylcellulose solutions were also tested at the lower viscosities. Hyaluronic acid was added to one sample of synovial Fluid to increase its viscosity range and other synovial Fluid samples were digested enzymatically. Hyaluronidase digestion caused a significant increase in Friction Factor over the control samples whereas tryptic digestion had no consistent effect. No correlation between compliance of the cartilage and Frictional values was observed. Experimental prostheses with a compliant lining in the acetabular component were manufactured From a silicone elastomer. The layers varied From 0.5 to 3 mm thick, and two different clearances were tested. The prostheses were tested with SCMC and silicone Fluids. The Friction Factors obtained at low loads were higher than For a Charnley prosthesis. The swelling effect of the silicone Fluids on the elastomeric linings was investigated along with the effective elastic modulus of the arrangements.