Modes of lubrication in human hip joints.

Cadaveric hip joints 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. Silicone fluids with viscosities from 10-2 Pa s (pascal second) to 30 Pa s were used as lubricants and the transition from mixed to full fluid film lubrication was observed around 5 x 10(-2) Pa s. Sodium carboxymethylcellulose solutions were also tested at the lower viscosities. Hyaluronidase digestion of samples of synovial fluid caused a significant increase in friction over the control samples. Trypsin digestion had no significant effect. No correlation between compliance of the cartilage and the frictional values was observed.