A Simulator Study of Friction in Total Replacement Hip Joints

Abstract

Frictional behaviour of 22 different femoral head-acetabular cup combinations was studied on a new servo-hydraulic microcomputer-controlled hip joint simulator using various flexion-extension angle and superior-inferior load set value waveforms and using distilled water at 37 ± 1°C as lubricant. Six different head materials were included in the study, whereas all cups were ultra-high molecular weight polyethylene (UHMWPE). Most head-cup combinations studied are commercially available. No distinctly superior joint design can he pointed out, but the frictional behaviour of alumina ceramic against UHMWPE proved overall most favourable ( μmin was 0.02), whereas that of non-ion-implanted titanium alloy Ti-6Al-4V against UHMWPE proved strikingly poor ( μmax was 0.15). The lowest frictional torque was in 22 mm joints, but frictional torque did not always increase straightforwardly with increasing diameter of the femoral head. The measurements form an extensive comparison between a wide variety of head-cup combinations. The simulator is apparently a useful instrument in the study of frictional behaviour of new designs, materials, surface treatments and coatings that are frequently introduced.