Influence of crosslinked polyethylene structure on wear of joint replacements

Crosslinking is known to increase the wear resistance of ultra-high molecular weight polyethylene (UHMWPE) used as an acetabular cup in total hip replacement. The same wear benefit is not afforded when UHMWPE is used as a tibial component. A programmable multi-directional motion and dynamic load tribometer has been used to investigate ultra-structural development in both unirradiated (−PE) and highly crosslinked (100 kGy) UHMWPE (+PE). To investigate surface anisotropy in UHMWPE, both linear-reciprocating and elliptical wear paths were applied. Following three million elliptical cycles, crosslinking reduced wear by up to 92%. Under reciprocating motion, mean steady state wear of −PE and +PE groups was not significantly different (p=0.652). Raman spectra indicated a de-crystallisation zone on the near surface of −PE and +PE reciprocating pins. This was attributed to large strain development in conjunction with slow lamellar removal and renewal of new surface material in the lower wearing specimens. SEM images of fragmented lamellae supported this observation.